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 The Envelope, Please A well-sealed house “envelope” is key to keeping heating and cooling costs minimized. Sealing a home from outside air is easy during the construction process. That's why it's important to pay close attention when the foundation is laid and the house is framed, plumbed, wired and insulated. Make sure the exterior of the foundation is covered with rigid insulation. The area where the foundation meets wood (called the sill) should be sealed with a special seal. Whenever possible, builders should avoid placing ducts and pipes in outside walls or uninsulated spaces. Ducting placed in attics or other areas that aren't heated or cooled should be insulated. All ducting seams should be sealed with mastic or a special tape designed for the purpose. Any plumbing or wiring that penetrates the envelope of the house should be sealed up tight with caulk or spray-foam insulation. When insulating, it pays to add extra insulation when possible, especially in the ceiling or attic. You can also specify that headers above doors and windows be insulated. Once the house is insulated and the inner vapor barrier and outer shield are installed, all joints and seams should be taped, caulked or foamed to create a tightly sealed envelope. With the envelope completed, have a blower door test done by the heating contractor or builder to look for air leaks in the envelope. In this test, a technician installs a blower to cover the opening to an exterior door. When the blower operates it creates a pressure differential between the inside and outside of the house equivalent to a 20 mph wind on all sides of the house. Technicians then find air leaks around the house by spraying chemical smoke at suspected leaks to see if there is air flow in the area.
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