Notes the high heat loss in Canadian houses due to air leakage and condensation problems caused by uncontrolled moisture movement into the exterior wall structure. Recommends the installation of an air-vapour barrier to form a completely sealed envelope around the house structure except at doors, windows, vents and other obstacles. The recommended thickness for the polyethylene sheet of the air vapour barrier is 6mm, which is continually sealed at all joints. Details the recommended installation procedures for realising an air-vapour barrier. Once a house has been provided with one of these barriers mechanical ventilation is necessary.