Global demand for all energy sources is forecasted to grow by 57 percent. U.S. demand for energy is forecasted to increase by 31 percent and the demand for electricity in the U.S. will grow by at least 40 percent.
This trend, along with the groundswell of the green building industry is creating a need for more efficient and cost effective systems to address energy performance issues in new and existing buildings and homes.
Air infiltration can account for 30 percent or more of a home’s heating and cooling costs, and contribute to problems with moisture, noise, dust and the entry of pollutants, insects, and rodents. Reducing infiltration can significantly cut annual heating and cooling costs, improve building durability and create a healthier indoor environment. According to a 2005 National Institute of Science and Technology (NIST) study, an energy savings of up to 62 percent can be realized by undertaking specific air tightness measures. In addition to energy loss, air infiltration reduces occupant comfort, interferes with efficient operation of mechanical systems, reduces indoor air quality and contributes to condensation and moisture damage in the building envelope system. Using tight construction methods is said to be like closing a hole in your wall the size of an open window.
According to the Air Barrier Association of America, a “typical 2,500 square foot home has more than a half mile of cracks and crevices.” Unsealed, about a third of the air leakage in a home occurs through the floors, walls, and ceilings.
The biggest contributors to air infiltration are usually hidden from view and connect the house to the attic, the crawlspace or basement, although windows, doors and outside walls are also notorious for air leakage.
Many common leakage sites include dropped ceilings, kitchen soffits, duct and plumbing chases, attic accesses, pull down stairs, recessed light fixtures, mechanical room closets, and wiring penetrations. A
large source of air leakage can come from key framing junctures, such as attic-to-knee wall transitions. In the floor, you can find major leakage sites, such as the tub drain, plumbing, and HVAC and electrical penetrations. In the walls, the band joists (for two story homes), window and door rough openings, and penetrations through the drywall and exterior sheathing are primary leakage sites.
One common misconception is that fibrous insulation will take the place of, or serve as an air barrier. Fibrous insulation, including fiberglass and cellulose does not stop air leakage! Fiberized insulations will only properly insulate a cavity if it is, in turn, properly air sealed. Air movement within fibrous insulation can contribute to up to a 30 percent loss of printed R-value. In older homes, dirty fiberglass is a telltale sign of air movement (it simply collects dirt like a filter). Certain types of insulation, such as Open cell
foam (1/2 lb. foam), and Closed Cell foam (2 lb. foam) can be extremely effective at reducing air flow as well as heat flow.
Consumer demand for efficiency coupled with the increases in building energy-code requirements, are causing homeowners, builders and community developers to more frequently turn to open and closed
cell foams as an insulation and exterior material. The materials have a higher “true” R-Value per inch than competing products, significantly reduce air and moisture infiltration into the building envelope and provide continuous coverage, thus providing labeled R-Value without settling and without R-Value degradation after installation, which is a significant problem with other insulation materials.
There are tools that can be used to test the air tightness of a home or building. One of the most effective ways to test air tightness is the use of a special fan called a blower door. Often, energy efficiency incentive programs such as the DOE/EPA Energy Star program require a blower door test to
confirm the air tightness of a home or building. It is recommended that you have a professional energy efficiency rater perform this test. Another tool that can be used in conjunction with a blower door or alone is an infrared or thermal imaging camera. Infrared thermography cameras produce images of
invisible infrared or "heat" radiation and provide precise non-contact temperature measurement capabilities. When used in combination with a blower door assembly, infrared cameras will highlight areas of air leakage in a home or building’s exterior envelope. Contact your local energy efficiency rater professional and/or local insulation professional to uncover and repair air leakage problems.
Below is a list of air sealing materials that can be used, in combination, to create a tightly constructed home or building.
- Caulk: Seals gaps of less than ½”. Be sure to select the correct grade of caulk based on theapplication area.
- Spray Foam: Otherwise known as “two component foam.” Fills large cracks and small holes. Extremely effective as an air barrier. It is recommended to have a professional contractor install spray foam insulation.
- Can Foam: Otherwise known as “one component foam.” Fills medium cracks and small holes. Can be bought at most construction supply stores.
- Backer Rod: Closed cell foam or rope caulk. Can be pressed into a crack or gap with a putty knife. This is often used around window and door openings.
- Gaskets: Apply under the bottom plate before an exterior wall is raised.
- House Wrap: Install over exterior sheathing. Must be sealed with house wrap tape or caulk to form an airtight seal. This will resist water, but is not a vapor barrier.
To be continued...
For more information on air sealing practices or techniques, you can go to the following websites: