The Thermal Envelope
Floor, wall, and roof areas that adjoin unheated spaces make up the thermal envelope (TE) of a house. Building the house with an air-tight TE is one of the most difficult PH requirements to achieve. Maintaining air barrier continuity at transition points in the TE is critical. I began by wrapping the concrete slab foundation with a reinforced plastic sheet, which was installed with great care to eliminate possible holes. The plastic was cut to lap the plywood wall sheathing and plywood subfloor (by the old foundation) by 3-4 inches. These joints were taped with a high quality construction tape to provide a durable and air-tight connection. The same tape was used to seal all joints and intersections of the plywood subfloor, exterior wall sheathing, and underside of the roof trusses (where plywood was installed to help guarantee the continuity of the air-tight TE). The intersection of the subfloor and wall sheathing could not be taped, so this intersection was sealed with EPDM gaskets. Finally, the windows and doors were installed, using the same tape to seal them to the framing.