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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 2, Number 3 (HABITAT, 1993, 42 p.)
View the document(introduction...)
View the documentForeword
View the documentSustainable development and the construction industry
View the documentKenya: Fibre-concrete roofing technology: Adaptation and progress*
View the documentZimbabwe: Low-income housing pilot projects
View the documentIndia: Technology profile: Solar timber seasoning kiln*
View the documentPublications review
View the documentEvents
View the documentForthcoming events


August 1993
ISSN 1012-9812

United Nations Centre for Human Settlements (Habitat)
Nairobi, 1993



The Network of African Countries on Local Building Materials and Technologies has the objective of strengthening local technological capacity through facilitating information flow, regional co-operation and transfer of appropriate technologies in low-cost and innovative building materials sector in African countries.

The Journal of the Network, currently published biannually, aims to provide a channel for information that is available and could be of use by professionals, technicians, researchers, scientists as well as policy and decision makers. It is a medium for information exchange and facilitator for acquisition of suitable technologies and know-how by needy countries.

Efforts are made to compile, process and publish articles and technical papers originated, mainly, in African region, however, as deemed appropriate and subject to availability, research findings and technological information from countries outside the African region are also included to stimulate interregional cooperation as well.


This Journal welcomes information or articles on low-cost innovations in building-materials technology. Information in the form of technical and policy papers, illustrations, news items and announcements of events can be sent from individuals or institutions in the private or public sector, from within and outside the African region. All correspondence on the Journal should be addressed to the Chief, Building and Infrastructure Technology Section, Research and Development Division, UNCHS (Habitat), P.O. Box 30030, Nairobi Kenya.

The views expressed in this Journal do not necessarily reflect those of the United Nations. Mention of firm names and commercial products do not imply the endorsement of UNCHS (Habitat). The reprinting of any of the material in this publication is welcome, provided that the source is mentioned and one copy sent to UNCHS (Habitat).

National Network Institutions

Cyprus Organization of Standards and Control Quality
Ministry of Commerce and Industry

Department of Civil Engineering
University of Addis Ababa

Building and Road Research Institute (BRRI)
Kumasi University

Housing and Building Research Institute (HABRI)
College of Architecture and Engineering
University of Nairobi

Department of civil Engineering
The Polytechnic
University of Malawi

Department of Architecture and Civil Engineering
University of Malta

School of Industrial Technology
University of Mauritius

Nigerian Building and Road Research
Institute (NBRRI)

Faculty of Engineering
Fourah Bay College
University of Sierra Leone
Sierra Leone

Geological Survey Mines Department
Ministry of Lands and Mines

Building Research Unit (BRU)
United Republic of Tanzania

Ministry of Public Construction and National Housing


Construction-industry activities are directly linked with overall socio-economic development in every country. The industry provides the means to meet basic human needs, including shelter and infrastructure, and contributes to the realization of economic goals and better living conditions. However, the continuing dependence of the industry on non-renewable natural resources and the impact of its operations on the physical environment and the ecosystem are major constraints to its growth.

Sustainable construction-industry activities require a policy framework that effectively addresses the twin requirements of the sustainable management of natural resources and the control of degradation of the environment associated with such activities. There is a growing perception, worldwide, that construction activities must progressively harmonize with environmental needs to sustain their growth in the term. To achieve this, it is necessary to bridge the current gap of objective information on the environmental implications of construction products and processes. Wide dissemination of such information among practitioners in the industry and the public is equally crucial. Simultaneously, there is an urgent need to develop capacity in developing countries for resource management and pollution control in construction. Concerted efforts in this regard will lead to the formulation of environmental policies related to construction, development of standards, enforcement through legislation, and finally to improved construction practices.

UNCHS (Habitat) has focused on the inter-relationship between construction and environment in recent years. The recent publication of the Centre, Development of National Technology Capacity for Environmentally Sound Construction, provides an in-depth analysis of the various environmental stresses caused by construction activities and a strategy for coordinated action by the industry, governments and professional bodies. This issue of the Journal includes an article, Sustainable development and the construction industry, which provides an overview of the on-going construction-environment debated. In addition to contributing to the environment debate, this issue of the Journal, like the previous issues, deals with a specific technical theme: roofing materials, by highlighting the experience of Kenya in fibre-concrete roofing technology. I hope that the efforts of UNCHS (Habitat) in disseminating technical information through this Journal will stimulate the professional community and encourage small-scale entrepreneurs to increase their efforts in producing and marketing the basic building materials required for shelter delivery in African countries and elsewhere. It is hoped that readers will find the articles included in this Journal of interest and useful in their professional work.

Elizabeth Dowdeswell
United Nations Centre for Human Settlements (Habitat)

Sustainable development and the construction industry

Women contribute significantly in the production of building materials


Sustainable development could be defined as “meeting the basic needs of human beings at present without compromising the requirements for socio-economic development of future generations”. It is a process of change, whereby technological processes, instruments, natural resources, and institutional arrangements are aligned, so as to create a potential for meeting the human needs both for today and tomorrow.

The process of socio-economic development and protection of the environment are not separate challenges. The sustainability of development cannot be ensured in a climate where growth plans consistently fail to safeguard the environment and arrest the degradation of the natural-resource base and the ecosystem as a whole.

The construction industry, which plays a significant role in economic development in every country, provides, on the one hand, direct means to the development and expansion of economic activities and, on the other hand, is a major consumer of the planet’s natural resources and a polluter of the environment.

The rapid increase in the volume and complexity of construction and the resource-demanding nature of modern technologies have imposed severe stress on the biosphere. Agricultural land is often lost through urbanization and also quarrying and extraction of raw materials used in the industry. Forests and wildlands are lost through conversion to other uses. Unsustainable use of forest timber for construction purposes and firewood for manufacturing lime or brick contribute to the loss of these valuable natural assets. Similarly the excessive use of fossil fuels in the construction and building-materials industries is threatening their limited reserves and, by their combustion, is contributing to the global warming extensively.

Industrialized countries are consuming natural resources at a pace that is unsustainable in the long term. Construction industries in these countries rely mainly on energy-intensive, high-temperature process industries producing steel, aluminium, copper, glass, cement, lime, ceramic etc. Vast amounts of energy are wasted through these processes which could be used through available heat-recovery methods. These industries are also major polluters of the environment through the emissions and dust that they produce through different types of firing processes. These and many other forms of environmental degradation caused by the construction and building-materials industries are not restricted to industrialized countries. For example, the excessive dependence of the building-materials industry on the use of firewood in developing countries, while causing deforestation, adds significantly to carbon dioxide emissions and the production of “greenhouse” gases.

While increased awareness and knowledge of the implications of resource depletion and environmental degradation caused by the building-materials industry have resulted in taking some action in the industrialized countries, the developing countries, particularly in sub-Saharan Africa, have made very little progress in arresting this situation. Their position is even more desperate given that many of them are faced with fragile environments, involving aridity, decertification, flood occurrences etc.

In the light of above scenario and through, mainly, international intervention and awareness-creation over the past few years, particularly after the adoption of Agenda 21 by the United Nations Conference on Environment and Development (UNCED) in June 1992, it has become clear that if sustainable development has to be ensured for future generations, the current trends and practices of the construction sector should be controlled and managed in a way that the natural-resource base is not depleted and the environment is not degraded irrevocably. The real challenge will, however, lie in ensuring this in a sustainable manner without reducing the rate of construction activities or bringing some of them to halt. What is needed is promotion of environment-friendly, clean and energy-efficient technologies and the creation of a favourable policy climate which would stimulate the sector to implement these innovative initiatives.

Agenda 21 underscores the importance of sustainable construction industry activities as a major contributor to the sustainable human settlements development and proposes a set of action plans for governments on how to manage activities in the construction industry to ensure its sustainability. (Section G (Promoting sustainable construction industry activities) of chapter 7 (Promoting sustainable human settlements development) of Agenda 21 is given in the annex of this article.)

This article provides a brief overview of the situation of the construction and building-materials industries as far as their sustainability is concerned, and seeks to generate some awareness among the actors involved in the sector. The article touches upon three major areas of concern namely:

(a) The deterioration of the physical environment (land, forests etc.) through construction activities;

(b) The depletion of non-renewable natural resources;

(c) The contribution of construction industry activities to the atmospheric pollution.

Construction of roof with more durable materials

Interested individuals are invited to refer to the publication, Development of National Technological Capacity for Environmentally Sound Construction, which is being published by UNCHS (Habitat) and will be released shortly. This publication, which represents one of UNCHS (Habitat)’s first significant steps towards implementing the recommendation of Agenda 21, provides a detailed analys of the concerns in the above-mentioned areas and proposes a strategy for a sustainable development of the construction industry.

A. Conflicts between the construction and building-materials industries and the deterioration of the physical environment

1. Land

The continuing growth of the human population and of industrial activities related to human settlements places an increasingly heavy demand on the world’s finite resources such as land, clean water and forests. Poor management and degradation due to human activities are placing a severe stress on the resources which, in some areas, has led to serious modification or depletion of the natural environment.

A fundamental requirement of sustainable development is that the harmful side-effects of the development process, particularly of construction activities, must not exceed or overload the assimilative capacity of the biosphere, so that the process of development can be sustained. The spontaneous and, often, uncontrolled pace of human settlements development in many developing countries, and even in some industrialized countries, makes it particularly difficult to control the attendant degradation of living conditions. For example, the increasing spread of human settlements into fragile eco-zones is rapidly destabilizing natural eco-systems in many developing countries. Occurrences of floods, landslides, mudslides etc., caused by construction on delicate hillslopes, wetlands etc., testify to the vulnerability of the environment to intervention by human activities (UNCHS (Habitat)).

The highly dispersed character of construction activities in most developing countries makes it difficult to monitor the physical disruption caused by construction. There is a growing concern, in many countries, about increasing land dereliction, caused by the quarrying of sand and gravel, extraction of brick clay etc. which ultimately reduces the available land for human settlements development. The degradation of the marine environment, caused by coral mining for the production of building lime, and the disruption of wildlife habitats and watertables, by excavations etc. are now attracting the increasing attention of physical planners and coast-conservation authorities (UNCHS (Habitat)).

Traditional roofing materials

Land-use conflicts are perhaps the main threat to environment in many developing countries. These conflicts arise largely because of the lack of coordinated national land-use policies. Each sector, such as mining and forestry, views the production areas as the best resource base for their development objectives. What follows is intense competition for the same areas, without a mechanism to prioritize competing uses.

In terms of using land for quarrying and extraction of raw materials, many national policies are more concerned with licensing exploitation and charging fees for revenue-collecting purposes. They are not concerned with the appropriateness of the use to which such land is put. For example, in Kenya, many key extraction areas are gazetted as National Parks or Forest Reserves, thus, directing the conflict in favour of wildlife or forest preservation but against the agricultural sector. Many areas have been licensed for clay or stone quarrying at the expense of the agricultural/livestock sector. Most of these actions have been carried out without conceptions of environmental planning or cost-benefit analysis. When political pressures increase, then the forests are again used to settle people in preference to wildlife conservation (P. Syagga, 1993).

Appropriate land-use policies and planning specially aimed at eco-sensitive zones are very often lacking in many developing countries. One of the main reasons for the lack of clear policies is that data on which to carry out environmental impact assessment and cost-benefit analysis are seriously lacking. There is, therefore, a need to collect data and devise appropriate methodologies for objective assessments upon which priorities for land use can be based. The assignment of priorities to alternative environmental needs is not a very difficult task to undertake, however, in the ultimate, the allocation of land-use priorities would involve an economic decision as between costs and returns and safeguarding the protection of the environment. Rational decision-making and implementation of appropriate strategies, that are transparent and effective, to solve the conflicts between land use and the construction and building-materials industries are urgent requirements which should be given high priority by decision-makers in many developing countries.

2. Forest resources

Forests are an important natural-resource base in any country, playing a crucial role in the conservation of watersheds, prevention of soil erosion and balancing the eco-system. Forests are also sources of domestic wood supply, woodfuel, buildings etc. and provide habitat for wildlife. Timber, as a major forest product, is not only a very crucial building material but is also very vital to the economies of a number of developing counties. Timber-producing countries gain considerable foreign exchange by exporting timber. Therefore, any loss of forests, for any reason, may provoke potential human, economic and environmental disasters.

The construction and building-materials industries contribute to the loss of forests by converting them to other uses. That contribute to loss of forests through non-renewable use of timber, bamboo and thatching materials, and the indiscriminate use of firewood to provide energy for building-materials production.

