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close this bookCompressed Earth Blocks - Volume II. Manual of design and construction (GTZ, 1995, 148 p.)
close this folderThe project's building dispositions
View the document(introduction...)
View the documentTypes of wall
View the documentTypes of structure
View the documentFoundations and footings
View the documentOpenings
View the documentReinforcement
View the documentFloors: structures
View the documentJack arches and vaulting
View the documentRoof classification
View the documentFinishings
View the documentInstalling technical systems
View the documentCharacteristic strength of CEBS
View the documentSafety and height to width coefficients
View the documentPermissible constraints
View the documentBuilding economics

Building economics

Comparative cost analysis

A comparative cost analysis must take account of a number of factors, on several levels.

Clearly, the comparison cannot be carried out taking a single unit cost for the compressed earth block alone.

The examples considered here show that for 1 m² Of wall, the cost of the block alone is not enough.

This is because the feasibility of a compressed earth block industry and its advantages from an economic point of view depend on:

- the cost of the raw materials (quarrying, transport);

- the cost of the blocks (production);

- the costs of labour (brick-makers, builders, etc.);

- the type of production and construction organisation (self-help building, hiring skilled labour, using a building contractor);

- the type of building system used for the structures;

- the quality of finishings.

The examples we take compare 1 m² of finished wall, one in stabilized compressed earth blocks and the other in sand-cement blocks with a reinforced concrete supporting framework, and this in various contexts.

Analysis of the results clearly shows that it would be difficult and totally arbitrary to draw universally applicable conclusions. When all the factors are taken into account, a solution selected as viable in one context, may not be so in another.

Although interesting, this analysis cannot be regarded as complete if it fails to take account of the final objective, which is to build a complete building. A cost comparison of the whole process must therefore be carried out taking account of the production process of materials and the construction process of the structures in a specific socio-economic context.


FIGURE

COST BY TYPE OF ORGANIZATION

U.S. $/ m²

GUINEA BISSAU

PHILIPPINES

self-help building

3.90

2.95

hiring skilled help

4.87

5.99

building company

5.73

8.26

BREAK-DOWN FOR SKILLED HELP

TOTAL $ / m²

4.87

5.99

investment

23 %

12 %

wages

20 %

51 %

raw materials

57 %

37 %

COST BY TYPE OF ORGANI7ATION

U.S. $/ m²

GUINEA BISSAU

PHILIPPINES

self-help building

5.42

5.43

hiring skilled

6.88

10.01

help



building

10.12

18.62

company



BREAK-DOWN FOR SKILLED HELP

TOTAL $ / m²

6.88

10.01

investment

7 %

3 %

wages

21 %

46 %

raw materials

72 %

51 %

COST OF RAW MATERIALS

U.S. $ / m²

GUINEA BISSAU

PHILIPPINES

water

0.02

0.01

cement

2.74

1.86

earth

0.03

0.34

COST OF RAW MATERIALS

U.S. $ / m²

GUINEA BISSAU

PHILIPPINES

water

0.03

0.01

cement

3.14

2.13

gravel

0.12

0.59

sand

0.21

1.10

steel

0.67

0.57

paint

0,49

0.29

wood shuttering

0.30

0.42

COST BY BUILDING ELEMENT

%

GUINEA BISSAU

PHILIPPINES

CEB blocks

62 %

53 %

mortar

11 %

8 %

whitewash

5 %

11 %

masonry

22 %

28 %

COST BY BUILDING ELEMENT

%

GUINEA BISSAU

PHILIPINES

sand-cement

21 %

23 %

block



mortar

3%

2%

infill

16 %

12 %

reinforced

22 %

17 %

concrete



posts



render

20 %

29 %

paint

8 %

6 %

masonry

10 %

11 %

Fig. 179: Cost comparison of 1 m² of wan in CEBs and on sand-cement blocks, according to various factors.

COMPARATIVE ANALYSIS

Total cost comparison

(The context is a project in Senegal.)

Significant saving in the cost of the wall masonry does not necessarily translate into a saving which is as significant in the total cost of the building.

The example that we consider here illustrates that for the same type of simple house plan with various wall building systems, the house with compressed earth block walls costs 30% more than the house with adobe walls, whereas taken on its own the cost of the masonry is 73% higher.

Similarly, the compressed earth block house costs 32% less than that built with sand-cement blocks, whereas the wall masonry represents an economy of only 32%.

The difference results from the fact that the sand-cement block walls require finishing renders, the cost of which have a big impact on the total cost of the building.

The potential economy of the compressed earth block disappears altogether if a different roof is used, as shown on the lower table. One must compare like with like. If more expensive choices are made for the other elements of the building (here the roof), the advantage of having used CEBs may be lost.

On the other hand, given a similar price and quality, one can choose between a compressed earth block house to which additions can be added (public utilities, out-buildings, etc.) and a house in sandcement blocks with no additions.

In this case, there are other arguments in favour of the CEB, including:

- creating skilled jobs,
- the foreign currency economy,
- the economy of raw materials,
- better thermal comfort.

The last table illustrates/his possibility: for the same cost as the sand-cement block house, one can have a more comfortable CEB house.

Finally, it should also be mentioned that the structural and architectural design of the building has a determining effect on the total cost.


FIGURE Fig. 180: Comparison of total costs of similar buildings for a project in Senegal.