Abstract: A building having interior and exterior walls, the building comprising supporting members, a continuous vapor barrier and a continuous air barrier, the continuous air barrier being formed by the continuous vapor barrier with supplementary air permeable membrane portions positioned with the building when formed, the supplementary membrane portions extending between the interior and exterior walls extending between abutting supporting members disposed proximate the floor, foundation wall, and preferably the ceiling of the building when completed, the supplementary membrane portion continuously extending from under the cladding of the exterior wall to under the vapor barrier of the interior wall between the abutting supporting members, and thereby with the continuous vapor barrier providing a continuous air barrier for the building.