In sub-Saharan Africa, timber has always been used, traditionally, for roofing (flat beams and rafters made from rough timber and branches, supporting laths covered in earth); such roofs are supported by adobe / mud walls, incorporating load-bearing timber posts.
Population growth in recent times, together with increasing desertification and regression of forested areas, means that these traditional building techniques are no longer feasible..
People in rural areas now have to resort to buying sheet metal (corrugated iron) and sawn timber beams and rafters for roof-building. These imported building materials, with their deplorable thermal, acoustic, and aesthetic properties, are often beyond the means of many people. They have to be paid for in cash, often a problem for families living outside any formal economic system. Finding the necessary funds becomes a major drain on family resources, and does nothing to promote sustainable development.