The focus of sustainability in the building sector is gradually shifting towards the environmental impact of building design. A substantial amount of research has already been performed on the assessment of the environmental impact and numerous impact assessment tools have been developed. However, as the architect is usually the key actor in the design process, the assessment of the environmental impact should be adapted to his work method. Up to now, few research concerning the architect’s practice and knowledge regarding sustainable material use and the environmental impact of building design has been performed. Therefore, a survey on sustainable material use was conducted in February 2014 among 364 Flemish architects. From this survey it appeared that sustainable material use is not frequently applied in practice and architect’s knowledge is rather limited. So there is a clear need to sensitize the architects regarding the importance of the environmental impact of building materials.