Timber, because of its superior characteristics and almost zero-energy content, has been one of the basic building materials for centuries. It has been extensively used both as structural members for buildings and bridges and also for decorative purposes. It is estimated that in the Philippines, the demand for wood in building construction is likely to rise from 173,000 m3 in 1990 to 433,000 m3 by the year 2000. In Indonesia, the demand for wood in housing construction is likely to exceed nearly 4 million m3. Japan imports 18 million m3 of sawn wood for the 1.5 million homes annually built there. In Chile, 60 per cent of the annual production of sawn timber is used in houses and other building construction (J. O. Siopongco, 1990). These figures mean that wood is going to be an essential building material both for modern structures as well as for traditional building construction in the years to come.

However, over the past several decades, there has been increasing concern about the destruction of the tropical forests and the adverse impact of this on the environment. Inefficient commercial logging operations, the use of wood as fuel etc. have resulted in deforestation in many regions. Managing the forests in a sustainable and environmentally sound manner so as to minimize the rate of deforestation is, therefore, imperative and should be given the highest priority.

More dependable roofing structure

One way of tackling the problems associated with deforestation is encouraging the use of commercially less-accepted species (CLAS) and industrial tree plantation species (ITPS). If properly managed and exploited, these species can serve as abundant and renewable resources of building materials that can be afforded by the vast majority of the population.

There are currently no significant examples of use of CLAS and ITPS as a walling material or roof-cladding material in developing countries. In some cases the wood elements are only restricted to internal partitioning.

The use of CLAS and ITPS for construction, especially for walling purposes and as shingles for roofing, is slowly showing potential in industrially-processed wood products where the CLAS and ITPS serve as raw material. The use of wood chips, pulps and excelsior for composite boards in some countries relies on timber species which are less suitable as sawn wood due mainly to their irregular form. There is potential for using chips and excelsior from CLAS and ITPS to manufacture wood-cement boards. In some countries, where these products are on commercial sale, there is an unfavourable market trend probably due to the unatractiveness of the finish of the boards.

The Second Consultation on the Wood and Wood Products Industry, organized jointly by UNCHS (Habitat) and UNIDO and held in Vienna in January 1991, underscored the importance of greater utilization, on a sustainable basis, of wood, including CLAS and ITPS, as a renewable source of indigenous building materials in housing and construction. The Consultation, while focusing on environmentally sound management of forests, devised a set of recommendations addressing the industry, governments and the international community on ways and means for popularizing the use of CLAS and ITPS in the construction sector. (For more information refer to the report of the Consultation mentioned in the volume 1, No. 4, of the Journal.)

B. Conflicts between the construction and building-materials industries and depletion of non-renewable resources

The construction and building-materials industries are major users of the world’s non-renewable resources. Apart from their share of fossil-fuel and tropical-timber use, the construction industry is a heavy user of several metals which have limited remaining exploitable reserves, such as lead, copper and zinc. Table 1 shows some data on the consumption, base reserves and base life index of some selected metals.

Table 1. Consumption and reserves of some metals


Consumption 1990
(thousand tons)

Base reserves 1990
(million tons)

Base life Index


17 878

24 500



10 773



Iron ore

925 000

229 000



5 544












6 973



Source: World Resources Institute, 1992.

The construction industry is responsible for the consumption of commercial energy in two principal ways: through the consumption of energy in the production of buildings and other constructed facilities, and through the consumption of energy in the subsequent use of these buildings and facilities. The energy in the production of buildings is used directly by the construction industry, whereas that consumed in buildings in use is controlled to a large extent by the eventual user. The design of buildings can also have a major impact on the intensity of subsequent energy use.

1. Embodied energy in construction

It has been found that the consumption of energy in the manufacture of building materials and components is about 75 per cent of the total energy requirement for the production of a building, the remaining 25 per cent being primarily used during on-site construction activities. However, in the context of developing countries, where construction activities are labour-intensive, the amount of energy required in construction is mainly used, in the manufacture and transporting of building materials. Therefore, economizing in the use of energy in the process of manufacturing energy-intensive building materials, such as lime, bricks, cement etc. and reducing the distance the materials need to be transported are more crucial in developing countries than in industrialized countries.

A high proportion of the energy used in the production of building materials is in a small number of key materials such as steel, cement, bricks, glass and lime. According to some analytical studies, the energy requirement for one square metre of corrugated iron sheet, fired clay tiles and fibre-concrete roofing tiles, for example, are 605, 158 and 46 megajoules respectively (UNCHS (Habitat), 1991).

Similarly, different types of construction systems (sets of materials) can result in considerable differences in the total embodied energy requirements in complete house systems. Table 2 shows a comparison of three houses in Argentina.

Table 2. Comparative energy requirements for three single-storey houses in Argentina lifetime to determine which is the optimum energy saving strategy.

House type

Embodied energy requirement (MJ/m2)

House made primarily with manufactured materials (hollow brick walls, concrete frame and roof)


House made partly with manufactured materials (clay brick walls, concrete frame, steel sheet roof)


House built primarily with local materials (adobe walls, timber frame, steel sheet roof)


Source: UNCHS (Habitat), 1991.

Because of the high energy intensities of many production processes, larger producers, using modern technologies (for example, cement producers) are aware of the need for energy efficiency. However, in the context of developing countries, where many of the producers operate at small-scale using traditional processes, it is unlikely that they can respond to changing pressure or alter established practices in a speedy manner. Any government policy should, therefore, focus on assisting the small-scale sector in upgrading its production technologies so as to economize on the use of energy in its daily operations. Such policies should include, among others:

a) Careful study and improvement of kiln operations;
b) Use of cheaper or non-premium fuels such as agricultural waste;
c) Use of solar energy and heat recovery devises in the kilns;
d) Reduction of transporting distances by decentralized production;
e) Use of recycled materials.

In addition to the methods and techniques for improving the energy efficiency of the production of building materials there is a major opportunity available by which to reduce the embodied energy of buildings; the appropriate choice of materials and design. Some strategies that designers can follow include:

a) Use of low-energy content materials;

b) Selection of lower energy structural systems, such as load-bearing masonry walls in place of reinforced concrete or steel frames;

c) Design of low-rise buildings;

d) Design for the use of materials, which are found near the site;

e) Use of, where possible, waste or recycled materials.

These strategies will not always be consistent with strategies for saving energy consumption in buildings. It is advisable to examine the total energy consumption over a building’s

Low-energy building materials

2. Energy in buildings in use

Energy is used in buildings for cooking, space-heating and cooling, and lighting and for productive activities. Studies show that in areas where there is a substantial annual heating requirement, coal-burning stoves are often used in urban housing: insulation standards in such housing are frequently very poor by comparison with those of industrialized countries, and the combustion products add considerably to urban air pollution. In areas where the primary need is for cooling, there is an increasing demand for air-conditioning in workplaces and upper-income urban households. Air-conditioning is inherently energy-intensive in relation to the cooling achieved: the poor insulation and sealing of many air-conditioned spaces add to the energy demand.

The use of improved insulation techniques for buildings and “passive solar” design approaches to reduce heating loads and/or eliminate the need for mechanical ventilation and air-conditioning are potential considerations for energy saving in buildings in use. Thus, strategies for greater utilization of these techniques must be formulated and enforced. In this regard, education of the designers, public awareness, demonstration buildings, revision of regulation etc. could be among the various tools and means to utilize this potential resulting in economy in energy use in buildings.

C. Contribution of the construction industry to atmospheric pollution

Pollution caused by construction and building-material-production activities include water pollutants from quarrying activities and effluents from chemicals, particulates from fuel combustion and manufacturing processes, carbon oxides (CO and CO2) from burning fuel, sulphur dioxide (SO2) and nitrogen oxide (NO and NO2) from high temperature burning, and hydrocarbons from the manufacture of chemicals and allied products such as paints.

At the local scale, the construction and building-materials industries create air pollution through emissions of dust, fibre, particles and toxic gases from site activities and building-material-production processes. They contribute to regional pollution through emissions of nitrogen and sulphur oxides in building-materials production, and they contribute to pollution on a global scale in two important ways: (a) by the use and release of chlorofluorocarbons (CFCs) in buildings contributing to the depletion of the atmospheric ozone layer, and (b) by the emission of carbon dioxide and other “greenhouse gases”.

Table 3 shows the annual carbon dioxide emissions from fossil fuel consumption and cement manufacture for four selected countries.

Table 3. Carbon dioxide emissions for selected countries, 1989, and the estimated contribution from construction, cement manufacture, and building use


Total CO2 production
(thousand tons)

Estimated proportion of CO2 output

Construction industry

Cement manufacture

Building use


118 157





651 936





641 398





5 192




Sources: World Resources Institute, 1992; and Wells, 1986.

An estimated 8 to 20 per cent of these emissions in different countries are due to construction and building-material-production activities, and a further 2.5 per cent globally results form the chemical reactions taking place in cement and lime production. World carbon dioxide emissions from fossil-fuel consumption and cement manufacture increased nearly four-fold from 6000 tons per year in 1950 to 22,000 tons in 1989 (Spence, 1993). A further enormous contribution to global emissions results from the energy consumption of buildings in use, up to as high as 50 per cent in northern industrialized countries (Spence, 1993).

Organic compounds, such as methane, make a considerable contribution to the greenhouse effect. A particular concern is felt in regard to CFCs used in insulation materials, in fire-extinguishing systems and in air-conditioners. Although the volumes of CFC emissions are low, they have a disproportionally high impact on climate.

Table 4 indicates the relative contribution made by the principal gases.

Table 4. Contribution to greenhouse warming by various gases


Contribution to warming

Carbon dioxide






Tropospheric ozone


Nitrous oxide


Source: Henderson and Shorrok, 1990.

Use of materials found near the construction site

As discussed in preceding paragraphs, most of the pollution resulting from building-material-production processes is the result of fossil-fuel burning. Therefore, the principal means of reducing pollution would be through increased energy efficiency in all activities. The transporting of materials is also major factor in contributing to the air pollution. Reducing the transporting requirements by decentralized production facilities will significantly reduce these emissions.

D. Concluding remarks

Previous sections have established that construction activities are causing, or contributing significantly to, many of the present processes of deterioration of the natural environment, in particular to:

· Loss of soil and agricultural land;
· Loss of forests, woodlands and wildlands;
· Increases in freshwater and coastal pollution;
· Increases in atmospheric pollution at local, regional and global scales;
· Depletion of the Earth’s non-renewable resources.

But continued and increasing levels of construction activity are essential to all aspects of development; and indeed only by raising living standards generally will it be possible to reduce or eliminate many of the currently most serious types of environmental deterioration. Poverty is one of the principal causes of both rapid population growth and land degradation and loss of tropical forests.

To ensure a sustainable future, it is, therefore, neither feasible nor desirable for the total level of construction activity overall to be restricted, although in the industrialized countries there may be strong arguments for reducing activity by re-using existing buildings rather than building new ones. In other cases, it is difficult to conceive of construction activity which does not result in some irreversible changes in the natural environment. Yet sustainable development does not need to imply a complete halt to irreversible change in the natural environment. Economists argue that one essential aspect of sustainable development is that the world’s total stock of “capital”, natural plus human-created capital, should not diminish over time.

Some conversion of natural into human-created capital is clearly acceptable within this definition. Construction of a dam, for example, reduces the existing natural capital of the region in many ways - through forest clearance, quarrying of construction materials, changes in water run-offs and sediment loads, changes in human and wildlife habitats and other ways - but it also creates a lasting asset, which can provide power, irrigation water and other benefits for the immediate future and, if well-designed, for a long time into the future. Similarly, the construction of housing and other buildings uses natural capital - through quarrying, land-conversion, the creation of atmospheric pollution and so on - but compensates for this by increasing the stock of human-created capital which will be passed on to future generations. The materials of which these fixed-capital assets are made are still available, though in a less useful form, for re-use in the future. Thus, human-created capital is intended to compensate for the loss of natural capital.

Given the nature of the construction industry, which is fragmented, multisectoral and rather complex in character, changes cannot be expected to happen in a speedy manner. However, all initiatives will involve change in technology, commitment towards preserving the natural resources, mitigating environmental degradation, and special investment programmes within the industry: but many of these inputs are unlikely to come about without a necessary stimulus from outside the industry. Therefore, communities, local and national governments, decision-makers, international agencies and any other actor involved in the construction sector should be committed to taking such measures as would ensure the sustainability of construction activities, so leading to sustainable social and economic development in all countries.


L. Henderson and L. D. Shorrok, Greenhouse Gas Emissions and Buildings in the United Kingdom, BRE Information paper 2/90 (Garston, Building Research Establishment, 1990).

