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close this bookThe Basic of Biomass Roofing (GTZ - ITDG - SKAT - CRATerre-EAG, 1997, 36 p.)
View the document(introduction...)
View the documentIntroduction
View the documentGrass thatch
View the documentPalm thatch
View the documentWood tiles (shingles and shakes)
View the documentRoof sheets with organic fibres
View the documentTreatment of biomass materials: preservation
View the documentFire protection
View the documentSources of further information
View the documentKey questions
View the documentRecommendations
View the documentBASIN
View the documentBack cover

Palm thatch

Fundamental information

Palm leaves are widely used because they are so plentiful and because they are innately suitable for roofing. They are simple to process and easy to fix to a roof structure. However, even the most durable palm thatching will rarely last more than 7 years, whilst traditional techniques often need annual repair. They are excellent for temporary structures, but for housing, people tend to change to corrugated iron or other materials as soon as they can afford it.

The leaves are used for roofing either in their natural form, as they are cut from the tree, or alternatively, the leaf blades are made up into mats. There are several ways of making these mats. In East Africa the mats are called makuti. In many Far East countries they are known as atap.

Basic techniques for processing and use

Materials

Palm leaves must be mature and dry before they are used for thatch. Each species has its own growth cycle which may vary according to soil conditions and climate, but with most, the leaves take a year to mature. For thatching purposes leaves are classified by the way that the leaf blades are attached to the stem. There are two types.

Coconut (cocos nucifera) leaves are the most widely available thatching material in the humid tropics. Hundreds of millions of people rely on them. An average tree produces up to 40 leaves every year. The leaf comprises up to 200 leaf blades which grow, at an angle, to the leaf stem.

Feather shaped leaves have leaf blades which hang, usually at an angle, on both sides of a straight stem. Fan-shaped leaves have blades that radiate from a woody, fibrous core. Doum palm, which is often used in drier parts of Africa has fan shaped leaves.


Nipa palm thatch in the Philippines

Many other palms produce fan shaped leaves. Nipa, which grows in marshy land is primarily cultivated for its leaves which are mostly used for thatch. They last better than coconut leaves, but can't compete with sheet or tile roofing for modern housing.

Processing

There are two ways of preparing feather type leaves to make thatch mats.

In the first method the leaf blades are stripped from the stem and then stitched to a thin wood batten. This batten may be made from the palm leaf rib, or perhaps from split bamboo. The principle for making the most durable mats is to make sure that the leaf blades are squeezed tightly and neatly together as they are stitched onto the batten. The standard mat of 600mm length should be made of about 200 leaf blades. In East Africa this technique is called makuti. In Far East countries a similar technique know as atap is used.

The second method is to split the stem in two so the leaf blades hang from one side. The two pieces are laid back to back and the leaf blades woven together to form a mat. This technique, which is commonly practised in south India, is not as durable as the first as the rapid discharge of rainwater is impeded by the weaving pattern. But it is quicker to make the woven mats and, as they are longer than the other type, thatching work can be done faster.

Fan-shaped leaves generally need no preparation other than drying and flattening. They are tied, nailed or wedged into place on a roof with the leaf blades facing downwards.


Makuti type palm thatch mat - the complete mat is 600mm long x 500mm wide.


Woven coconut palm thatch mat

Roof structures

A steep pitch of at least 45° is essential. The structure, which may most economically be made with timber or bamboo poles rather than sawn timber, needs to be strong enough to support up to 20kg/m2 of thatch. Horizontal battens are not needed for feather-type mats; the rafters need to be set about 500mm apart for mats that are 600mm long. As with all roofing, it is advisable to fix a batten of approximately 60mm thickness along the length of the eave. This provides essential support for the first layer of thatch. A bamboo pole of this diameter will serve the same purpose.

For fan-type leaves horizontal battens are needed, usually at 150mm centres.

Roofing work

The process of laying feather type mats resembles tiling. Mats are tied to the rafters in overlapping layers starting at the eave. The thickness of the coat, and therefore the durability of the roof depends on the size of the overlap. There should be a maximum of 100mm between the mats; if sufficient material is available this gap should be reduced to 60mm.

