Weather-tightness – A Review of Exterior Wall Assemblies

The building industry in New Zealand is in an environment of panic over unacceptable problems with buildingenvelopes – too many are leaking. This has evolved in the past decade and has been attracting increasing mediaattention. Headlines have grown more sensational. The problem was originally described as one of damage to interiorsand wood decay. It is now described more correctly, as moisture ingress.This paper reviews exterior wall assemblies currently used in residential construction and in low rise buildings withlight framed walls (timber or steel) with NZS3604 type claddings. The climates that are involved in this review arethose of coastal New Zealand with annual average rainfall in the 1.0 to 1.5m range. The temperature and humidityrange limits the potential for problems from condensation from interior humidity. The sources of moisture areessentially external.