The 2012 International Energy Conservation Code (IECC) includes more stringent requirements for everything from insulation to windows to lighting to HVAC systems. Jurisdictions that adopt it will also be putting more scrutiny on the air tightness of new homes and, for the first time, requiring that air tightness be tested.
The rationale is that while new homes are tighter than ever, they still leak a lot of air. Estimates are that drafty walls and ceilings account for half the heat loss in some homes. Steve Easley, a San Francisco-area consultant who works with builders nationwide on energy and building science issues, estimates that the gaps and cracks in a typical home equal a small window being open all year long. This can add significantly to energy costs, he says.
But these leaks do more than raise heating bills. “In my field investigations I find that, next to water leakage, air leakage is the biggest cause of moisture-related issues,” Easley says. “In warm climates, humid air leaking into the house can condense on cold surfaces, encouraging mold growth. In cold climates, air exfiltrating from the house can dampen the inner surface of the exterior sheathing, causing deterioration and mold there.”
The 2009 IECC started to address these problems by setting a maximum air leakage of seven air changes per hour (ach) with a 50 Pascal air pressure difference between the inside and outside of the house. (Fifty Pascals, or 50p, is roughly what you get with a 20 mph wind blowing across the house.) The 2012 version lowers maximum leakage to 1 ach for zones 1 and 2 (most of Florida, the Gulf coast, and southern Arizona), and 3 ach everywhere else. It also requires that this be certified: In the 2009 energy code, builders had the option of building to an air-sealing checklist or doing an actual air leakage test, while the 2012 version requires both.
How does a builder measure the amount of unwanted air leaking into or out of a home? The most accurate tool is the blower-door test. But while most builders have probably heard of the test—it has been around since 1970s—few are taking advantage of it.
“There’s still a big disconnect,” says Jonathan Coulter, a building science consultant at Advanced Energy in Raleigh, N.C., who trains builders on how to use the tool. “For instance, they don’t understand that the blower door can show them what the framing contractor is doing that will contribute to air leakage.”
The blower door consists of a large fan mounted in a frame that fits into an exterior door opening. The test is typically performed after the drywall has been hung and taped. Before the test can begin, all exterior windows and doors, as well as exhaust fans and flue dampers, are closed. All interior doors are opened. The fan sucks air out of the house until an onboard pressure sensor reaches the required 50p pressure difference between inside and outside. This vacuum will pull air in through cracks and gaps in the building envelope. By measuring the amount of air flowing through the fan at this pressure, an onboard computer determines the actual amount of leakage in the house. The test takes about two minutes to run.
Wind can skew the test results, but according to Coulter, there are procedures that allow the tester to compensate. In the case of gusts, that might mean taking a number of consecutive readings, while a steady wind might force testers to place the blower door in different openings. Such cases take a knowledgeable tester to accurately interpret the results. “Experienced people will get a feel for what’s an accurate reading,” Coulter says.
The blower door can do more than help the builder meet code. Even with a passing score, smart builders will use the test as a chance to determine exactly where those leaks are, so they can do better next time.
The 50p vacuum is more than a typical home would have under normal conditions, which means that air is pulled in through cracks and gaps at a greater velocity than normal. This makes it possible to go around the house and find leaks using a smoke pencil—a handheld tool that creates puffs of non-toxic chemical “smoke”—or simply by using one’s hands to feel for drafts. Most leakage tends to occur around windows, doors, ceiling lights, receptacles, and fireplaces, as well as along wall bottom plates. Easley says many builders are really surprised to learn how leaky their homes are, and where those leaks are coming from.
Builders who really want to improve their score might consider doing an initial blower door test after the home has been dried in but before the walls are insulated. This is usually done when just the ceiling drywall has been installed, unless the home has an unvented attic. Advanced Energy publishes field installation materials showing the most common problem areas, including the framing around tubs, showers, fireplaces, kneewalls in bonus rooms, and where the ceiling drywall meets the wall’s top plates.
A few remodelers have even been known to use the blower door. “If someone has a comfort complaint, the contractor can use a blower door to determine where the house is drafty and where it needs to be sealed,” says Coulter. “Tests can be run before and after the job to make sure it was done right.”
A blower door costs $3,000 to $4,000, a price tag that low-volume builders might balk at, particularly if they’re building affordable homes. The Residential Energy Services Network (www.resnet.us) and the Building Performance Institute (www.bpi.org) have lists of certified testers, with costs starting around $200 per test.
Builders who have to get the test done may want to schedule it well ahead of time. Builder magazine in early May mentioned a severe shortage of testers in at least one state, a problem that is likely to be the case elsewhere.
