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Insulation and Air Sealing

Insulation and Air SealingThe U.S. Environmental Protection Agency (EPA) estimates that proper insulating and air sealing measures can save homeowners up to 20 percent of their heating and cooling costs or up to 10 percent of their total energy costs. This section provides information on the need for insulation, types of insulating materials, ways to detect air leaks, and techniques that can be used to seal air leaks in homes.


Insulation is one of the most effective ways consumers can save energy, reduce their heating and cooling costs, and improve comfort levels in their homes. Heat flows from warmer to cooler areas, moving from the outdoors to the inside of a house during the summer months and from the heated inside spaces to unheated auxiliary spaces and the outdoors during the winter months. To maintain comfortable indoor conditions, the house’s cooling system must remove heat gained in the summer, and its heating system must replace heat lost in the winter. By providing resistance to heat flow, insulating materials reduce heat losses and gains through the building envelope, which includes the outer walls, doors, windows, ceilings, and floors.

The choice of insulating material and amount of insulation needed for a home depends on the climate, the type of building, and the characteristics of the specific building component being insulated. Other considerations include life-cycle costs and ease of installation. Commonly used insulating materials include fiberglass, mineral (rock and slag) wool, cellulose, plastic and natural fibers, foam boards, and polystyrene. These materials are available as batts, rolls, blocks, foam boards, panels, and sprayed foam. An insulating material’s ability to resist conductive heat flow is measured by its R-value. The higher the R-value, the greater the material’s insulating power.

Most insulation systems resist conductive and sometimes convective heat flow. Radiant heat gain, which increases cooling costs in hot climates, can be effectively addressed with radiant barriers and reflective insulation systems.

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Sealing gaps and openings in the building envelope is another effective way to reduce heating and cooling costs, save energy, reduce air drafts and moisture problems, and improve indoor air quality and comfort. Air sealing should be done before insulation is added because air leaks reduce the effectiveness of insulation; in addition, the presence of insulation could make some air leaks difficult to access.

Air leaks can be detected by inspecting cracks and openings, especially around window and door frames, plumbing and electrical fixtures, and ducts as well as in the attic and basement. The U.S. Department of Energy lists common locations of air leaks in homes on its website. A qualified technician can conduct a blower door test, which detects air leaks precisely and determines the home’s air infiltration rate.

Air leaks can be eliminated with simple techniques such as weatherstripping and caulking. Weatherstripping seals gaps around movable building components such as doors and windows. Commonly used weatherstripping materials include metals (such as bronze, copper, stainless steel, and aluminum), vinyl, felt, and open-cell foams.

Caulk is a flexible material that can seal small cracks and openings between stationary building components such as door and window frames. In addition to eliminating air leaks, caulking can prevent water leaks around plumbing fixtures such as water pipes, faucets, drains, and bathtubs. Caulk is usually packaged in a disposable cartridge that can be used in a half-barrel caulking gun, although it can also be packaged in aerosol cans and squeeze tubes or sold in ropes. Caulking compounds are available with varying properties, strengths, and prices.

After reducing air leaks, consumers should ensure that their home has adequate air circulation and healthy indoor air quality. (See the “Adequate Ventilation” section for more information on ventilation in homes.)

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