Pamela Howat, Senior Technical Advisor at Proctor Group, explains the similarities and differences between membrane terminology. Construction membranes have a host of applications that directly impact on building performance and the comfort of building users. As a result, a lot of terminology comes with specifying and installing membranes. Over time, the term ‘vapour control layer’ (VCL) has come to be replaced by ‘air and vapour control layer’ (AVCL). This change has been dr