Abstract: A building construction has an outer wall adjacently positioned to a plurality of vertical, transversely spaced parallel studs, each stud having a first side substantially parallel to and in adjacent proximity to the outer wall. The stud sides are substantially coplanar and each stud has a second side spaced inwardly from the wall, with the second sides being substantially coplanar. Insulating spaces are defined between adjacent studs and the planes of the first and second sides. A first plastic sheet which is substantially coextensive with the area defined by said first sides is adjacently supported to said first sides. A plurality of elongated plastic bags, each insertable between adjacent studs and each bag volumetrically expandable to substantially displace the space between adjacent studs, have elongated webs connecting adjacent bags with the webs being substantially coextensive with the second sides and contiguous therewith.