ls, 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, spray foam is sprayed from a gun and readily sticks to most surfaces, expanding to provide a highly effective seal. Reeves says medium-density spray foam has a higher R-value (i.e., insulating value) per inch than fiberglass or cellulose. But of course, Katz says, as with everything else, spray foams can be (and sometimes are) poorly installed and therefore don’t always perform as advertised.
Spray foam does have its disadvantages. It can cost more than four times as much as fiberglass or cellulose, installed, and it can be a nuisance to install. Michael Chandler of North Carolina–based Chandler Design-Build describes what can happen if proper precautions are not taken: “As the foam is sprayed, small droplets of foam end up in the air. This stuff gets in your hair, in your skin, and on your clothes.”
Moreover, although there are no published reports of health effects resulting directly from spray foam, the product does contain isocyanates, and unprotected exposure to this class of chemicals may cause asthma, lung damage, respiratory difficulties, and eye and skin irritation.18 Spray foams also contain flame retardants, most commonly tris(1-chloro-2-propyl) phosphate, a mild skin and eye irritant.19
Professional installers wear personal protective equipment to prevent exposure to foam droplets, Reeves says. But Chandler says that is not always true of workers who come in after the spray foam has dried to shave it down to a flat surface. Despite industry recommendations, “the people doing the shaving often don’t even wear a dust mask,” Chandler says.
Toward Better Retrofits
To ensure energy-efficiency retrofits provide a net benefit for occupants, the DOE is developing a set of voluntary guidelines for workers involved with weatherization assistance and home energy upgrade program activities.20 The guidelines will outline steps and specifications to ensure various types of retrofit jobs are conducted properly as well as essential skills contractors must have to perform the work. The guidelines are expected to help