J. O. Siopongco, “Greater utilization on a sustainable basis of wood including CLAS and plantation species as a source of indigenous low-cost building materials in housing and construction” (unpublished report prepared for UNCHS (Habitat), 1990).

P. Syagga, “Promoting sustainable construction industry activities in the African region” (unpublished report prepared for UNCHS (Habitat), February 1993).

UNCHS (Habitat), Energy for Building (Nairobi, 1991) (HS/250/91E).

UNCHS (Habitat), People, Settlements, Environment and Development (Nairobi, 1991).

J. Wells, The Construction Industry in Developing Countries (1986).

World Resources Report (World Resources Institute, 1992).


Basis for action

The activities of the construction sector are vital to the achievement of the national socio-economic development goals of providing shelter, infrastructure and employment. However, they can be a major source of environmental damage through depletion of the natural-resource base, degradation of fragile eco-zones, chemical pollution and the use of building materials harmful to human health.


The objectives, are, first, to adopt policies and technologies and to exchange information on them in order to enable the construction sector to meet human settlements development goals, while avoiding harmful side-effects on human health and on the biosphere, and, secondly, to enhance the employment-generation capacity of the construction sector. Governments should work in close collaboration with the private sector in achieving these objectives.


All countries should, as appropriate and in accordance with national plans, objectives and priorities:

(a) Establish and strengthen indigenous building-materials industry based, as much as possible, on inputs of locally-available natural resources;

(b) Formulate programmes to enhance the utilization of local materials by the construction sector by expanding technical support and incentive schemes for increasing the capabilities and economic viability of small-scale and informal operatives which make use of these materials and traditional construction techniques;

(c) Adopt standards and other regulatory measures which promote the increased use of energy-efficient designs and technologies and sustainable utilization of natural resources in an economically and environmentally appropriate way;

(d) Formulate appropriate land-use policies and introduce planning regulations specially aimed at the protection of eco-sensitive zones against physical disruption by construction and construction-related activities;

(e) Promote the use of labour-intensive construction and maintenance technologies which generate employment in the construction sector for the underemployed labour force found in most large cities, while at the same time promoting the development of skills in the construction sector;

(f) Develop policies and practices to reach the informal sector and self-help housing builders by adopting measures to increase the affordability of building materials on the part of the urban and rural poor through inter alia credit schemes and bulk procurement of building materials for sale to small-scale builders and communities.

All countries should:

(a) Promote the free exchange of information on the entire range of environmental and health aspects of construction, including the development and dissemination of databases on the adverse environmental effects of building materials through the collaborative efforts of the private and public sectors;

(b) Promote the development an dissemination of databases on the adverse environmental and health effects of building materials and introduce legislation and financial incentives to promote recycling of energy-intensive materials in the construction industry and conservation of waste energy in building-materials production methods;

(c) Promote the use of economic instruments, such as product charges, to discourage the use of construction materials and products that create pollution during their life cycle;

(d) Promote information exchange and appropriate technology transfer among all countries, with particular attention to developing countries, for resource management in construction, especially for non-renewable resources;

(e) Promote research in construction industries and related activities, and establish and strengthen institutions in this sector.

Means of implementation

(a) Financing and cost evaluation

It is roughly estimated that the construction activities of developing countries amount to about US$400 billion annually and will increase by about US$20 billion annually. The stream of new investments for these levels of activity and to bring in clean technologies is estimated at US$40 billion annually, primarily from private sources. If 10 per cent of the new investments come from the international community, this would amount to US$4 billion annually. About US$3 million would be needed to strengthen international organizations.

(b) Human resource development and capacity-building

Developing countries should be assisted by international support and funding agencies in upgrading the technical and managerial capacities of the small entrepreneur and the vocational skills of operatives and supervisors in the building-materials industry using a variety of training methods. These countries should also be assisted in developing programmes to encourage the use of non-waste and clean technologies through appropriate transfer of technology.

General education programme should be developed in all countries, as appropriate, to increase builder awareness of available sustainable technologies.

Local authorities are called upon to play a pioneering role in promoting the increased use of environmentally sound building materials and construction technologies, e.g., by pursuing an innovative procurement policy.

Kenya: Fibre-concrete roofing technology: Adaptation and progress*

* This report is produced on the basis of information and data given in an unpublished draft study prepared for the UNCHS (Habitat) by Martin Fisher and Mary McVay.

The vies and opinions expressed in this report are those of the authors and do not necessarily reflect those of UNCHS (Habitat). Mention of firm names and commercial products do not imply the endorsement of the UNCHS (Habitat).


In the previous issue of the Journal an article entitled “Stabilized soil-block technology adaptation and progress in Kenya” was included which highlighted the technological developments and adaptation processes of stabilized-soil blocks in Kenya and outlined the various block-making press manufacturing capabilities in the country. The role of Action Aid-Kenya (a non-governmental organization involved, among others, in rural development and promoting appropriate technologies for constructing schools and houses) was also elaborated.

The present report is the continuation of the report included in the previous issue but deals exclusively with fibre-concrete roofing-tile production-technology adaptation and progress in Kenya, again through the efforts of Action Aid-Kenya. Section A describes the history of fibre-concrete roofing-tile technology development and various promotional activities undertaken in Kenya, while Section B provides more technical information on different types of machines in use or developed and manufactured in Kenya highlighting their features and manufacturing processes.

A. History

The first known research on fibre-concrete roofing (FCR) was carried out by the Swedish Council for Building Research in Sweden in 1975. Later, in 1976, two researchers began their work at Kenyatta University Appropriate Technology Centre and at the University of Nairobi, Department of Engineering, with financial support from the Food and Agriculture Organization of the United Nations (FAO), the Swedish International Development Agency (SIDA), the Portland Cement Company and several local sisal plantation owners. They developed and field-tested a technique for making FCR sheets, but with rather disappointing results. Although, the laboratory test results were satisfactory, field production did not meet an acceptable standard, mainly, because the manual production process and the large size of the sheets made them weak and expensive. The sheets were manually compacted and in order to reach an acceptable strength they needed a cement to sand ratio of 2:1 and they still needed to be quite thick and carefully made. This led to a slow and expensive production process. Moreover, the large size and heavy weight of the sheets required a heavy and accurate roofing structure to prevent twisting and cracking. Installation was, thus, time-consuming and precarious. Nevertheless, the researchers and the organizations, involved in developing and testing FCR sheets pioneered the technology in Kenya and stimulated the initial interest in this technology.

In 1983, John Parry Associates, or Intermediate Technology Workshops (ITW), began to play a role in Kenya. Parry began research in 1977 in the United Kingdom with funding provided by the Overseas Development Agency channelled through the Intermediate Technology Development Group (ITDG). By 1983, he had developed a process of making FCR tiles using a battery-powered vibrating/screeding machine and a set of plastic moulds. While the concept of vibrating concrete to compact the mix is quite old, as are the general forms of the profiles Parry uses, his innovation was in the application of these practices to fibre concrete. Incidentally, a manual method of vibrating and moulding concrete tiles was developed independently in Malawi around the same time. Still Parry Associates was the first to bring such a machine to Kenya when, in conjunction with ITDG, they established the Intermediate Technology Workshop (ITW) in Nairobi to import machines, conduct training and manufacture tiles. By 1984, they had sold seven tile kits and assisted five businesses to get started.

In 1983, Action Aid-Kenya (AAK) purchased a Parry machine and sent one of its staff to United Kingdom for training. The plan was to test and disseminate FCR technology through AAK’s School Construction and Maintenance Scheme.

By September 1984, AAK had established four FCR tile-production units in Kiboswa, Kibwezi, Webuye and Kariobangi. These rather experimental production units were run by youth groups, trained and financed by AAK with the intention that, if the technology took off, they would become self-sustaining businesses. Meanwhile, they supplied AAK with roofing tiles for the schools, which served as a field test and promotional demonstration of FCR tiles. AAK also trained local artisans on how to roof with FCR tiles. This required drafting a manual with roofing specifications, a modification of the one produced by Parry, because of the generally low quality of timber available in Kenya compared with the timber in United Kingdom. The performance of the roofs was quite satisfactory and the scheme worked well in promoting the technology. There were, however, certain limitations, namely: the youth groups were not very cohesive, and had not as yet become mature enough to break away from AAK and become fully independent businesses; luck of financial-management and quality-control skills have been constant problems; in the early stages, technology being labour-intensive, required considerable training and supervision by AAK staff; and shortage of capable staff has limited the number of production units and the number of buildings roofed with FCR tiles.

Energy-efficient building materials

Nonetheless, the scheme, significantly, increased awareness of FCR tiles in Kenya and many entrepreneurs showed interest in buying machines and starting businesses manufacturing the tiles. However, in view of the rather high cost of Parry machines to be imported from United Kingdom, AAK began considering manufacturing FCR tile-producing machines locally to make them affordable for small-scale businesses.

1. Local technology adaptation

(a) Machines

In May 1986, AAK began to develop a manual FCR tile-vibrating machine to be produced in Kenya. The initial research and design work was conducted at the Housing and Building Research Institute (HABRI) of the University of Nairobi and the first product was a treadle-operated vibrating machine. After a field test with a work group of the National Council of Churches of Kenya (NCCK), the machine proved to be not efficient for operation by one worker. Therefore, AAK began to develop a two-person bicycle-powered machine (see Section B). A joint effort by AAK staff and an American missionary, who had begun work on an electric machine and on making FCR tile-moulds locally at HABRI, resulted in finalizing the designs of the manual and electric FCR tile-vibrating machines and a concrete FCR tile-mould production process. In early 1988, the first locally-produced tile-vibrating machines, which had been fabricated in Undugu Society’s Metal Production Unit, went on sale in Kenya. While Undugu Society is a charity, the Metal Production Unit operates as an income-generating unit. Its management has successfully demonstrated that good-quality tile machines can be made profitably in Kenya and sold at a reasonable price.

Meanwhile, HABRI also succeeded in designing a hand-cranked machine being sold by Hartz and Bell. Unfortunately, its performance has been quite unsatisfactory (see Section B). Moreover, Parry Associates responding to the competition introduced their own hand-cranked machine, but, at a higher price than those manufactured locally.

(b) FCR tile moulds, made in Kenya

Just as the imported machines were considered expensive, so were the imported moulds. In recognition of this, AKK and the American missionary developed a way of making tile moulds locally, from concrete. The technique, involving a series of moulds made from one original wooden “great-grand-mother” mould, was introduced to a local entrepreneur which manufactures the moulds.

(c) FCR technology: progress

FCR technology adaptation in Kenya, is still in an early stage, therefore, it is difficult to quantify its progress in terms of the number of buildings roofed with FCR tiles - or even in terms of production units established. However, all indications show that FCR tiles are taking off at a rapid pace, and that the potential market is extensive. This rapid expansion appears to be a direct result of the locally-available low-cost equipment and training.

ITW equipment was purchased in a package including: vibrating machine, 200 moulds, batch boxes and miscellaneous equipment, for Ksh. 130,000. However, an AAK machine plus 200 concrete moulds and the same miscellaneous equipment was about Ksh. 15,000 (both July 1989 prices) This means that the former requires a high-income entrepreneur possibly selling his assets or trying to get a bank loan; whereas the latter can be easily gathered from savings and family loans. In addition, since, the local machines, equipment and moulds may be purchased separately, the investment can be made gradually, which is most appropriate for a small-scale entrepreneur.

People are already taking advantage of the new opportunity. Up to November 1988, after several years in Kenya, ITW had sold 43 kits. In 1988 alone Undugu Society had sold 68 machines, over 50 per cent more, and by March 1989 Undugu had sold another 24. The majority of these machines have been sold to the private sector. Purchasers are given a brief manual on tile-making and are invited to attend AAK training when they are ready to begin production. However, some begin production without training and the actual number of businesses started is difficult to determine.