It is sometimes suggested that palm thatch requires side lap as well as vertical overlap, but this should be unnecessary with well made mats. In fact, this may be a positive disadvantage as the extra thickness created by each side-lap creates ridges in the surface which will lead to the formation of gulleys and more rapid decay.

Woven coconut palm mats are generally laid double thick, layer by layer, to achieve acceptable durability. When the upper layer decays, usually within two years, the roof is rethatched. The decayed upper layer is discarded and the lower layer then forms the new upper layer.

Hip and gable edges and the ridges of palm thatched roofs are particularly vulnerable to wind and rain damage. Hip edges can best be protected with a metal cap. Gables should either be strengthened with additional lashing, or preferably set within parapet gables with a suitable flashing. The ridge cap is vital to ensure that rain doesn't penetrate into the body of the thatch. The simplest technique is a metal sheet saddle, but any watertight material, such as ferro-cement should be effective, provided it is well secured.


Inside view of fan-shaped palm thatch


Inside view of coconut palm thatch, in the Philippines


Layering of woven palm thatch. Closer spacing produces a longer lasting thatch


Peru palm thatch


in Indonesia this type of palm thatch is up to 200mm thick

Cost and economy

The following data applies for makuti type palm thatching. With woven palm mats and fan shaped palm leaves quantities will be similar, but durability will also be considerably less.

Materials

For a feather-type palm roof with a slope of 50° and vertical lap between the mats of 60mm, 1m2 of roof surface would use 25 pieces of 600mm-long mats. An average sized house would use approx. 2,500 mats, plus string or fibre for tying and suitable material for ridging.

Labour

Preparation of mats. This work is traditionally done by women as a 'cottage industry' so the production rate is very variable, up to 40 mats per day.

Roofing work

A skilled thatcher, with one assistant would expect to lay up to 500 mats per day. Seven working days, including ridging and tidying the site is sufficient for an average sized house.

Durability

A steep roof with a thick thatch is more durable than a thin, shallow pitched roof. The higher cost of a steeper, thicker roof is more than offset by the increased life, but choice is always a trade-off between cost and performance. The maximum economic life of a palm thatch, using the best available materials and a skilled thatcher is 10 years.

Further Information

Trelaun B.; Tuiles de Bois - USA and Canada; GRET, Paris, 1984.

Powter A.; Papua New Guinea Shingle and Shake Manual; Forest Products Research Centre, PNG, 1976

Checklist of benefits and problems

Potentials

Limits



· Palm leaves are widely available and usually inexpensive, especially in the humid tropics.

· Thatch is combustible, and inordinately expensive to make completely fire proof with chemicals. Insurance may not be available or the premiums may be very costly.

· Harvesting, processing and thatching work is labour intensive.

· Combustibility and limited life span restricts use to building owners who have ready access to labour and materials.

· Skills are widely known where palm leaves are available, and are easily learnt.

· Harvesting and processing has not been mechanised, so inexpensive labour is essential.

· Repair and maintenance is straightforward.

· The edges - hips, gables and ridges of palm thatched roofs are very vulnerable to wind damage, unless protected by a metal sheet capping.

· Palm thatch is light in weight, so roof timbering need not be very expensive.

· Traditional methods are often very short lived so people may be reluctant to invest in more expensive palm thatch.

· Their thermal insulation value is high, so palm leaf roofs are comfortable in warm climates.

· Traditional palm thatch is associated with temporary structures and previous generations, thus not perceived to be 'modern'.

· This type of roof looks attractive, it blends well with the natural environment and, being a renewable material, is ecologically sound.

· Combustibility means that urban use is not recommended. And in regions prone to civil conflict this is a major drawback.

· Lightweight roofing is less dangerous in earthquake zones than monolithic, heavy roofing.

· Relatively low initial cost may be a false economy compared to more durable and less combustible coverings.

· Though easily damaged in high winds, they are easy to repair or replace.