Barriers to Entry

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.

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.

Visible moisture is one thing, but the moisture you can't see can be just as problematic. “The below-grade stuff is even harder to figure out,” Horton says. “It comes from all directions.” That's why basement water-proofing and other below-grade considerations are so important, he adds.

Luckily, a number of manufacturers have developed products to help minimize the guesswork. Reynoldsburg, Ohio-based Tremco Barrier Solutions, for example, claims its Tuff-N-Dri waterproofing system keeps the foundation wall temperature closer to the air temperature of the basement, minimizing condensation and controlling moisture.

For the vulnerable areas under windows and doors, Wylie, Texas-based Carlisle Coatings & Waterproofing has introduced EZ-Pan, a sill pan flashing assembly comprised of a sill wedge, flashing, and pre-molded polyethylene corner pieces. The system reportedly provides a continuous water barrier and drainage plane—even in a sill's vulnerable corners.

Delta-Dry, a heavy-duty polyethylene membrane from Cosella-Dörken Products of Beamsville, Ontario, is another option. The system's dimple-and-groove design helps drain water and acts as a capillary break. It's also said to be impermeable to both air and moisture.

Products such as WeatherTex housewrap (above), Cedar Breather roofing underlayment, Delta-Dry polyethylene membrane (shown below), and plastic/rubber flashing panels make it easier for architects to keep moisture at bay. Using proper construction techniques and building for your region are still highly recommended.

Just this year, Reno, Nev.- based Fortifiber Building Systems Group introduced WeatherTex, a hybrid product that combines its Super JumboTex building paper and WeatherSmart nonwoven, nonperforated polymeric housewrap. The manufacturer says the weather-resistant barrier can be used in any climate and with any cladding.

Other new products include DuPont's Tyvek AtticWrap, a breathable membrane that helps reduce air leakage through the roof; Gorilla Wrap nonwoven, nonperforated housewrap from Denver-based Johns Manville; and an inventive line of plastic/rubber flashing panels for plumbing, electrical, gas, and HVAC exterior protrusions from Quickflash Weatherproofing Products in Las Vegas.

Even with all these options, there's no quick fix to be had and no substitute for sound construction practices. Wall assemblies and construction techniques should be chosen based on the climatic conditions of your area. While this may seem elementary, Lstiburek writes that it's not unusual to find “cold” climate building envelope designs used in “warm” climate regions.

Delta-Dry polyethylene membrane

“Building assemblies, in all climates, can get wet from the exterior by both liquid flow and capillary suction (rain, dew, and groundwater as moisture sources),” he explains. “Accordingly, techniques for the control of liquid flow and capillary suction are similar in all climates and are interchangeable.”

However, he warns, “building assemblies get wet by air movement and vapor diffusion in different manners depending on [the] climate and time of year. Therefore, techniques for the control of air movement and vapor diffusion are different for each climate and are seldom interchangeable between different geographical locations.”

Bottom line: There's nothing wrong with pushing the envelope in design, if you honor the local laws of Mother Nature.