In March 1989, AAK mailed out a brief survey to ITW and customers in an attempt to try to assess the progress and needs of FCR tile producers. Although the initial respondents were few (20) some conclusions were as follows:

(a) People generally became aware of the technology through magazines, newspapers and technology shows. Others heard about it via the institutes promoting it (AAK, ITDG, ITW, HABRI), or visiting producers and buildings;

(b) Businesses with ITW equipment required around Ksh. 150,000 vis-is AAK businesses which needed Ksh. 50,000;

(c) People promote their tiles via:

(i) Demonstration buildings;

(ii) Advertisements (signs, leaflets, samples in shops);

(iii) Approaching builders on sites, or trying to get contracts;

(d) Customers inclose institutions, wealthy individuals, and lower- to middle-income people. This illustrates FCR’s competitiveness with both galvanized corrugated iron sheets and other tiles. This means that the potential market for FCR tiles in Kenya is substantial;

(e) Producers are, generally, not producing at full capacity and expressed concern about:

(i) Lack of awareness on FCR tiles, particularly by institutions, large contractors and government officials;

(ii) Problems of marketing in general: the strategy that should be used and how to finance it;

(iii) Lack of working capital - most produce tiles on orders, but customers prefer manufacturers to have tiles in stock, ready to buy;

(iv) People are not satisfied with the red-oxide colouring - it gets a white film and also fades quickly;

(f) There are wide discrepancies in cost analysis, indicating that financial issues need more attention during training, as do marketing strategies;

(g) Most people conduct some quality-control procedures, including physical examination of tiles, making recommendations for the roof structure and often inspecting the roof as it goes up. However, without site visits, the general quality of production is difficult to assess;

(h) Many producers received second-hand or no training at all, except written guidelines. This is clearly a major problem, as all promoters of the technology feel that inadequate training will result in poor-quality tiles which, at this early stage, could ruin the reputation of the technology;

(i) So far, producers have few complaints about the performance of the machines, nor have they reported receiving complaints on the quality of their tiles or roofs.

Thus, it seems that the machines and tiles are performing well. However, as increased awareness and the availability of a cheaper machine has sparked rapid expansion in the number of machines in the market, measures are being taken to ensure proper dissemination of the technology. In particular, this means increasing and improving training programmes, establishing better coordination between trainers and producers, and addressing the issue associated with quality control. Currently, official standards are being written and the establishment of an FCR Tile Association is being considered to address these and other issues.

(d) FCR training

AAK’s FCR tile-production training differs from ITW’s training in that it is half theory and half practical, whereas ITW’s is almost fully practical. In view of the complex management involved in FCR tile production, and, since, building a specific type of roof structure for the tiles is rather complicated, AAK feels that it is necessary to spend more time on understanding these issues, rather than concentrating fully on tile production. In addition, since, the quality of the tiles depends a great deal on labour it was found prudent to explain the reasons, e.g., why tiles need to be vibrated for 45 seconds and why it is better to cure them in a tank for 10 days, rather than simply instruct trainees to do so.

The course consists of, first, demonstrating the raw-material processing, vibration, curing, and quality control, and secondly, roofing specifications and the calculation of the number of tiles needed for various sizes and pitches of roofs etc. The FCR tile business-management course goes over costing and pricing of tiles and roofs and also marketing strategies. For promotional purposes, participants receive colourful advertising pamphlets which illustrate the advantages of the tiles, contain technical data on roofing specifications and show an easy format for estimating the cost of an FCR-tile roof.

(e) Standards and specifications

One major barrier confronting the promotion of FCR tiles is the lack of public acceptability of this product. AAK currently chairs a committee established by the Kenya Bureau of Standards, to establish official standards and specifications for FCR tiles. Without official recognition, the municipal council cannot include FCR tiles in building codes, and structures with FCR cannot be legally built in towns. However, once standards are issued, the public will see the legitimacy of FCR tiles and will have an idea on their quality.

Women trained in FCR-tile factory

(f) FCR-tile technology transfer

The transfer of the FCR-tile technology developed by AAK to other African countries has already begun on an informal basis. But AAK is planning to establish a regional appropriate technology unit to meet the rising requests for training in these and other technologies, and to establish more systematic and effective ways of disseminating the technology regionally.

(g) FCR tiles in the United Republic of Tanzania

FCR-tile production with AAK machines and moulds has already started in Arusha and Mwanza, United Republic of Tanzania. In both cases the Roman Catholic Church purchased machines from Undugu. In the case of Mwanza, the Church sent a group for training with AAK in Webuye, but in Arusha training was conducted by a volunteer, who was trained in Kenya. In United Republic of Tanzania, the demand for FCR tiles is quite high, as galvanized corrugated-iron sheets are not readily available and are very expensive. The Roman Catholic Church in Arusha has already imported a number of Undugu bicycle-type vibrating machines and established some units to produce tiles commercially.

(h) FCR-tile technology in Uganda

An independent missionary involved in designing the electric tile-vibrator in Kenya, in 1987, travelled to Uganda to conduct a training on tile-making for Action Aid-Uganda, for the United States Agency for International Development (USAID) in various cooperatives, and for churches. The missionary took three electric vibrators with him, one, of which went to Action Aid-Mityanna. Since then, AA-Mityanna has imported quite a number of machines, but was at a standstill when they requested a visit from AAK in 1988. They were not certain on how to proceed with a technology-dissemination programme for tiles, and, more immediately, they have not been taught how to make ridge moulds. The informal style of the training they received was, thus, problematic.

Meanwhile, USAID endeavoured to fabricate AAK-designed tiles and machines locally. It imported the necessary metal for fabricating machines in Gulu Metal Co-operative, assisted by Euro Action-Accord. Two people from Gulu, in Northern Uganda, visited the Undugu Society’s Metal Production Unit for training and returned to Uganda, designs in hand. However, due to the informal training and lack of follow-up, they have, yet, to produce a satisfactory machine.

In Uganda, as in United Republic of Tanzania, while things have progressed to a certain level, the problems of lack of training and local mould and machine production have not been fully solved. Owing to the AAK’s tied commitments in focusing efforts on its own target areas, regional requests for training and information were not responded properly. However, there are now plans to expand Action Aid-Kenya’s technical training facilities not only for Kenya, but for the East and Southern African sub-region.

Tiles ready to be put on building roof

B. Fibre-Concrete Roofing Tile Technology


This section gives some description on FCR-TILE technology. It explains the theory of vibration, the critical factors involved in designing an FCR-tile machine, provides some information on FCR-tile equipment available in Kenya and gives a detailed description of the AAK-designed FCR-tile machines and tile moulds.

1. General principles

FCR tiles are thin screed, sand and cement roof tiles with a very small percentage of natural fibre added to the mortar mix. The wet mortar is laid on a flexible plastic sheet and it is compacted into a thin flat screed by a vibrating table. The compacted flat screed is then lifted on to the plastic sheet and laid over a tile mould which gives it the desired shape. It stays on the mould to dry for a minimum of 12 hours before it is demoulded for another 12 hours of drying and then placed in a water tank for curing for a minimum of 10 days. Finally, the tile is removed from the water and allowed to dry for an additional 10 to 14 days before it is ready for use.

The function of the fibre in the tiles is to help stop the formation of cracks during the initial manufacturing and drying stages. During these stages, the mortar is still wet and weak. The fibre is stronger than the wet mortar and can hold it together to prevent bending and shrinkage cracks. After the tile is fully cured, the mortar is strong enough and the fibres no longer contribute significantly to the tile’s strength. It is only the fact that tiles with fibre may have fewer micro cracks than tiles without fibre that makes the tiles with fibre somewhat stronger.

In fact, if care is taken during the forming process and if the hardening of the mortar is carefully controlled, so as to minimize shrinkage cracks, use of fibres would not be necessary.

Other factors which contribute to the strength of FCR tiles include the following:

(a) The sand used should be clean, sharp and well graded river sand;

(b) The sand and cement must be well mixed in dry condition using a proportion of three measurements of sand to one of cement by weight;

(c) The mortar mix must be kept fairly dry;

(d) The vibration/compaction must be adequate;

(e) The initial drying must not be too fast; and the time for curing and final drying must be adequate.

All these steps must be taught to the operator in a training course on the production site. However, the effectiveness of the compaction by vibration is to a large extent dependant on the vibrating machine used.

2. Compaction by vibration

Builders have used vibration as a means of compacting concrete mortars for over a century. Starting, simply, with the tamping of a concrete form, and ranging to the use of portable poker vibrators and the use of large vibrating tables for compacting precast concrete components. Vibration of a wet mortar acts to compact the mortar into a flat screed and to remove any excess air bubbles and water from the mix. It thus, ensures that after drying and curing the product will have a minimum of voids or air pockets and will, as a result, be much stronger.

FCR tiles which were not vibrated would require a much higher percentage of cement in order to be of the same final strength as those which are vibrated.

Physically, the vibration causes compaction of the mix by slightly shifting the position of the particles, allowing gravity to pull them into a tighter configuration, making the screed more dense and compact. The effectiveness of the vibration is directly related to the acceleration which it imparts to the mortar particles and to the number of oscillations (the duration of the vibrations in a given time). Up to a point, the longer the vibration time the more compact the mortar. It should be noted that too much vibration can lead to a separation of the mortar by particle size and weight and this can actually cause the tile to become weaker.

The acceleration is equal to the amplitude of the vibration times the frequency of the vibration squared. However, too large vibration amplitudes will cause the mortar particles to jump off the table instead of just shifting slightly. Generally, the amplitude should be less than 1 or 2 mm of motion. Good compaction is, thus, best achieved by vibrating at a high frequency with a low amplitude.

The very limited experimental results available indicate that it is the product of the acceleration times the duration of the vibration that determines the degree of the compaction. Approximately, equivalent compaction was obtained in one ninth the time when the frequency was tripled (the acceleration, which is proportional to the frequency squared, was increased by a factor of 9). Experiments also indicate that both a vertical and horizontal component of vibration are necessary for effective compaction. In particular, the vertical component is most effective for knocking down and spreading out the pile of mortar when it is first place on the table while the horizontal component is most effective for compacting the mortar after it is already spread into a thin screed.

Women tile producers in Kenya

3. FCR-tile vibrating machines

(a) Methods of vibration

A vibrating table, which, in most cases, is mounted on springs or rubber mountings, can be made by using a number of different mechanisms. It can be impacted by a hammer which will cause vibrations at both the impacting frequency and also at higher frequencies (the natural frequencies of vibration of the table top). It can be driven by a direct connection to a rotating motor or wheel giving vibrations at the frequency of the rotation. It can be driven electro-mechanical by fixing a magnet to the table with a stationary electrically oscillating coil around it. And, it can be driven by a rotating eccentric cam mounted on bearings fixed to the bottom of the table and driven either through a flexible linkage by a motor also mounted to the bottom of the table.

The last two options, electromechanical or a rotation eccentric cam, have the advantage of a minimum of wearing parts: and the last one has the added advantage that it can be easily adapted to either an electrically- or manually-driven mode. This is the mechanism of vibration chosen by both John Parry in his designs and by AAK. The amplitude of the vibration is determined by the product of the mass and the eccentricity of the rotating cam and also by the mass of the table top and the stiffness of the mountings.

The energy required to vibrate a table is also a function of the table’s mass and properties of the mountings.

An effective and energy-efficient eccentric-cam vibrating devise should have a light weight, yet stiff table-top mounting on either very stiff springs or stiff rubber mountings. In general, the eccentric cam should be lightweight and the eccentricity should be quite small. However these factors have to be adjusted to match the weight of the table top and the properties of the mountings.

(b) Critical factors for design and analysis

The following factors must be considered when designing or analysing any FCR-tile vibrating machine.

Frequency of vibration: As discussed above, the higher the frequency the more effective the vibration and the less time it will require to compact the mortar.

Mode of operation: Is it operated electrically or manually, and what is the most appropriate mode of operation for a given location of use?

Strength: What loads will it be subjected to during use and during transport, and is it designed so that it can withstand these loads without breaking? Are any of the moving components likely to wear out after a short time or are they all properly designed for a long life?

Ease of use and maintenance: Is it easy to use? How many operators are required and how strong do they have to be? How easy is it to maintain? Are spare parts locally available?

Ease of manufacture: How difficult is it to manufacture? Are any special skills or tools required? Are all the components locally available or do they have to be specially imported?

Cost: Is it affordable for members of the target group to buy? What is the pay-back time period?

4. FCR-tile machines in Kenya

(a) Parry electric and manual machines

The first FCR-tile machines in Kenya were the original models of the Parry Associates (ITW) electric tile vibrators. These vibrators have a rotary eccentric cam which is mounted between two ball bearings inside a small metal box which is bolted to the bottom side of the table top. The cam is driven through a flexible linkage (made out of a small-diameter plastic hose pipe) from a small 12-volt fan motor.

The 6-mm thick aluminium table top is mounted on four stiff rubber bearings which are, in turn, mounted on the top of a sheet-metal box which houses the 12-volt motor. The 6-mm-thick metal tile frame hinges at the back of the table and locks down in the front. The lock handles hang below the table top and are pivoted from it on 6-mm-diameter machine screws.

