ctually reduces energy consumption is relatively easy in new construction; it is more difficult in an existing building because sources of air infiltration may be difficult to find and access. Measures such as adding storm windows and weatherstripping doors may improve comfort, but experts say they have a minimal effect on energy bills. “Air escapes from the top of a building, not the sides,” says Arnie Katz, senior building science consultant with Advanced Energy Corporation, a North Carolina–based energy-efficiency services firm. “If you just tighten the sides, all you are doing is creating a more efficient cylinder.”
Katz says the first priority in tightening a building should be to seal leaks in the top; the second priority is sealing the bottom. Air, he explains, typically leaks from the home through gaps around wiring, plumbing, ceiling lights, vents, and fans.
These gaps are often difficult to access, and workers trying to reach them may find themselves facedown in fiberglass insulation, so it is important they wear proper clothing and face masks when doing this work. The Occupational Safety and Health Administration (OSHA) advises that fibers freed from insulation can cause, skin, eye, and respiratory irritation, and requires that employers provide workers with proper respiratory protection when they are blowing fiberglass insulation into an attic.12
Assuming one can actually seal these leaks, the other challenge in tightening homes is to do so without compromising the occupants’ health. This is especially a concern for buildings with indoor combustion appliances such as oil, gas, or propane furnaces and water heaters, which can produce CO. Katz warns, “Anything you do to make a home tighter has the potential for causing backdrafting13 of these appliances, because you are changing the air pressure relationships inside the house. That’s why it’s so important to hire someone who knows what they’re doing.”
Trapping of radon is another potential result of overtightening a home. This radioactive gas found in soil, rock, and water can enter the home through dirt crawlspaces and cracks in basement floors and foundations.14 Long-term exposure to radon is estimated to cause approximately 20,000 cancer deaths per year.14 Homeowners can easily test for radon with a simple kit that can be purchased at home-improvement stores for about $10–15. If detected, radon usually can be vented to the outdoors by installing vent pipes in the crawlspace or basement.
Moisture from outside air, showers, cooking, plumbing leaks, and human activity is another variable that must be dealt with when weatherizing a home. Tightening a house can close off avenues where moisture previously escaped, so it is important to identify how and where moisture is generated and how it can be controlled. Some moisture in the air is desirable, but as with ventilation, a balance must be struck, because over time, excessive moisture can contribute to asthma and allergies and can increase the presence of mold, dust mites, and vermin.15
Getting It Right
Moisture generated in bathrooms and kitchens can be addressed by adding or upgrading fan systems. ASHRAE recommends fans for kitchens and baths that circulate a minimum of 50 cubic feet per minute (cfm). However, Katz cautions the manufacturer’s rating on a fan may not be what you get when it is installed in a home. “The rating is based on a fan sitting on a table and attached to a straight ten-foot run of duct,” he says. “In a house, the fan may be connected to thirty feet of duct that turns at a right angle before exiting outdoors.” In that case, he says, you would need a fan rated at 70 cfm to achieve a 50-cfm result—a judgment that can be made by an experienced builder.
Sealing ductwork is widely considered one of the best ways to not only save energy but also improve indoor air quality. When the blower in an air handler is activated, it creates negative air pressure in the return air ducts. Leaky duct systems that pass through unsealed crawlspaces and attics suck in outside air—which may include dustborne meta