After retiring from academic life, I became a member of the management committee, and then President, of the French-Burkinabé NGO, the Association 'La Voute Nubienne' (AVN), promoting the development of a market for earth-constructed timberless vaulted buildings in the Sahel. The AVN's program 'Earth Roofs in the Sahel' has seen exponential growth in the last ten years in the number of vaulted buildings constructed, and the numbers of masons trained (214 by 2011), and has spread from Burkina Faso to Mali, Senegal, Togo, Ivory Coast, and Zambia. The program's focus is on sustainable, healthy and comfortable homes for poorer rural communities, as a viable environmental and economic alternative to the expensive and unhealthy tin-roof shacks in which many African families live. In 2007, AVN received a Tech Museum Award for economic development; in 2006, one of three winners of Ashoka Changemakers competition on Affordable Housing; in 2009, one of 11 finalists for the World Habitat Award, and one of 25 laureates in the World Bank Development Marketplace Competition on Adaptation to Climate Change, 2009. . The carbon footprint of VN buildings by ERM (www.erm.com ), shows that the average VN house (25 M2), over a lifetime of 50 years, represents a saving of 2 tonnes of CO2e as compared to the current alternatives (tin roofs, timber beams, conccrete block walls). Since 2000, VN masons have built over 1300 vaults, representing a carbon savings of ~2,600 tonnes of CO2e.