These vibrators are manufactured by Parry Associates in United Kingdom and quite a number have been imported by Kenyan FCR-tile manufactures.

Parry’s newest version of the vibrator is the plastic encased “multivibe” unit which clamps onto the bottom of a 4.5-mm steelplate table-top, mounted on four rubber mountings.

By 1987, Parry had developed a hand-operated vibrator which is operated by two people. The crank turns a set of reduction pulleys which are connected by two V-belts and which drive the eccentric cam through a flexible linkage at close to 40 revolutions per second (the same frequency of vibration as the electric machines). Although the hand-operated machine seems to work just as well as the electric machine, reports from the field indicate that it is quite tiring to use.

(b) HABRI hand cranked machine

The Housing and Building Research Institute at the University of Nairobi designed a low-cost manually-operated tile vibrator and arranged for it to be manufactured by Hartz and Bell in Nairobi. HABRI has used these machines in some of their training and has arranged for some field-testing by various organizations including Canadian Save the Children in Meru.

As with the other FCR-tile machines available in Kenya, the vibration is caused by a rotating eccentric cam, mounted on the bottom side of the vibrating table top. The driving mechanism uses the hand crank, gears and gear housing from an Indian-made hand-powered grinding wheel. This mechanism turns a 6-inch diameter pulley which in turn uses a V-belt to drive a 3-inch diameter pulley mounted on the same shaft as the eccentric cam. Thus, the eccentric cam rotates about 25 times for each rotation of the hand crank. The hand crank, therefore, has to be turned at high speeds to get effective compaction.

The machine is designed to be operated by a single operator who concurrently turns the crank and screeds the mortar to make tiles. This requires a very awkward motion and makes it rather difficult to operate.

Reinforcement of FCR tiles

(c) AAK FCR-tile machines

This section describes the main design features of the vibrating table-top which is used in all three of the AAK-designed machines: the treadle, bicycle, and electric machines. Although some of these features are similar to those on the Parry machines, most of the design decisions were made based on the locally-available resources or in order to make machines compatible with local requirements.

As with the Parry machine, the vibration of these tables is caused by a rotating eccentric cam mounted between ballbearings on the underside of the table top. This cam is connected to the power source by a flexible linkage.

The size of the tile screed was chosen to be 250 mm by 500 mm and either 6- or 8-mm thick. This is the same size as tiles from the Parry machine. The reason for this was that by early 1986, when work on these machines began, there were already a number of tile producers in the country using Parry equipment. Thus, rather they introducing a competing tile size, it was decided to design machines to make tiles compatible with those already on the market. Later that same year, the Kenya Bureau of Standards (KBS) Technical Committee on FCR tiles, decided to standardize the size of FCR tiles in Kenya to the same nominal size of 250 x 500 mm.

The table top is made from 4.5-mm thick mild-steel plate. (Parry has recently also switched from 6-mm-thick aluminium to this material on his latest model.) The rubber mountings are the mountings used for the air cleaner of a Peugeot 504 which are readily available in Kenya. These rubber mountings are attached by nuts with spring washers to small stall mountings made from pieces of 50 x 25 mm hollow sections. The steel mountings are, in turn, bolted by two 8-mm diameter machine screws and nuts to the underside of the table. This arrangement avoids any problems of stripped screw threads and is, generally, a robust design.

The tile frame is hinged at the back of the table as on the Parry machine and is locked down by two locking handles on the front. These handles are welded to large-diameter machined bushings which pivot on 20-mm diameter shafts. These short shafts are bolted by two 8-mm diameter machine screws to the underside of the table. This is a much stronger design than other machines where the locking handles are pivoted on single 6-mm diameter machine screws.

The eccentric cam is mounted inside a piece of 2” x 3” rectangular hollow section which is bolted by four 8-mm diameter machine screws to the underside of the table. Machined bushings are used to mount the two sealed ballbearings. The shaft for the cam is 16 mm in diameter. The flexible linkage is made from a length of fibre-reinforced plastic tubing and is held in place by two standard screwed hose clamps.

On all the AAK machines, including the electric one, the vibrating table is mounted on a framework made from rectangular hollow-steel sections. These are also much stronger than the sheet metal and flat-bar frameworks used by other machines.

The weakest part of the table-top design is probably the mounting of the eccentric-cam bearings and the eccentric cam itself. Although the bearings are large enough and will last a long time, there is still too much machining and too many nuts and bolts involved in the way they are mounted. Also the eccentric cam is only held in place by a small set screw which is liable to come loose in time. If it is not kept tightened, it can come loose and cause a reduction in the vibration frequency.

(d) AAK manually-operated FCR-tile machines

AAK works in many remote parts of the country. In these areas it is difficult to recharge a battery every week as is required for electric machine. Thus, it was decided that AAK’s first priority should be to design a manually-operated machine. This section explains the various methods of producing vibration manually and describes in detail the method chosen for use on the AAK-designed machines.

As discussed in the previous section, the effective compaction of mortar requires a high frequency of vibration. The imported machines vibrate at about 40 cycles per second, and it was decided that to be competitive, a manually-operated machine should vibrate at about the same frequency. However, a person can comfortably turn a handle, operate a lever, or otherwise move for extended periods of time at a rate of around only one cycle per second. Thus, the problem of designing a manually-operated tile vibrator is really one which converts a human motion of one cycle per second into a vibration of not less than 40 cycles per second.

A number of methods were considered for producing this 40 to 1 multiplication in frequency. These included: using a set of gears; using two sets of pulleys and V-belts, each with a 6 to 1 reduction as was also used by Parry for his manual vibrator; using a flexible belt to run a small pulley off a bicycle or other large-diameter wheel, as is often used on manually-operated sewing machines and knife sharpeners; and using a multi-stage adaption of the rope-driven slip-drive mechanism in which a small roller-wheel is driven by friction from a rotating bicycle wheel and its tyre.

In this last option the small roller-wheel is mounted between two fixed ball-bearings, it rests on top of a standard 26” rear bicycle wheel and tyre, and when the wheel rotates, the roller is driven by friction at a much higher rate. The small-roller is then connected by a flexible linkage to the rotating eccentric cam which causes the vibration. This option has a number of advantages over the other options considered. It does not require any difficult or expensive components such as gears, V-belts, pulleys, flexible drive belts or special elastic and nylon cords. In fact, only common bicycles parts and ball-bearings are required, which makes it fairly cheap and easily repairable by village bicycle repairers. It can easily reduce rotation frequencies from 15 to 20 times the frequency of the bicycle wheel, and is easily adaptable to a handle, treadle, or pedal-drive mechanism.

Tile-production factory in a rural area

Its major disadvantage is that, like any drive system, it is prone to energy losses. The main losses in this system are due to the flexing of the bicycle tyre, friction in the bearings, and occasional slippage between the tyre and the small roller-wheel. It is difficult to assess the quantity of these losses, but if the bicycle tyre is kept well inflated and if the bouncing of the small roller-wheel is kept to a minimum the losses should not be very great.

Nonetheless, early experiments showed that the frictional losses caused the vibration to stop within seconds of stopping the power input to the bicycle wheel. This meant that to keep the vibration going; the bicycle wheel had to be powered almost continuously. In order to solve this problem, two 175-mm diameter flywheels were mounted on the same shaft as the small roller-wheel with one on either side of the wheel. These act to store the energy and, thus, allow the cam to continue rotating up to 5 or 10 seconds after the wheel is no longer powered. Thus, the wheel can be powered less frequently and more easily. In order to avoid expensive machine costs, the fly wheels are made from cast-iron plough-wheels which are first statically balanced by drilling holes in them to reduce any unbalanced weight.

Another problem encountered during the machine’s development was that the bicycle tires available locally are not very round. Thus the small roller-wheel needs to be able to move up and down to compensate for the changing tyre radius. Therefore, the roller and two fly-wheels are mounted on a hinged member. It was originally hoped that their weight would be enough to stop them from bouncing on the bicycle wheel, but it was found that they need to be held down with a spring. Unfortunately, this extra force increases the energy losses due to the tyre flexing and makes the bicycle wheel somewhat more difficult to turn.

(e) AAK treadle operated FCR-tile machine

The idea behind the treadle-drive machine was that a single person could both operate the treadle, to cause the vibration, and at the same time screed the mortar to make the tile.

The vibrating table top was mounted at waist level on a framework made of 40-mm square hollow sections. A standard rear bicycle wheel, sprocket and freewheel were mounted just behind the table top with the top of the wheel some 75 mm below the level of the table top. The small roller-wheel was 35 mm in diameter and was mounted in between the two ball-bearings of a standard bicycle bottom bracket in such a way that it could roll on the bicycle tyre. The two fly-wheels were mounted on the same shaft which was connected by a fibre-reinforced plastic linkage to the eccentric cam. A bicycle chain was hung over the freewheel sprocket with one end connected to the mainframe by a flexible spring and the other end connected to the free end of a treadle. The treadle was a metre in length and was pivoted at a point just to one side and behind the place where the operator stood.

When the operator pushed down the treadle with his/her foot, the chain caused the sprocket and, thus, the bicycle wheel begun to rotate, which in turn rotated the small-wheel, fly-wheels find the eccentric cam. When the operator’s foot was lifted, the spring returned the treadle to its original position. The freewheel allowed the sprocket to reverse its rotation on the upstroke without reversing or slowing the rotation of the bicycle wheel.

Because of the small diameter roller-wheel and the long treadle lever, the eccentric cam would rotate approximately 38 times each time the treadle was pressed. Thus, if it was pressed once every second, the vibration frequency was approximately 38 cycles per second.

In laboratory tests, the treadle operated machine worked well and made good tiles. However, from the initial field test with a youth group, it was determined that it was somewhat difficult for a single operator to coordinate his of her hands and feet when making tiles, and to exert the required effort to make the tiles. As a result the tiles tended to be weak due to too little vibration.

This encouraged AAK to try and redesign the vibrator to be operated by two people, with one providing the vibration and the other screeding the tiles. Although this option requires an additional worker, labour is not very expensive in Kenya. By providing this extra job the cost of a tile only increases by 6 or 7 per cent.

The field test also demonstrated that bicycle bottom bracket ball-bearings are not suited to the high rotational frequencies of the small roller-wheel. They required frequent greasing and continually became loose in their housing.

(f) AAK pedal-powered FCR-tile machine

This machine is very similar to the treadle-operated machine except that the bicycle wheel is driven by a standard bicycle chain, chain wheel and pedals replacing the treadle. Two operators are required, one to pedal and the other to make the tile.

Again, the vibrating table top and the bicycle wheel are mounted on a framework made of 30 mm square hollow sections. A demountable drive assembly with pedals, a chain-wheel, a bicycle seat and handlebars are bolted to one side of the framework. It is positioned so that the operator faces the table top when pedaling. The whole machine can be levelled by screwing in or out its six adjustable feet. The chain-wheel and pedals rotate in a standard bicycle bottom bracket which can be moved back and forth on the frame of the drive assembly to adjust the tightness of the drive chain.

The small roller-wheel is 50 mm in diameter and is gnarled to give a better grip on the tire. It is mounted on a 20-mm diameter shaft between two sealed pillow block ball-bearings with one fly-wheel mounted on either side. This bearing and the wheel sub-assembly is pivoted from above and pressed against the tire by a compression spring.

Since there is a reduction in diameter between the main chain-wheel and the freewheel sprocket, each time the pedals are turned the small roller-wheel rotates almost 38 times. So if the operator pedals at a rate of one revolution per second then the vibrating frequency will be 38 cycles per second.

Women carrying finished tile

The pedal-operated vibrator worked well in field tests making up to 250 tiles per day with five workers, and over 50 machines were sold in the first year and a half of production. The machine was sold for Ksh 8500 (July 1989 price). In general, the idea of a manually-operated machine is well received by customers who see the advantage of not using a battery and of providing more jobs. However, they find the price somewhat high and the machine too large to transport easily.

(g) AAK electric FCR-tile machine

The main problem with making an electric tile machine is the availability of a 12-volt motor. A convenient motor to use, and one which works at the appropriate rpm, are the motors used for the interior cabin fans in automobiles. Technically, these are the same motors used in the imported machines, but in Kenya new motors of this type are usually unavailable or prohibitively expensive. However, second-hand fan motors can be bought very cheaply from junk yards around Nairobi. Many of these motors are in very good condition because, in general, people in Nairobi do not use the interior fans of their cars very often.

