According to building scientist Justin Wilson, founder and principal of consulting firm Building Performance Solutions of Denver, you can’t even stop there. Local climate and site conditions come into play, too—average temperature and humidity, sun exposure, wind, rainfall, whether the dominant environment requires heating or cooling, and how water will be removed from the site, especially when it rains. “Builders should be a little more analytical so they put the pieces together properly,” Wilson says. “Everything affects everything else.”
WRAP IT UP In cases involving the desert, energy savings is top of mind. In its battle for progress against the elements, Las Vegas-based Sun-West Homes recently has adopted a new DuPont breathable membrane product called AtticWrap, which, when installed over rafters and trusses, seals an attic. Simply put, if you prevent outside air from coming in, you save energy. So Sun-West decided to develop a test house. Quickly, an unexpected benefit emerged from its pilot house project: improved indoor air quality.
The reason? As normal roof ventilation allows outside air into attics, it does more than drain energy efficiency. Water vapor in the air absorbs into the wood beneath the tarpaper sheathing, condenses, and eventually, leads to mold and mildew. Roof leaks create the same problems and can rot insulation over time.
With AtticWrap, “moisture escapes through micropores in the membrane to the outside instead of letting moisture in from the outside air,” says Arturo Horta, product manager at DuPont. “It gets rid of moisture and protects insulation and wood.” AtticWrap also resists liquid water. Horta says, “It’s like a tent. It sends water straight to the gutter or soffit.”
Since mold has become a major issue in Las Vegas, the opportunity to prevent it—and the inferior IAQ that it breeds—was a huge benefit to Carl Martinez, Sun-West vice president of construction; one that justifies any increased costs.
According to Martinez, wrapping Sun-West’s test house attic with the product cost $7,000 more than traditional sheathing methods, and took an extra day-and-a-half to install. He expects the extra cost to drop to $5,000 and the extra installation time to level off at perhaps one added work day.
Still, that’s a lot less than the possible alternative: “AtticWrap prevents mold and reduces the need for mold remediation, which is very expensive. We’ll be installing it in about 20 to 25 homes this year,” Martinez says.
LIKE A ROCK Roofs are not the only place to watch when it comes to structures prone to moisture and its ill effects on indoor air. Chris Ellis and Gene Baker, co-presidents of Scottsdale, Ariz.-based Hallcraft Homes, constantly are on the lookout for ways to keep their homes dry. “Any wet area in a home is a concern,” Ellis says. “We want to prevent any water-related problems, such as humidity, mold and mildew.”
A chronic sore spot: wallboard. Ordinary paper-clad gypsum wallboard lacks water resistance. When it gets damp, it can stay that way, breeding mold and mildew. Conventional wallboard can reduce indoor air quality in areas prone to dampness—like kitchens or laundry rooms—or where there’s sustained moisture, such as showers.
So when they found out that United States Gypsum’s new Fiberock Aqua-Tough panels earned a 10—the highest score possible—on the Association of Standards Materials’ tests for water resistance, the pair was immediately intrigued. Ordinary wallboard scores a zero in the test.