This report by UKCMB Technical Director Dr Valentina Marincioni, and UKCMB affiliates Bingyu Xu and Toby Cambray presents the existing evidence on the functionality, performance, longevity and failure modes of air and vapour control layer (AVCL) membranes in relation to moisture movement in traditional building construction. The methodology involves a comprehensive analysis of peer-reviewed literature from databases such as Web of Science and Scopus. An initial general review, using keywords, establishes the concept and theory of AVCLs. The study then explores and summarises AVCL definitions, current products and their properties. Finally, it presents evidence on AVCL performance in building systems, focusing on internal wall insulation, timber-frame walls, insulated roofs and suspended floors, using both in situ measurements and hygrothermal simulations. The findings indicate that while there is some evidence on the benefits and limitations of AVCLs, further research is required to fully understand them and the impact they have on the performance of building fabric systems particularly in buildings of traditional construction.
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