The main body of the electric machine is made of 40-mm square hollow sections welded into a rectangular framework and then covered by a sheet of metal. The rubber mountings of the vibrating table top are bolted directly on to the hollow sections and the motor is mounted on a piece of sheet metal welded between the hollow sections. The whole machine is substantially stiffer and stronger than the imported machines. Four 6-mm thick metal tabs with 12-mm holes in them are welded to the bottom of the machine and can be used to bolt the machine to a workbench. An electric switch is mounted on the sheet-metal cover and two wires with cable clips are used to attach the battery. Over 100 of these machines were sold by the Undugu Society in the first one and a half years of production and so far very little trouble has been reported.

The biggest problem is the electric switch. It is very difficult to buy good-quality electric switches in Kenya and the best ones available, still, tend to break down quickly. This is also a problem with the imported machines and it just means that the user will have to be a bit careful and be willing to install a new switch every once in a while.

(h) FCR-tile moulds

The most crucial design features of any FCR-tile mould include the following:

Shape: Determines the type of tile manufactured. Most FCR tiles are of the pantile shape, but recently interlocking and “Roman”-shaped tiles have been introduced by Parry Associates and are now made in Kenya.

Alignment mark: The tile moulds must have some type of marking so that the mortar screed can be placed on the mould in the correct position and alignment. If the screeds are not properly aligned on the moulds, then the tiles will be skewed and will not lie on the roof properly.

Weight: Tile moulds should be reasonably lightweight. They have to be moved around the site during tile production and if they are too heavy this will become a problem.

Stacking mechanism: With over 200 moulds at any manufacturing unit, there should be a method of stacking the tile moulds so that they do not occupy too much space. Also the wet screeds must be kept out of the sun and wind so they do not dry out too quickly and crack. Thus, it is useful to have a stacking method which protects the tiles from these elements.

Strength: Each mould is handled several times a day, and they should be strong enough to withstand the stresses.

Cost: Since about 200 tile moulds are required to start a production unit, it is important that their unit cost should remain quite low.

Moulds for ridge tiles are usually made from marine plywood. They are “V” shaped with the angle fixed according to the pitch of the roof. Some have been made using hinges at the bottom so that the angle can be easily changed for differently pitched roofs.

Small-scale production of FCR tiles

(i) Parry FCR-tile moulds

Parry Associates manufacture and sell hot-pressed plastic tile moulds. These lightweight tile moulds are made in United Kingdom and sell for Ksh 350 each in Kenya (July 1989). The moulds are mounted on wooden frames and they stack on top of each other in such a way that the freshly formed tiles are protected by the mould above from the sun and the wind.

In order to ensure that tiles are correctly placed on the moulds, the moulds have a small protruding ridge which has to be very carefully aligned with the bottom edge of the tile. However, the ridge is rather small and is difficult to see because it gets covered up by the plastic sheet.

In 1984, Parry licensed a local Nairobi fibreglass manufacturer, Sai Raj, to manufacture and sell fibreglass tile moulds. These are of a very similar design to the plastic moulds, but are in general heavier and stronger than the plastic moulds. However, at about Ksh 200 each (July 1989) they are still very expensive for many small-scale producers.

In order to avoid these high costs, many of the first groups to produce tiles in Kenya (including the AAK groups on the suggestion of ITW) made their own tile moulds by filling a plastic Parry mould with mortar to form solid concrete moulds. These were then mounted on simple wooden frames so that they could be stacked. However, these solid moulds are too heavy and the surface is usually quite rough.

(j) AAK concrete FCR-tile moulds

In October 1986, an American missionary, started working with HABRI at the University of Nairobi on designing locally made FCR-tile moulds. HABRI came up with the idea of thin screed concrete moulds, cast from a single solid wooden mould which was called the “grandmother mould”. The idea is to cast a number of thin screed (15 mm thick) “mother moulds” from the grandmother mould and then to use them to cast thin screed “tile mould”. The top surface of the mother mould is a direct negative of the grandmother mould’s top surface and thus the top surface of the tile mould would be an exact replica of the grandmother moulds.

These tile moulds are made from a manually compacted mix of two measures of sand to one of cement. They are about 600 x 350 x 13 mm and they weigh around 5 kg each. Their cross-sectional shape is the same as that of a tile with an additional flat section added on either side. The junction between the place where the tile lies and the flat side section forms a sharp edge which runs along the whole length of the tile mould. It can be easily felt through the polythene paper and this allows the alignment to be accurately performed.

The moulds are designed to be stacked in simple wooded racks with the flat sections on the sides of the moulds resting on thin wooden runners. Each rack holds about 40 moulds and is covered with a polythene sheet to protect the moulds from wind and sun. These moulds are also reinforced for strength by two ribs which are formed across their bottom surface. These ribs also act as handles allowing the moulds to be easily pulled in and out of their stacking racks.

The main problem with the original manufacturing method was the expensive and time-consuming process of manufacturing the solid wooden grandmother moulds. However, later it was determined that the grandmother mould could also be made from concrete by the introduction of a wooden-framed “great-grandmother mould”. This mould consists of a rectangular wooden box which has no top or bottom and which is bolted together by two bolts at each corner. The box is made of one-inch thick hard wood, and the top edges of the two ends are cut to have the exact profile of the tile mould.

To make a grandmother mould the “great-grandmother” box is placed on a flat table and it is filled with a dry mortar mix of two measures of sand to one of cement. A very straight and stiff metal angle-iron is then held across the two ends of the box and is moved back and forth and up and down along the end profiles of the box to shape the mortar into the shape of the two profiles. It is crucial to use a very dry mortar mix (to avoid any slumping) and to keep the angle-iron parallel to the sides of the box at all times. This step, the making of the grandmother mould, only has to be done once at any given site, but it is vital that it is done perfectly. Nonetheless, the wooden great-grandmother is much easier to make than a solid wooden grandmother mould. One has simply to trace the tile profile on to the two pieces of 1 -inch by 6-inch hard wood, cut them out carefully, make the other two sides of the box and proceed as above. In this way it is easy to make tile moulds of almost any shape including tapered moulds which have a tighter curvature at one end. To date the technique has successfully been used to make moulds for pantiles, interlocking tiles and the tapered “Roman”-type tiles following the same basic patterns as those introduced by Parry Associates.

Once the grandmother mould is made and cured for five or six days, it should then be placed back inside the box, then, be oiled with old motor oil and the box (great-grandmother mould) should be lifted up by 25 mm by placing a piece of wood under each end. It now forms a 25 mm high frame around the edges of the concrete grandmother mould. This frame is filled with mortar and the same angle-iron straight edge is used to compact the mortar into a 25 mm thick screed.

The newly-formed mother mould is left to dry on the grandmother mould for 12 hours before it is removed and put into a water tank to cure for seven days. Thus, only one new mother mould can be made each day. After a mother mould has been fully cured and dried, it is oiled with old motor oil, and a 13-mm-thick metal frame which has been formed to have ends with the same shape as the moulds is placed on to the mother mould. This frame is filled with mortar which forms a tile mould by using the same angle-iron straight edge. Two strengthening ribs are added on the back side of these moulds. After 12 hours on the mother moulds, the tile moulds are demoulded and placed in a water tank for a day or two. They are then removed and the top surface are painted with a thin mix of cement and water to fill in any holes and to smooth out the surface.

Loading of finished tiles

With one grandmother mould, one mother mould can be made per day. The number of tile moulds that can be made per day is equal to the number of mother moulds available. Thus, starting with a great-grandmother mould, it takes 35 days of producing mother moulds and tile moulds before 200 tile moulds are made and ready for use. If a mother-mould kit, which consists of five mother moulds, a metal frame and angle-iron straight edge, is used, it takes 45 days before 200 tile moulds have been made and are ready for use.

These tile moulds are being manufactured and sold by a private entrepreneur in Nairobi who sells them for Ksh 23 each. He also sells the mother mould kits at Ksh 1000. The cost of materials for making moulds is about Ksh 8 per mould. (All prices are based on July 1989 quotations.)

Zimbabwe: Low-income housing pilot projects


UNCHS (Habitat) has been assisting the Ministry of Public Construction and National Housing (MPCNH) of Zimbabwe since Independence in 1980 in developing and implementing appropriate housing policies, programmes and projects for low-income families in both urban and rural areas. This article highlights the unique features and achievements of two low-income housing pilot projects, one in an intermediate urban centre of Kwekwe and the other in a rural growth centre of Gutu.


A new post-Independence national housing policy

The pre-Independence housing policy was geared towards segregated development in the urban and rural areas. Housing for the indigenous low-income workers in the urban centres was provided mainly through overcrowded rental dormitory-type hostels with shared sanitary facilities. Housing for the majority of the population in rural farming areas was not provided and it was left to the individual low-income family to build traditional huts of mud and thatch with inadequate sanitary facilities.

With the achievement of Independence in 1980, the housing problem was reviewed within the context of national socio-economic transformation to meet the goal of growth with equity throughout the country. Home-ownership in both the urban and rural areas was introduced to provide security of tenure as the basis for the improvement of housing conditions. Three modes of house construction, namely aided self-help, building brigades and housing cooperatives, were brought in to replace the conventional private contractor mode of construction. Housing standards were revised to meet the socio-economic needs of the low-income families so as to provide decent shelter at affordable costs. A new rural housing programme for villages, resettlement schemes, communal lands and growth points was launched for the first time in the country’s history to provide shelter for the majority of the population.

Providing practical solutions to low-income housing problems in Kwekwe and Gutu

Need for pilot housing programmes and projects

In order to develop and test the new housing polices and programmes, the Government of Zimbabwe, through the then Ministry of Local Government and Housing, approached the United Nations Development Programme (UNDP) to provide preparatory technical assistance by the United Nations Centre for Human Settlements (Habitat). This preparatory assistance request resulted in a project and a number of recommendations on housing options and standards. As a follow-up to the recommendations of this project, a report proposing two experimental low-income housing projects and community-development programmes was approved which resulted in the detailed planning, programming and implementation of the first two low-income housing pilot projects in Kwekwe and Gutu in November 1982.

Description of the projects


The objectives of the pilot projects in Kwekwe and Gulu were to test and monitor the following:

· New planning, design and construction solutions which attempt to achieve a closer match between the specific functional requirements of the lower-income beneficiaries and their financial capacities;

· New methods of organization in aided self-help, cooperative and communal efforts, including building brigades, which would enable the beneficiary groups to be involved more closely in the achievement of their own housing solutions through participation in the design, finance and construction stages of housing and community development;

· The possibility of expanding domestic thrift potential for low-income home finance through the establishment of new loan institutions (such as building societies) geared to the small loan requirements and savings capacity of low-income beneficiaries;

· The suitability of these new solutions for replication in future national housing programmes.

Selection of the sites

The selection of Gutu and Kwekwe as sites for two pilot schemes was made after careful consideration of several possibilities. Gutu, the district centre under the local authority of the Gutu District Council, is considered to be one of the most rapidly-expanding rural growth centres in Zimbabwe. Its residents include a large number of low-paid wage-earners and self-employed people who are in urgent need of acquiring their own houses. The location of the site in Gutu has special significance because it was selected to link Gutu and Mupandawana, centres that were separate prior to Independence. Kwekwe, under the local authority of the Kwekwe Municipal Council, on the other hand, is a typical example of an intermediate urban centre, with several mining and related industries. Most of the lower-income families are employed by the major industries or provide support services for these industries.

Project components

The major physical components of the projects in Kwekwe and Gutu comprise the essential elements for housing development programmes. These consist of:

· 1045 serviced plots or stands of 300m2 (12 m x 25 m) in Kwekwe and 199 serviced plots of 400m2 (14m x 28m) in Gutu, planned around cul-de-sacs and P-loops;

· Infrastructure services to each stand with individual water supply, sewerage, access and bus roads, stormwater drains, security (tower) lighting and electricity;

· Building-materials stores to supply building materials to project beneficiaries during house construction stages and later to be converted into primary-school classrooms;

· Provision of sites for future community facilities such as shops, markets, churches, day-care centres, schools etc.


A number of major achievements, which make the pilot projects unique, have enabled the Ministry of Public Construction and National Housing and the two local authorities to strengthen their capacity to develop low-income housing projects. Since the beginning of the projects, all the above-mentioned objectives of the project have been realized over a period of three years. Some of the significant achievements resulting from these projects are as follows.

Local bricklayers, carpenters and plumbers are employed to build houses

Layout design outline for aided self-help in Kwekwe

Aided self-help is the most popular choice of the majority of beneficiaries in Kwekwe and Gutu

Choice of modes of construction

The three modes of construction, i.e., aided self-help, building brigades, and housing cooperatives, provide a range of construction options to low-income households to suit their income levels, savings, skills, and availability of time to build their own houses.

