Eliminating Moisture in Walls
Air barriers keep buildings dry and energy-efficient
By Brett Martin
"Water worms its way in through failed mortar joints, gaps where the wall meets the roof and foundation, and from wind-driven rain," Henry says. "On warm, humid days, warm, moist air can find its way in through those same pathways, until it drops its moisture on cold pipes or on drywall cooled by air conditioning. [In] hot or cold weather, wet walls have reduced R-value, which kicks up heating and cooling costs. And, of course, wet walls are susceptible to mold."
Addressing Moisture ProblemsInsulation often is placed over an air barrier to make buildings more energy efficient, says Dave Polk, president of Epro Services Inc. in Derby, Kan. In this construction method, the air barrier has to be non-permeable to keep any moisture from passing through the masonry wall to the building's interior.
"The idea is make the building water and air tight," Polk says.
When insulation is placed inside the masonry wall, the air barrier has to be permeable to allow moisture vapor to pass through it, he says.
"The [goal] is to keep moisture out of the building, but if it gets in, the air barrier allows moisture to get out in the form of vapor," he says. "You want to have a permeable, or what we call 'breathable,' barrier, so condensation will [pass as] vapor through it to the outside of the building."
"It's not a straight path," he says. "That warm, moist air passing from inside to outside through that torturous little path is letting energy escape. You're letting your energy dollars escape just like if you left a door or window open."
Condensation can also create problems, Henry explains. As warm, humid air leaks through gaps in walls into the wall cavities and meets cold surfaces chilled by the cold outside air, condensation occurs, just like on a glass of ice water in a warm room./p>
"That warm moist air is going to try to find its way to the cold dry air," Henry says. "It will try to get out any hole, like penetrations in the wall."
Air barriers stop that air from moving through the wall cavity, he says.
Managing Moisture with Air BarriersAir barriers need four things to be effective, otherwise they can make the moisture condition worse, Henry says. They have to be continuous, so air doesn't escape at seams; durable so they stay in place until the brick is installed; breathable so vapor can pass through; and structural so they adhere to the sheathing and can't detach from it.
Epro Services has an air barrier membrane called Ecoflex that can be rolled or sprayed onto buildings. The barrier is placed in wall cavities of commercial buildings, like schools, between the CMU and the brick façade, Polk says.
Ecoflex is self-sealing and adheres to almost any substrate, including damp block, to prevent air leakage. It also seals leaks caused by penetrations in the wall and cracking due to building movement and shrinkage, Polk says. Ecoflex comes in both a permeable and non-permeable formulation.
(Right) This opening in the masonry veneer lets warm moist air into the building envelope. If it finds its way through the structural wall, there is danger of condensation in the cooler recesses of the wall assembly. Condensation creates conditions for mold and other wall-component deterioration. Air barriers stop the air flow at the structural walls. Photos courtesy of PROSOCO.
"Our products are made with a non-woven plastic mesh. They're designed to have water drain through them, not absorb the water," Atkins says, explaining that CavClear spreads out moisture along the fibers. "Because you've now increased the surface area of the moisture, it's going to dry faster."
CavClear prevents excess mortar from blocking weep holes, allowing moisture to pass through the wall properly, she says. It also provides protection against mold, mildew and other moisture-related problems, and it can be used with other air barriers.
"CavClear lets air and water flow through the air space for good drainage and ventilation," Atkins says. "If you're building with brick, a product like ours is going to provide ventilation to the air space behind it and prevent moisture-related failures."
Understanding and Installing Air BarriersAir barrier installation is typically straightforward, such as rolling or spraying the barrier onto the wall, so masonry contractors can install it while building masonry walls.
"The masonry contractor is typically the installer of air barriers since the mason is erecting the block walls, then they're applying the brick façade," Polk says.
Even if masonry contractors don't apply the air barriers, they need to understand how the systems work, Henry says.
"It's important for a masonry contractor to be well educated about all aspects of the wall," Henry says. "The masonry contractor has to know what's going on with the wall, so he knows how to respond if there's a problem."
For example, if he notices the air barrier coming loose before he starts laying brick, he'll know there's a problem that can lead to moisture and mold.
"The masonry contractor has to realize he could be one of the first people who gets blamed if there's a problem, even if he had nothing to do with it," Henry says. "He could fairly quickly put investigators right, but who needs to spend time doing that to begin with?"
If the masonry contractor spots a problem, he can inform the general contractor, he adds. "Like it or not, the masonry contractor is going to have some connection to the way that wall performs."
Keith Lolley, VP for Advanced Building Products Inc. in Springvale, Maine, points out that proper flashings are needed with air barriers.
"Remember, air barriers are not through-wall flashings and do not take the place of through-wall flashings," Lolley says. "Installing a metal drip edge with an air barrier-type product in a flashing application will heat up the air barrier, causing it to drool and stain the surrounding masonry. Current rubberized asphalt air barriers are not UV resistant."
Advanced Building Products recently invented a non-asphaltic copper flashing, Copper Sealtite 2000, that's UV resistant and compatible with all air barrier systems for use at the base of walls, over doors and windows, and any other obstruction, he says.
About the Author
Brett Martin is a freelance writer located in Shakopee, Minn. with several years of construction and writing experience.