With its idyllic high plains and picturesque Teton mountain ranges, Wyoming is as good a place as any for a vacation retreat. Because this bucolic region receives only about 10 inches to 12 inches of rainfall per year, on average, it may seem like an unlikely place for moisture issues. And yet, it has them.
“Moisture is a big problem here,” confirms Paul E. Duncker, AIA, principal of Wilson, Wyo.-based HandsOn Design. “It's pretty dry and arid in the summer, but because of the intense sunlight and our freeze-thaw cycles, [moisture] works its way into every crevice and joint.”
Truth is, moisture is a fact of life for every house, but it's generally not a problem since wood—the primary material in construction—has a natural capacity to store water. “From a performance perspective, the average home can easily accommodate 45 to 50 gallons of water via hygric redistribution,” writes building scientist and consultant Joseph Lstiburek in “Moisture Control for Buildings,” a February 2002 article published in the journal of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. The larger issue involves how houses get wet, and how they dry.
water pressure Even as building envelopes have tightened in recent years, controlling moisture intrusion into a home remains a problem. Mark Horton, AIA, of San Francisco-based Mark Horton/Architecture, thinks he knows why. “The average residential architect believes in the idea that the house is a simple structure,” he says, but “it's not at all.”
In fact, the average house is vulnerable to moisture intrusion in countless areas. Even wall construction can get tricky. “A technique [that's] effective at preventing moisture from entering an assembly is also likely to be effective at preventing moisture from leaving an assembly,” Lstiburek writes. “Conversely, a technique [that's] effective at removing moisture also may allow moisture to enter. Balance between entry and removal is key in many assemblies.”
It's that very balance that confounds many architects and structural engineers. Jessica Walitt, a project coordinator with McGinnis Chen Associates, has seen firsthand what can happen when buildings aren't thoroughly waterproofed. Her firm, a consultancy with offices in San Francisco and Sacramento, Calif., helps commercial and residential architects and property owners rectify problems stemming from improperly constructed envelopes and exterior details. “A lot of our work involves windows, doors, siding, and exterior components,” she explains.
For architects like Duncker, one of the best ways to avert moisture-related damage in the long term is to design strategically, eschewing certain exterior details that are prone to problems. “I make sure I design the roof geometry to shed moisture efficiently,” he says, “and I minimize valleys where moisture might accumulate.” He also uses a permeable housewrap and a vapor barrier on the inside over the studs, so the house dries from the outside. “It's the old-school way,” he jokes.
Seattle-based Tom Lawrence, AIA, spends a fair amount of time thinking about moisture as well. It's not the volume of rain the region gets that keeps him on his toes, but rather the sheer persistence of it. “It tends to be damp for many months” at a time, the principal of Lawrence Architecture explains, so the siding never really has a chance to dry out. His workaround of choice: rainscreens.
Whitney Powers, RA, NCARB, has taken a similar approach. Her firm, Studio A Inc. Architecture, is located in the low country of Charleston, S.C., not far from the Atlantic Ocean. Moisture-laden sea breezes and wind-driven rain are par for the course, as are humid summer conditions and hurricane threats.
To counter the effects of weather conditions she can't control, Powers has made rainscreens an integral component of most of her recent projects. “We've been putting our siding over furring strips with [Benjamin Obdyke's] Cedar Breather underneath,” she says. She's also “very aggressive” in her use of roof flashing and is extra cautious when specifying corner detailing.
Other architects are quick to acknowledge that past problems early in their careers inspired their current vigilance when it comes to weatherproofing. Horton says drainage problems on one of his first projects forced him to seek remediation. “That's why today, I use a waterproofing consultant on almost every project,” he says.