The aided self-help construction mode implies a high degree of self-reliance on the part of the beneficiary, with limited technical assistance provided by the project staff. Building brigades consist of qualified and experienced carpenters, bricklayers and plumbers, who are employed by the local authorities to build houses. They are non-profit organizations whose aim is to provide skilled labour to those beneficiaries who do not have adequate time to build their own houses. Housing cooperatives, which are guided by basic principles of open and voluntary membership, are aimed at meeting the needs of their members through collective efforts and the pooling of human and financial resources.

Aided self-help has been found to be the most popular choice selected by almost 100 per cent of the beneficiaries in Kwekwe, while in Gutu 69 per cent of the beneficiaries selected the aided self-help mode, 24 per cent selected building brigades of the local authority and 7 per cent formed a housing cooperative. The aided self-help mode has the lowest cost especially in terms of labour, since the labour costs are higher by about 10 per cent in the case of cooperatives and about 50 per cent in the case of brigades which have higher overhead costs. However, each of the three modes of construction is cheaper than the conventional private contractors; assists in enhancing the building skills of the project beneficiaries and local small-scale builders; and generates employment at the local level.

Community participation

The project beneficiaries have been involved closely in the achievement of their own housing solutions through participation in the design, construction and finance stages of the housing development process. The site layout plans, the house design options and the choice in the modes of construction provided housing solutions which aimed at a close match between the specific functional and social requirements of the low-income households and their financial capacity. The new planning and sub-division of plots based upon cul-de-sacs and P-loops not only provided an efficient and cost-effective plan for infrastructure services but also provided a departure form the rigid grid-iron sub-division plans used in the past, thus responding to the local socio-cultural and physical conditions. Individual families selected their house plans from a range of house-design options, including room sizes and layouts, to meet their specific social, functional and economic needs. Since the majority of the beneficiaries selected the aided self-help mode of construction, they actively participated in the supervision and construction of their houses. In these tasks they were aided by community development officers and building promoters, who provided on-site advice and supervision.

Role of women

Women played a significant role in the pilot projects in Kwekwe and Gutu. They gained training and experience in community participation, learnt how to set up and manage credit facilities, participate in the design and construction of their homes, and availed themselves of employment opportunities in and around the project areas. For the first time, housing allocation criteria were revised and designed to consider heads of household regardless of sex. Thirty-six per cent of the household heads in Gutu and 20 per cent in Kwekwe are women. All are either wage-earners or self-employed supporting their families, and yet earn less than the median income.

Project beneficiaries are closely involved at every stage of planning and construction

Thirteen women, together with one male household head, formed the first housing cooperative in Gutu. The woman chairperson, who took the leadership role to mobilize the group, is a self-employed vegetable seller in the nearby market like the other members of the cooperative. Furthermore, it was a common sight to see women with their babies on their backs transporting building materials in wheel-barrows, in the tractor/trailers provided by the project, or by hand, and others mixing concrete, laying blocks and supervising construction.

Joint public and private sector financing

The pilot projects are the first example of joint public and private-sector financing for low-income housing in Zimbabwe, involving one of the three building societies which have mainly financed middle- and high-income housing in the past. An innovative housing-finance mechanism geared to small loan requirements and savings capacity was introduced to mobilize the domestic thrift potential of low-income households. The public sector, through a grant from the United States Agency for International Development (USAID), provided the capital cost for land and infrastructure development while the Beverly Building Society provided the capital cost for building-materials loans.

The low-income project beneficiaries also mobilized their skills and savings in the construction of houses. These, together with the loan-repayment guarantee from MPCNH, provide the necessary collateral for the mortgage. Furthermore, the basic principles of affordability, minimum standards and full cost recovery have been applied in the finance mechanism. In Kwekwe, for example, the average infrastructure cost per stand (plot) was about Z$1250 and the average building loan for a four-roomed core house of 50 sq m was about Z$2350 with a total average capital cost if Z$3600 per house, which was to be recovered over a period of 25 years at an interest rate of 9.75 per cent for infrastructure and 12.5 per cent for building loans. Based upon this, the average monthly repayment including service and supplementary charges was about Z$33, which was about 27.5 per cent of the income of a household earning Z$120 per month, i.e., below the median income of Z$150 per month. (The quoted figures are based on 1985 rates).

Supply of building materials

In order to reduce the cost of construction and to provide an easily accessible supply of building materials, the building loans to the beneficiaries are in the form of building materials available at the on-site store. This store is managed by a store manager and assistants as part of the site team. Most of the materials have been procured through competitive tendering for bulk supplies to reduce costs and achieve economies of scale. The materials production brigades of the two local authorities supplied building blocks and other concrete products manufactured at the small decentralized production units near the project areas. A stores system using kardex cards, receipts, and accounts cards, and which can operate both manually and using a microcomputer, has been specifically developed to ensure the efficient delivery and dispatch of building materials and to keep stock of materials and the building-loan accounts of the project beneficiaries. Most of the beneficiaries used materials supplied from the stores but a few used their own materials procured through friends and relatives.

Building materials are accessible at on-site stores

Training and support communication

After the selection and verification of the applicants, one-day weekend workshops on the housing process were organized both in Kwekwe and Gutu. The aim was to provide a comprehensive orientation regarding the various aspects of the project and the role of various people involved, including the beneficiaries. Audio-visual aids, including video films, exhibition of plans, models, building manuals and information sheets, were used during the workshops to supplement the discussions held with the groups of 50 families in each workshop. Furthermore, on-site training and advice was also provided as a follow-up by the building promoters and the community development assistants.

In addition to the training and support communications for the beneficiaries, the local project staff, including the staff of local authorities and the Ministry, were trained before the commencement of the project, through an intensive three-week group course on project implementation and management. Furthermore, MPCNH staff involved in the project execution also benefitted from UNDP/UNCHS (Habitat) fellowships for in-service training to attend short-term workshops and course organized by UNCHS (Habitat) and other institutions outside Zimbabwe. All these efforts have been helpful in strengthening the institutional capacity at the community, local and national levels.

Multilateral co-operation

The pilot housing projects have been a joint multilateral cooperation venture of MPCNH, UNDP and UNCHS (Habitat). As mentioned earlier, USAID and the Beverly Building Society have provided financial support. In addition, the two local authorities, in Kwekwe and Gutu, together with the project beneficiaries, have played a significant roles in the implementation of the projects. At the time of writing about 95 per cent of the houses had been completed.

Process and replicability

Monitoring and evaluation

One of the objectives of the pilot projects has been to test and monitor the suitability of the new housing solutions for replication in future national housing programmes and projects. This has been achieved through the use of necessary monitoring and evaluation instruments. The joint MPNCH/UNCHS/UNDP Project team has been monitoring the projects’ progress through weekly/fortnightly review meetings and monthly site visits and meetings to ensure that the work plan for implementation is adhered to. Monthly progress reports have been prepared to monitor the problems experienced and actions taken. Furthermore, routine tripartite review meetings between the Treasury, MPCNH and UNDP/UNCHS (Habitat) have been held to review the project at the policy level.

Impact on on-going housing projects

Even before the final completion and evaluation of the pilot projects, the initial approaches and findings from these projects have had several effects on on-going projects in other urban and rural areas, which are funded by MPNCH and/or funded with other multilateral or bilateral donor agencies such as USAID, the World Bank, the Commonwealth Development Corporation (CDC), and the Government of Italy. Such donor-funded projects, amounting to about US$130 million, were implemented in different parts of the country on a similar basis to the pilot projects and are thus gaining from the experience accumulated from the new housing solutions attempted in Kwekwe and Gutu.

Replicability in future housing programmes

The lessons learned, the experience gained and the policy feedback from the pilot projects have established a significant base for the replication of the new housing solutions and achievements in future national housing programmes and projects. The Government of Zimbabwe, through MPCNH, has already received preparatory technical assistance from UNCHS/UNDP and US AID to prepare a feasibility study to establish the Zimbabwe Housing Development Corporation (ZHDC), which will be the major housing agency to enable the implementation of such projects in future. Furthermore, UNCHS (Habitat) has also provided preparatory technical assistance together with the Overseas Development Administration of the United Kingdom to establish a Building Research Institute in Zimbabwe, which, amongst its other activities, will be involved in future pilot housing programmes and projects.

Cross-section of one of the house-types

Possible development from a basic core house

Diversity of urban form

India: Technology profile: Solar timber seasoning kiln*

* Submitted by Central Building Research Institute (CBRI). Roorkee, India.


Solar energy could easily be used in air-seasoning of timber. Much heat is however, lost by radiation from the surface that absorbs it. It could be utilized more effectively if the heat energy could be entrapped inside a chamber. In this way, continuously transmitted heat is available for the drying process. This can be achieved by preparing a chamber with transparent glass plates. Such a kiln has been designed in the Central Building Research Institute, Roorkee, India (see figure 1). It consists of three main parts, viz., (a) solar-energy collector, (b) seasoning chamber, and (c) chimney.

Black-painted galvanized-iron sheeting of 22 SWG is used as solar energy collector. With the help of a wooden frame, a transparent glass sheet is fitted around the collector leaving an air gap of 5 cm for the movement of fresh air. It is attached to the bottom of the south wall of the seasoning chamber at an angle of 30° with the horizon.

A double-wall chamber is constructed with transparent glass except for the north wall which is of brick masonry. Black-painted aluminium fins of 24 SWG are fitted in the east, west and south walls at an angle of 45° with the horizon. The roof is made of black-painted corrugated galvanized-iron sheeting and has a slope of 1 in 3.

To provide a stack effect inside the seasoning chamber, a chimney (30 x 30 x 80 cm) is fitted vertically over an opening provided in one of the corners of the roof of the seasoning chamber.

Performance of the solar kiln

Performance of the solar kiln was studied in India by seasoning various species of wood, e.g., mango (Mangifera indica), haldu (Adina cardifolia), deodar (Cedrus deodara), teak (Tactona grandis), jamun (Eugenis jambolana), shisham (Dalbergia sissoo) and sal (Shorea robusta).

The seasoning of mango, jamun and haldu timber was carried out in the months of August and September. The time taken in seasoning from green stage to 10 per cent moisture content for the above three of thickness 3.75 cm in the solar kiln was found to be 17, 27 and 18 days respectively while in the shed it was 35, 62 and 40 days. Teak, deodar and shisham timber was seasoned in the month of February and March and the thickness of the planks was 5.0 cm. The time taken in seasoning by the respective woods in the kiln was found to be 20, 14 and 28 days while in a shed they took 42, 25 and 60 days. Sal wood is considered highly refractory from a seasoning point of view and is generally used in the form of scantling. Therefore, the size taken for study was 7.5 x 15 cm and the study was carried out from November to January. It was found that in the kiln it took 67 days while in the shed the seasoning was completed in 4 months. On average, it can be concluded that the time taken for seasoning in the kiln was about half of that taken in air seasoning.

The high temperature inside the kiln helped in lowering its relative humidity. However, in the initial stages it was somewhat more than the prevailing atmospheric relative humidity due to a quick decrease of moisture content. During rainfall, the moisture content of the plank kept inside the shed increased due to high relative humidity of the atmosphere. However, in the kiln there was no appreciable change as the entry of fresh air was prevented. The maximum difference of temperature inside and outside the kiln was 15°C.

Normal practice in air-seasoning is to keep the timber without proper stacking on an uneven platform in the field or under a tree or shed. In these situations the material cannot be protected properly from sun rays and rain showers and neither can the direction of air flow be regulated. Thus no proper air-seasoning can be achieved in this manner, besides the increase in time of seasoning. The seasoning losses such as warping, cracking or shrinkage are also high in such a situation and sometimes the material is not of any use except as fire wood.

Capacity and cost of construction of a solar kiln

The kilns designed in India were of two different capacities, viz., 3 and 15 cubic metres of wood. The cost of construction of the smaller kiln is about US$ 1600 while that of the larger one is about US$4200 (1989 price quotations).

Publications review

Published by UNCHS (Habitat)

Earth Construction Technology

Earth is one of the main materials used for shelter construction in most rural low-income settlements of developing countries and also in urban ones. Under these circumstances, earth construction has often been characterized by dilapidated, temporary and unsafe structures. In fact, living examples of good, durable and attractive earth buildings are hard to come by, while the popularity of the material has dwindled to the extent that, even in circumstances where it should be the obvious choice in rural housing construction, preference has been given to relatively modern materials.


