The Building Envelope
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A building envelope is the shell that separates the interior living environment of the building from the exterior environment. Building envelope components separate conditioned spaces from unconditioned spaces or basically, the building envelope separates the inside from the outside. Areas that have no heating or cooling sources are considered to be outside the building envelope. A space is conditioned if heating and/or cooling is deliberately supplied to it. If you have insulation on the floor of the attic (sitting on the attic side of the ceiling), then your attic is outside the building envelope. If your insulation is on the underside of the roof deck, then you have an unvented attic and the attic is within the building envelope.
Air leakage through the building envelope accounts for 30-40% of the energy used in buildings in the United States. Anything that can be done to minimize this energy loss will save the building owner a substantial amount of money and on a larger scale be very beneficial for the country as a whole by reducing overall energy consumption. In addition to significant heating/cooling energy loss, air leakage through the building envelope can permit moisture and condensation to collect in the walls and attic. This internal condensation creates significant problems for buildings and occupants alike. Moisture causes reduced insulation R-value, poor air quality and mold and mildew, which may lead to structural damage.
Closed Cell Sprayed Polyurethane Foam (ccSPF) addresses all of these issues. When applied in liquid form, the foam quickly expands 20 to 30 times its initial thickness, filling every crack, crevice, gap and hole in the building envelope. Areas where it is not feasible to apply SPF foam (for example: where the bottom of the wall meets the floor or around window and door framing) are either calked or canned foam is applied. The end product is an unbroken envelope separating the interior and exterior of the building except for window and door penetrations. The actual air leakage rate of closed cell foam is 0.00 +or- 0.01(L/s)/m sq. using the ASTM E-283 testing method. This is geek speak meaning closed cell foam does not let any air pass through it.
Moisture condenses in a wall or in the attic when warm moist air from the interior of the building meets the cold surface of an exterior wall. This condensation may lead to reduced efficiency of insulation materials other than ccSPF and also mold and mildew growth within the wall. Severe cases may even lead to dry rot and structural damage. Closed cell foam has a moisture vapor transmission (permeance) rate of 0.23 Perms at a 2 inch thickness using the ASTM E-96 test. This is more geek speak meaning that only a tiny amount of moisture vapor can pass through the foam. The end result of the low air leakage and vapor transmission rate is that very little interior air ever reaches a cold outside wall and if it does, there will not be enough moisture in the air to allow any condensation.
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Thermal Roof Systems, Inc. • 6750 Florin Perkins Road, Suite 400 • Sacramento, CA 95828
Phone:(916) 387-1300 • Fax: (916) 387-1302
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