oil, 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 metals, pollen, pesticides, particulates, and mold spores—and redistribute it throughout the home. Government sources say sealing ducts can reduce energy consumption by as much as 20% and reduce the amount of air pollutants redistributed indoors.16
In addition to sealing ductwork, DOE and many building experts now recommend sealing vented crawlspaces, especially in areas of high relative humidity.17 Homes in the U.S. Southeast historically have been built over vented crawlspaces with the idea that it is essential to circulate cooler air under the floor in summer and to allow moisture that emanates from the soil a way to disperse. However, building scientists have now determined that allowing humid outside air to enter crawlspaces can cause moisture and mold problems. “Venting crawlspaces made sense only when you had no air conditioning, no insulation, and no crawlspace walls,” says Joe Lstiburek, a professional engineer and partner at Boston-based Building Science Corporation.
Lstiburek and some other energy experts also recommend sealing vented attics—another move that would have been considered heresy just a decade ago. The rationale for venting attics has primarily been to flush the heat that radiates through the roof in summer. But by insulating the underside of the roof instead of the ceiling and closing off the gable and soffit vents at the ends of the roof and under the eaves, temperatures in the attic are reduced as less heat radiates through the roof and hot exterior air is barred from coming in the vents. “We’ve seen summer temperatures [in unvented attics] dropping from 140 to 85 degrees,” says Ed Reeves, engineering manager for insulation manufacturer Icynene Corporation. This means HVAC systems can operate more efficiently, as air leaking or radiating from the system is contained in the conditioned space, and systems are not exposed to temperature extremes.
One of the most efficient ways to insulate a roof, for both new and existing homes, is a product known as spray foam insulation. As its name implies,