Most new buildings of any size require a frame to stabilise the walls and deal with earthquake resistance and wind loading. Brickwork or blockwork buildings therefore require piers at regular centres (generally around three meters) that link to a foundation and a ring beam at eaves level. Piers can be made by increasing the area if brickwork or bricks can be spaced out to act as permanent shuttering for a reinforced concrete column.
Concrete is not generally recommended as a wall infill due to the high cement content in concrete blocks, mortar and the cement render required to finish the wall. East Africa's proverbial red earth provides enormous low carbon alternatives to concrete, which may be as simple as mud mixed with straw to make cob, or soil stabilised with lime or cement. Earth construction is more efficient with pre-formed mudbricks, compressed earth blocks, earthbags or fired clay bricks.
Fired Clay Bricks
Large clay reserves have made fired clay bricks the preferred construction material in East Africa. Take care to ensure bricks are manufactured sustainably
Local handmade bricks are sundried and fired in firewood-hungry roadside kilns in an inefficient process that is contributing to widespread deforestation in the region. An alternative manufacturing process utilises waste materials such as cassava peel or coffee husks as the primary energy source for firing bricks. This process is undertaken in small-scale industrial brickwork factories, with the added benefit that factory-made bricks use less cement mortar and can be laid to a fair-faced finish so they don't require an external coat of cement-based render.
Lake Bunyonyi Secondary Bricks were moulded from good quality clay and sundried before being stacked up into giant furnaces.
Earth can be strengthened using a 5-10% cement or lime stabiliser and compacted into earthbags or rammed earth walls.
In order to be suitable for stabilised earth construction, soil must have a low clay content of less than 15%, although soil with higher clay content can be supplemented with additional sand. Low-density stabilised earth will be porous and weak so the stabilised mix must be manually or mechanically compacted. The 'rammed earth' technique uses powered tampers to compact the semi-dry soil mix is packed into degradable sacks, which are laid end to end and manually tamped into earthbag courses. A loop of barbed wire is laid between courses to act as mortar. Unlike rammed earth, earthbags require additional plastering with cement or lime render.
Fresh rammed earth wall produced by Hive Earth - a specialist earth construction company based in Ghana.
Stabilised earth can be compressed into dimensionally stable building blocks for easy and efficient construction.
Compressed stabilised earth blocks (CSEB) are comprised of stabilised soil mix compressed by diesel or man-powered machines into solid building blocks. CSEB are strong and dimensionally stable but like fired bricks require a 12mm cement mortar joint to hold them together. Interlocking stabilised Soil Blocks (ISSB) are compressed into a stepped profile, which allows them to interlock vertically and horizontally to their adjacent unit eliminating the requirement for cement mortar. ISSB are an extremely sustainable option, but the block shape limits design flexibility and buildings can suffer architecturally from an unresolved corner solution.
Mzuzu Health Centre Phase 1 uses a mechanical hydraform press to produce interlocking stabilised soil blocks
Wattle and Daub
This traditional material could be revived providing the underlying structure is sourced from a sustainably managed timber plantation.
Wattle and daub is an ancient construction method, where a well braced timber frame with small scale timber laths, know as the wattle, is daubed with a sticky soil mix containing clay, sand, animal dung and straw. Wattle and daub walls are well insulated die to the high straw content but they lack the thermal capacity of solid masonry walls. Daub render can be strengthened with the addition of lime or cement or the wall can be whitewashed to increase resistance to rain. As long as the underlying structure is responsibly sourced, wattle and daub is a cheap and low-impact sustainable building option.
Living Tebogo by Base Habitat adapts vernacular wattle and daub construction (left) to produce a unique finish (right).
Stone construction is relatively uncommon but where local stone is available it can be a sustainable option for wall structure or cladding.
East Africa has an impressive variety of stone - from sandstones, quartzites and granites to the remarkable Karamoja marble. The predicament surrounding stone as a construction material on a larger scale is the absence of professional mining infrastructure and industrialised mass production. This is largely reducing the use of stone to cladding or for external works. However, once a certain roughness is accepted, locally sourced stone can be used structurally without having to deploy heavy machinery.
Ruhehe Primary Volcanic rock is built around a central core of steel and concrete to guarantee stability