In principle, soil is not restricted to low-cost construction, but, rather, forms the basis of a technically sound engineering practice which is comparable to concrete technology or that of any of the popularly adopted building materials. The issue of earth being a low-cost material is incidental and, indeed, an added advantage to these technically viable properties. For this reason, the material should be promoted alongside other conventional materials to the extent that professionals in the construction sector can make a choice for earth in preference to or as an alternative to comparable materials. It is along these lines that the objectives of wide-scale adoption of the material could be achieved while meeting the construction needs of low-income people.

Following this principle, earth construction faces an obvious disadvantage in comparison with other popularly adopted materials. There is only limited knowledge of good earth-construction practice. The construction technologies which are predominant in the informal channels for artisan training are defective and inappropriate. In the conventional technical and professional training institutions, there is hardly any coverage of the subject of earth construction apart from basic civil engineering considerations.

This publication covers a range of practical information and knowledge on different aspects of earth construction including: (a) Basic principals of earth application; (b) Design and construction techniques; (c) Surface protection; and (d) Production of components. The publication concludes with a comprehensive bibliography which would be useful for those who wish to acquire further knowledge and reading material on the subject.

200 pp., HS/265/92E: ISBN 92-1-131 192-5

National Design Handbook Prototype on Passive Solar Heating and Cooling of Buildings

Since its inception, UNCHS (Habitat) has been actively promoting energy conservation and the more efficient use of energy in human settlements. The process of producing electrical energy, which is practically the main from of energy supplied to buildings, is, unavoidably, very inefficient. The overall efficiency of electricity production, from the power station to the consumer, is little more than 20 per cent. Hence, for every unit of electrical energy that is saved in a building, up to five times that value is saved in the power station in terms of primary energy. In order to reduce the consumption of electrical energy in buildings, passive solar heating and natural cooling are two important means which lead to financial benefits without reducing the required comfort in buildings. This publication covers a number of areas with regard to energy in buildings such as fundamentals of passive solar architecture, fundamentals of heat flow, basic design principles and strategies, final design evaluation etc.

162 pp., HS/182/89/E: ISBN 92-1-131105-5


Human Settlements and Natural Disasters

Human settlements are frequently affected by natural disasters - earthquakes, floods, hurricanes, cyclones - which take a heavy toll on human lives, destroy buildings, and infrastructure and have far-reaching economic and social consequences for communities and countries. The vulnerability of human settlements to natural disasters is continuously rising due to the concentration of population and economic activities in large agglomerations and the precarious situation of low-income settlements in both urban and rural areas.

In many developing countries, characterized by heavy a concentration of population, shanty towns, slums and marginal settlements, a disaster can lead to serious consequences even where the initial impact of the disaster is not very severe. The most common of such repercussions of disasters are characterized by cyclone-flood-contamination-epidemics continuum. It is this possibility of a chain reaction that has led researchers and policy-makers to the conclusion that a successful disaster prevention and mitigation programme necessarily involves a complex set of inter-dependent measures ranging from physical planning to crisis management.

This publication is based on the Centre’s concept that although natural disasters cannot always be prevented, their effects can be reduced through a variety of measures, such as better construction standards, the definition of high-risk areas and activities of high vulnerability, improved land use, and the design of buildings and infrastructure systems to minimize their vulnerability.


Examples are given of pre-disaster and post-disaster projects implemented by the Centre, with a view to illustrating some of the measures available to mitigate future disasters. The aim is to foster a greater disaster awareness and to enable disaster-prone countries to learn from each others’ experience.

40 pp., HS/156/89E: ISBN 92-1-131080-6

Building-related Income Generation for Women - Lessons from Experience

Over the past several years UNCHS (Habitat) has been examining the existing and potential contribution of women to national development, through their participation in the improved functioning of the human settlements sector. One important aspect of this is the role that women play and have the capacity to play in the construction industry. The involvement of women in the construction industry varies greatly from country to country, but very few countries have recognized the full range of possibilities for drawing on women’s skills as building artisans and entrepreneurs.

In most countries, the building industry has traditionally been male-dominated, and women have considerable difficulty in gaining access to trade training and in obtaining skilled jobs. Particularly in the developing countries, women are usually limited to the poorest-paid tasks, and they are severely discriminated against in attempts to improve their status. Yet, in those countries where women have been given the opportunity to compete on an equal footing, they have shown that their work is as good as that of any craftsman and that they are capable of undertaking most of the tasks performed by their male counterparts.


This report is intended to highlight women’s needs in training and job-placement in the construction industry and to suggest ways in which affirmative action can be taken to overcome the barriers traditionally faced by women in obtaining construction-industry employment.

40 pp., HS/197/90E: ISBN 92-1-131115-2

Global Strategy for Shelter to the Year 2000 - GSS in Action

This publication has been written for all those who are interested in ways, means and modes to improve the shelter sector in their own countries: policy-makers, entrepreneurs, researchers, community leaders - in short, men and women looking for a more habitable world. It illustrates practical applications of the principles of the Global Strategy for Shelter to the Year 2000 (GSS).

The first part offers, for the reader who is not familiar with the Global Strategy, an overview of the main recommendations of that document. The second part, which forms the main section of the publication, consists of 22 success stories from 17 countries. They highlight one or more recommendations from the Strategy and show how they were implemented through various programmes and projects. The third part includes practical suggestions on how to initiate a national shelter strategy. The last part describes the various actions taken by governments around the world to study, formulate, implement or complement their national shelter strategies.


To facilitate shelter for all by the year 2000 is not a dream, it is an ambitious but realistic goal. It can be met if countries persist in their efforts to house their citizens, with courage, conviction and perseverance, using all the available tools of an enabling environment.

105 pp., HS/249/91E: ISBN 92-1-131172-1


UNIDO/UNCHS (Habitat) First Consultation on the Construction Industry, Tunis, Tunisia, 3-7 May 1993

The First Consultation on the Construction Industry was organized jointly by the United Nations Industrial Development Organization (UNIDO), and the United Nations Centre for Human Settlements (Habitat). It was hosted by the Government of Tunisia in cooperation with the Technical Centre for Building Materials (CTMCCV) and brought together 175 participants from 41 countries (18 from the African region) and six international and regional organizations. The Consultation was inaugurated by His Excellency Dr. Hamed Karaui, Prime Minister of Tunisia.

The Consultation analysed the current situation of the construction industry in developing countries and made an examination on the mechanisms for balanced growth between the formal and informal sectors. It also made proposals on strategies and policies for the promotion of the sector and identified some cooperation projects and investment opportunities aimed at developing national capacity in the construction industry.

An important objective of the Consultation was to promote sustainable construction-industry activities - an area of expressed concern in Agenda 21. In fact, this was the first global event since the United Nations Conference on Environment and Development (UNCED) held in Rio de Janeiro in 1992 to address the challenges and opportunities in introducing environmentally-sound construction practices in developing countries. In this regard, the Consultation, among other issues, focused on three key areas of sustainability namely: (a) the management of non-renewable resources; (b) the control of physical disruption; and (c) the minimization of air pollution caused by construction-related activities.

Finally, the consultation agreed on a comprehensive set of recommendations on the following issues:

(a) Prospects for development of the construction industry in the developing countries;
(b) Promoting sustainable construction industry activities.

These recommendations and a summary of presentations and discussions will be incorporated in the report of the consultation which is in preparation.

Regional Workshop on the Production and Utilization of Local Building Materials in Eastern and Southern Africa, Lusaka, Zambia, 20-21 May 1993.

The two-day Workshop, organized by Shelter-Afrique in conjunction with the Ministry of Local Government and Housing of Zambia, brought together more than 40 participants from nine countries and a number of international and non-governmental organization as well as Zambia-based institutions and UNCHS (Habitat).

The Workshop which had the objective of promoting the production and use of local building materials through the exchange of views and experiences amongst the main actors in this industry devised a set of recommendations to governments and the international community on how to improve the performance of the sector. As part of an immediate action, the participants recommended that governments, NGOS, and international organizations should establish steering committees at the national level to coordinate activities and disseminate information on local building materials.

During the Workshop several issues of the Journal of the Network of African Countries on Local Building Materials and Technologies and some other UNCHS (Habitat) publications relevant to the subject of the Workshop were distributed among the participants and a detailed informative presentation was made on the Networks’ aim and its activities.

The Urban Management Programme: African Regional Workshop, Nairobi, Kenya, 11-15 January 1993

The first African Regional Workshop on Urban Management, which was held in Nairobi, brought together about 100 urban management experts from some 20 sub-Saharan African countries.

Since the aim of the Workshop was to initiate the process of regionalization of UMP in Africa, the following issues were discussed: (a) Which political and institutional changes are necessary in order to resolve the crisis of urban management in African cities? (b) What contribution can UMP make towards the economic and social development of African cities? (c) What are the principal objectives of UMP regionalization and, in this context, how can this group of experts contribute towards this process?

The participants joined in three working groups with simultaneous sessions. Each group addressed all three issues. These groups were assisted by members of the UMP team of experts from UNCHS (Habitat) and the World Bank as well as a consortium of experts provided by the Overseas Development Administration (ODA) of the United Kingdom.

The Workshop recognized that UMP is helping to initiate a fundamental process of transformation and change through the improved management of African cities. In order for this process to be effective, it has to go hand-in-hand with democratization, decentralization, acknowledgement of human rights and social justice, popular participation and gender responsiveness. The crisis in which many African cities find themselves today compels UMP to help reinforce local authorities and community-based organizations (CBOs) while bearing in mind the need for strengthening the fundamental functions of government.

The Workshop recommended that UMP should provide support regarding the following priority areas at local, national and regional levels:

(a) Urban land management;
(b) Urban infrastructure management;
(c) Municipal finance and administration;
(d) Urban poverty alleviation.

Finally the Workshop adopted the “Nairobi Declaration” on a number of urban management issues.

Forthcoming events

Workshop of the Network of African Countries on Local Building Materials and Technologies, Nairobi, Kenya, 6-8 September 1993

In reviewing the activities of the Network, the medium-term plan (1992-1997) of the United Nations Centre for Human Settlements (Habitat) has stressed the need for expanding its (the Network’s) coverage and for a shift in focus from information exchange to increased collaboration in actual implementation of specific field activities. The urgency for consolidating the gains from the on-going collaboration and the need to seek new initiatives for strengthening the domestic capacity of African countries in the production of building materials has also been underscored by the United Nations New Agenda for African Economic Recovery and Development in the 1990s (UN-NAAERD), through its emphasis on regional and sub-regional cooperation. In the light of the emerging needs of the countries in the region a critical review of the activities of the Network should provide a useful framework for improving the effectiveness and widening the coverage of future collaboration. The Workshop will provide an opportunity for such a review and for the formulation of an action-oriented programme that could be implemented through the Network.

The Workshop, organized by UNCHS (Habitat), will bring together senior policy-level government officials from about 15 African countries and representatives from a number of United Nations and other international and non-governmental organizations. The objectives of the Workshop will be:

(a) To develop a strategy for improving the effectiveness and coverage of the Network;

(b) To establish a framework for launching a programme for domestic capacity-building through strengthened Network activities in the building-materials sector.

Each country participant is invited to prepare a response paper addressing a number of issues related to the building-materials sector in their respective countries and present them to the Workshop.

It is expected that the Workshop will devise a set of recommendations on how to strengthen the Network and how to launch a programme of domestic capacity-building in the building-materials sector in sub-Saharan Africa.

For more information contact UNCHS (Habitat), P. O. Box 30030, Nairobi, Kenya.

First National Seminar on the Promotion of Production of Local Building Materials and the Performance of the Construction Industry, Nairobi, Kenya, 12-15 October 1993

This National Seminar will be organized by the Ministry of Public Works and Housing of the Government of Kenya in collaboration with UNCHS (Habitat). The Seminar will bring together policy-makers, professionals and manufacturers from both public and private sectors to review and appraise the performance of the building-materials and construction sectors in Kenya and propose recommendation on ways and means of promoting them in a sustainable manner. The Seminar is expected to provide an opportunity for the Government of Kenya and the private sector to deliberate on the recommendations of the recently concluded Workshop of the Network of African Countries on Local Building Materials and Technologies. It will also establish a framework for closer cooperation between the Government and UNCHS (Habitat) for implementing the activities of a planned regional programme on domestic capacity-building in the building materials sector in sub-Saharan Africa.

For more information contact the Ministry of Public Works and Housing, P. O. Box 30260, Nairobi, Kenya, or UNCHS (Habitat), P. O. Box 30030, Nairobi, Kenya.


PO Box 30030 Nairobi, KENYA. Telephone 621234
Cable UNHABITAT; FAX (254)-2-624266/624267; Telex: 22996 UNHAB KE