July 5, 2008
The Smart Vapor Barrier
MemBrain adjusts to control moisture and mold in any season
The next time you plan to remodel or build, you might ask your contractor what he uses as a vapor barrier.
Odds are 10 to 1 he'll say polyethylene, more commonly called "plastic sheeting." And then he'll probably give you one of those you-must-be-crazy looks. It's not often homeowners ask about vapor barriers. Flooring, windows and doors, paint color? Certainly. Vapor barriers? Hardly ever.
But in this day and age, when moisture and mold concerns are gargantuan issues for contractors and homeowners, taking a look at vapor barriers might be a good idea. For the past few years, the building products industry has been developing materials that can better cope with moisture, including mold-resistant drywall.
Now, the industry is looking at how to deal with moisture trapped behind drywall or in the wall cavity of an exterior wall. One of the more interesting products on display at the International Builders Show in Las Vegas last month was CertainTeed Corp.'s MemBrain, the first "smart" vapor retarder for North America. Here's how it works:
During construction of a new home or an addition, a house wrap is commonly used to cover the wood sheathing. After this wrap is in place, an exterior siding - usually brick, vinyl or wood - is installed. The house wrap, a relatively new product, serves two purposes: It is a drainage plain for moisture that gets behind the exterior siding, and it helps block air penetration. On the interior side of the sheathing, fiberglass insulation is placed between studs. On walls that form the exterior outline of the home, this insulation comes with a facing to retard the movement of moisture. In some cases, when unfaced insulation is used, these studded walls, especially in high-moisture areas such as kitchens and bathrooms, can be covered with a polyethylene sheeting. Drywall is then placed over the polyethylene.
"This sheeting is effective at keeping moisture generated from living spaces, like bathrooms and kitchens, from being released through the interior wall," says Tom Newton, a CertainTeed spokesman. What plastic sheeting doesn't address, however, is what happens when moisture is trapped inside the wall cavity. This moisture can condense on cold surfaces and build up between walls, where it can create a breeding ground for mold.
According to Newton, using MemBrain as a vapor barrier alleviates this concern. Because buildings are neither air-nor watertight, water can still get behind exterior siding and through the house wrap. When polyethylene sheeting is used as a vapor barrier, the moisture can be trapped. MemBrain, however, is a polymide film, a nylon-based material that contains pores. When humidity increases, the pores open, allowing water to escape. In winter, when humidity levels are low, the pores are smaller. In warmer, more humid months, the pores are larger, creating a drying process.
What MemBrain does, Newton says, is allow moisture to be released into the interior living space, where it can be recirculated into the home's heating and cooling system.
Smart vapor barriers have been used successfully in Europe for about seven years. German insulation manufacturer Grunzweig & Hartman is credited with developing the first such barrier. It's likely that more North American building manufacturers will launch similar products soon.
Cost shouldn't be an issue either; using MemBrain will add $350 to $400 to the price of an average home, Newton says. The problem might be educating the home builder.
"It is a good product, no doubt about that," says Stacey Dyches, assistant branch manager at Hicksville's Bradco Supply, which caters to contractors and carries CertainTeed products. "Whether the contractor will go for it, that's another question. Contractors and builders traditionally like to work with what they know."
Newton says homeowners with moisture concerns should simply ask their builder or remodeler to use a smart vapor retarder. "What's happened over the years is that we've built homes that are wrapped tighter and have trapped wall systems," Newton says. "This kind of vapor barrier is part of the industry's response."
Copyright © 2008, Newsday Inc.
