Finished Wall and Floors

Hiding concrete or block behind new walls is the easy part. Building walls that won't encourage mold and mildew, or be damaged by condensation, is a lot harder. Because concrete in contact with the ground is always cool, it can become a condensing surface for water vapor in the warm air escaping from a finished basement. The result? Damp building materials, mildew and, eventually, rot. Air will be musty, finished surfaces ruined. As Massachusetts builder Fred Unger puts it, "If you get a hack to do the work, it's going to smell like gym socks."

Unger, like other contractors, isolates damp concrete walls from the rest of the space with 1 in. of extruded polystyrene insulation, followed by a layer of 6-mil polyethylene. On rough walls, foam insulation can be sprayed on. Impermeable layers of foam and polyethylene separate wall framing from damp concrete or block while giving water vapor no cool surface on which to condense. Other builders may skip the polyethylene vapor barrier even if they use foam insulation.

Joe Stanton, a Rhode Island builder, for example, thinks it makes more sense not to build walls too tight. It's safer, he says, to give walls a way of drying out should any water or condensation collect inside. Fears of trapped moisture also prompt some remodelers to use light-gauge steel framing on outside basement walls. Although builders might differ on these details, they would agree that obvious water problems, such as leaking foundation walls, must be solved first.

Despite their moisture problems, below-grade surfaces often don't need as much insulation as exterior walls built above ground. Even in winter, the temperature of the earth below the frost line might be no colder than 55° or 60°F. As a result, some builders simply skip fiberglass insulation in stud walls if they use rigid or sprayed-on foam.

Alure Home Improvements, a Long Island, New York, remodeling company, uses an entirely different approach in creating finished basement walls. Its growing basement business relies on a wall-finishing system developed by Owens Corning. The system uses fiberglass panels and trim pieces that snap into PVC structural framing

Wall panels are finished in fabric, eliminating the need for drywall taping or painting. Carl Hyman, the company's owner and president, says the system is up to 30 percent more expensive than conventional drywall construction but has a longer life span and easily tolerates the damp conditions found in basements. Maintenance costs, he says, also are lower. Any parts of the system that become wet or damaged can be removed. Despite its practical advantages, the system does not look like a typical wall and might be a tough sell esthetically in some parts of the country.

When it comes to flooring, just about any material will work — tile, carpet, vinyl or laminate. Fewer contractors, however, choose conventional hardwood flooring because moisture in the slab could cause the wood to swell and buckle. Remodelers should apply a masonry sealer before installing any finish floor. Eldrenkamp uses a fairly elaborate system of polyethylene, rigid-foam insulation, 153 sleepers and tongue-and-groove plywood to create a floating-floor system — that is, a floor not directly attached to the slab. It makes for a warm, dry finished floor, but built-up floor systems such as this may not be possible in basements with extra-low ceilings.

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