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MPhil in Engineering for Sustainable Development

global challenges, engineering solutions

Studying at Cambridge

Mauricia Nambatya

Investigating the Rationale for Material Selection in Tropical Housing Projects in Uganda: A Case for Interlocking Stabilised Soil Blocks (ISSB) Technology.

Behind Uganda’s housing construction industry are conventional practices in the choice of building materials, particularly burned bricks (BBs) bonded together with thick mortar of up to 30 mm to erect walls for housing. Due to the growing population, the demand for houses in Uganda has increased in the recent years, increasing the demand for building materials. However, meeting this increased demand can speed up deforestation and worsen the effects of climate change since the firing of bricks in Uganda takes 5.7 times more energy than that recorded in the ICE database of general baked clay bricks in the UK.


The use of Interlocking Stabilised Soil Blocks (ISSB) technology where cement is added to soil and compressed in a block press is an environmentally friendly and appropriate building technology alternative. The blocks are air-cured rather than fired. They are more durable with 80 % higher compressive strength than BB and even more cost-effective per square metre with up to 40 % cost savings accruing from dry stacking and less mortar for plastering and rendering. ISSB block presses are also now more available than in the past with Makiga and Hydraform Uganda as local suppliers.
Despite the ISSB benefits, the technology has not been fully integrated in urban housing. This research set out to investigate the current barriers to more widespread adoption of ISSB technology in relation to the rationale for building material selection. Such a research was intended to identify the specific areas that the promoters of sustainable tropical housing should focus on when disseminating the use of ISSBs.

Through a case study of ISSB construction operations by HYT Uganda (NGO) and Technology for Tomorrow T4T (Innovator) that involved unstructured field interviews, observations as well as documentary evidence, this research provided a holistic view into the problem of slow adoption of ISSBs as industry continues to use BBs and the findings were analysed by triangulation.

The study found that cost, durability, availability and acceptability by clients were the common reasons for material choice. However acceptability by clients was governed by their perceptions towards stabilised soil. From the field interviews, it was established that social attitudes point to stabilised soil as an inferior technology meant for rural settings while adding cement to soil is viewed as wastage. Hence the technology is perceived expensive and unaffordable.

The study concluded that, it is crucial for promoters to understand the local perception towards the ISSB technology and should therefore focus on educating clients as a first step. Client understanding of the ISSB technology as a sustainable and cost effective technology for building construction will go a long way in the adoption of this technology.

The implications for further research include (i) How ISSB promoters can best communicate ISSB technology to clients and (ii) The role of policy, legislation and government in promoting environmentally friendly building materials in Uganda.

Key words: Material selection, Tropical housing, Sustainability, Climate Change, ISSBs