The rapid population growth in Africa calls for an enormous increase in buildings both in urban and rural areas. This will dramatically increase the carbon emissions in Africa, particularly when not specific considerations are made with regard to the high level of informality in many urban African settlements and in the overall construction sector. After elaborating on the high climate impact of the informal African construction sector, the authors discuss some major differences and how structures and quarters would need to be designed to become sustainable, and materials concepts are presented that are sustainable even in a rapid urban growth situation as foreseeable in Africa, where whole city quarters will change their surface appearance inevitably within short cycles. A prediction for the example of Kenya is made on how much CO2 emissions can be reduced until 2050, when informal businesses are included or excluded in policies and technology developments for low carbon construction. The conclusions for longevity of urban settlements are that flexible and modular structures are better than efficiency optimised buildings, and that there is no alternative to multi-storey buildings, which, however, have to stay limited in height to avoid wasteful materials use. The vertical growth is also required to create social spaces, which are important for quarters to be safe from gentrification. Materials should be ideally fully reusable or renewable, hence, structural elements are best build from cementitious materials in a modular column, girder, slab system.