School buildings in developing countries
Practical Action
Walls
Stone - rough hewn (rubble) or worked smooth (ashlar) blocks; the former being cheaper
to produce while much less mortar is needed with the latter if they are well-finished
Stabilised soil blocks - now a proven low cost technology, especially in areas where soil of
low shrinkage - which requires less use of costly stabiliser, is available locally
Rammed earth or pisé - a low cost material, though stabiliser might need to be added to
control cracking, but labour-intensive and heavy to work with. The earth wall is built up
between shutters or formwork, progressively moved up the wall as construction proceeds.
Use of internal and external plastering is preferred with rammed earth buildings to reduce
the need for maintenance, which is otherwise high, and the harbouring of insects and
other pests.
Fired clay bricks - require a higher level of skill for laying than the larger blocks; also in
some cases field bricks might be warped and of variable size, so relatively large quantities
of mortar are required
Concrete blocks - usually hollow rather than completely solid blocks are used as this
allows some saving on the material for the blockmaker with the same level of structural
stability as solid blocks. Blocks can be used structural or loadbearing, or used for infill.
The strength and durability requirements of blocks for structural use need to be
considerably higher than those for infill
Precast concrete panels - panels are inserted within a structural frame and bolted with
each other and the frame. Panels contain steel reinforcement, which increases the cost.
However costs can be reduced by mass fabrication, so the application of pre-fabrication
would be likely to be most relevant to very large building programmes with many identical
or modular constructions. Prefabricated components do not require high levels of skill to
erect, and erection can be relatively fast so having a low labour requirement - rarely a
priority in many developing countries.
Ferrocement - generally made by covering a steel wire-based mesh or framework on either
side with cement mortar. Costs are saved by using chicken wire rather than more
conventional steel reinforcement, and the walls of low rise buildings can be quite thin -
only a few centimetres across. Ferrocement buildings also require labour-intensive
construction, and the construction techniques are not difficult to learn. However, many
do not like the appearance of ferrocement buildings and they certainly look quite
different from conventional constructions. They also heat up and cool down quickly with
changing temperature, and there are some doubts about their long-term durability in
places where severe climate can be experienced.
Timber and bamboo - can be used where this is plentiful supply. Strong bamboo species
are a particularly versatile low cost construction material. However, bamboo and many
timber species decay relatively quickly in the climates where they are found unless they
are treated with preservatives, and there are no completely safe preservatives, though
some are less hazardous than others. Also, some preservatives have limited effect on
termites and other wood-boring insects, against which special and more costly
precautions need to be taken.
Roofs
Note that the options for good roof construction materials are generally more limited than for
wall construction materials, and the materials that offer better performance are generally
higher in cost.
Grass, reed or palm leaf thatch - a low cost option in rural areas, though it needs to be
noted that good thatching material is getting in short supply in some places. However,
despite its low cost, thatch is generally an inferior roofing material as it can harbour
insects and other pests, can be a fire risk, needs to be made up skilfully to offer
reasonable performance, and deteriorates rapidly in a tropical climate due to the effects
of weather and insect attack. If the roof needs to be renewed every few years than a
thatch can prove to be a false economy, despite its low initial cost, compared to other
roofing materials. A reasonable ceiling below the thatch roof can significantly improve
safety and the learning environment, but would add to the cost.
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