When finishing a basement, do it the right way

House Doctor | Gary Dymski

August 25, 2005

Finishing a basement is no big deal. For years, American homeowners have been expanding their living space by turning basements into recreation rooms, kitchens and even bedrooms.

But the way Andy Engel tells it, we've been doing it all wrong for a long time. I couldn't agree with him more.

Engel, a contractor and journalist, remodeled a basement in Bridgeport, Conn., and wrote about his project in the March issue of Fine Homebuilding magazine. Engel's article, "The No-Mold Finished Basement," guides homeowners - and contractors - on how such conventional materials as drywall, rigid foam board and wood studs, can be used and how a basement can remain mold-free.

"I wanted to show that if we just fine-tune our building practices and use the same materials we've always used, we can beat moisture issues," said Engel, who since the March article has become an editor at Fine Woodworking magazine.

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Because I'm interested in turning my barren, poured-concrete basement into living space some time soon, I've been researching new materials and techniques for basement remodeling. But I'm finding that, unlike Engel, many contractors are doing this the same old way. These people are using plastic vapor barriers to trap moisture, and that, according to experts, is a fatal mistake.

"The key to dealing with mold issues is not trapping moisture," said Engel, whose building experience ranges from remodeling kitchens and bathrooms to new home construction. "Using permeable materials, like polystyrene, allows moisture and vapor to move through the material. If you can combine permeable materials and the proper level of dehumidification, a finished basement shouldn't develop water issues."

In the last few years, manufacturers of building materials have introduced a wave of new products, including mold-resistant drywall, in response to moisture problems. Although the new materials have yet to prove they can stand the test of time, experts seem to believe they work. The problem is that many of these new materials are much more expensive than the traditional ones.

That's one reason Engel stuck to the usual materials. He also made another significant adjustment: He eliminated a vapor barrier. For many years, below-grade - or basement - remodeling has included a plastic vapor barrier. This thin plastic sheeting traditionally has been installed on the interior (warm) side of the insulation. The barrier kept moisture from getting inside the living area. For example, a stud wall with fiberglass batts installed between the studs was covered by a vapor barrier of thin plastic sheeting. The plastic would be stapled to the studs and then the wall would be finished with drywall or paneling. Instead of using a barrier, an impermeable material like plastic sheeting that traps moisture, today's contractors are recommending installation of a permeable membrane. This membrane allows moisture to escape wall and ceiling cavities. Once moisture escapes it can be removed with dehumidification.

Engel's choice was simple polystyrene, or rigid foam. The project began with sheets of 2-inch-thick rigid foam being glued to the concrete walls and floor. In addition to its insulation properties, the semipermeable polystyrene layer also will prevent wood-stud walls and plywood subflooring from contacting the concrete and absorbing moisture. A seam tape was used to seal the foam seams. After a subfloor of half-inch plywood was installed over the polystyrene, walls built from wood studs were lifted into place. To finish, traditional drywall was then screwed into the studs.

"The only material I was on the fence about was using steel studs," Engel said. "But I am a carpenter by trade and I prefer wood over steel. Every time I work with steel studs, I get my hands all cut up."

Engel said that he could have used newer materials, such as moisture-resistant drywall and permeable membranes that prevent moisture from being trapped in wall cavities.

"It's not that I am against these materials," he said. But making alterations in how we build, he said, is more important than the materials we are using.

After completing the basement, Engel said his final step was to use a dehumidifier. "Dehumidification varies from house to house," he said. "I would not be finishing a basement if I had any serious water problems, where water was coming into the basement."

Engel said in his experience, he rarely finds that a basement needs its own heating or cooling system. "If the basement is just damp or smells a little musty, generally, a properly sized dehumidifier works just fine."

Order Andy Engel's article "The No-Mold Basement" at FineHomebuilding.com. Back issues are $7.99 each, plus $3.50 shipping and handling.

A slow finish

If you are building a new home, contractor/journalist Andy Engel advises putting off finishing your basement. It's not a bad idea, he said, to give the house at least a year to settle. Once you're sure there are no water issues, go ahead and remodel the basement.