PROPER WAY TO FINISH BASEMENT WALLS IN A HEATING CLIMATE

(a heating climate is where you spend more money on heating your home in the winter than money spent cooling your home in the summer)

UNFINISHED BASEMENT WALLS – If the studded walls in the basement are left unfinished with only fiberglass insulation and visqueen (aka vapor barrier or plastic sheeting), there is a strong potential of moisture/mold problems. During the winter months, we create substantial moisture in our homes and buildings. This moisture usually cannot escape to the outside as we tend to keep our windows and doors closed during the heating months. When the visqueen is installed without any covering, it is not air tight as air can leak around seams, edges, and fastener holes.

The warmer and more humid air becomes in the basement, the higher the vapor pressure. The colder and dryer that the outside air becomes, it reduces the vapor pressure. Once we start getting vapor pressure differentials, the moist air in the basement penetrates the openings in the visqueen layer. It continues traveling through the very porous fiberglass insulation and meets up with the cold wall sheathing. From here, it will condense, turning it into liquid water. Once we have physical moisture on the inside of the wall cavity, the insulation and visqueen prevent the moisture from drying or evaporating. This moisture can then cause decay and mold problems.

The best way to correct this problem is to immediately install gypsum wallboard (or equivalent) over the visqueen (visqueen should only be installed above grade) and paint it with a latex paint. The latex paint will act as a sufficient vapor retarder. Before the gypsum wallboard is installed, it should be embedded in a sealant around the perimeter to act as a gasket to help prevent airflow into the cavity.

INSULATED BOX SILL – It is very common to insulate the box sill area of a basement due to the high heat loss in this area. It frequently is done improperly by using merely fiberglass batt insulation (faced or un-faced). Without a true vapor barrier in place, we can have the same conditions as listed under “UNFINISHED BASEMENT WALLS” above. If the box sill area is left exposed or only protected with a tile ceiling (non gypsum wallboard), great care should be taken to prevent air flow into this cavity. This is best protected by installing rigid foam insulating board over the insulation to make it air tight. The combined R value of the insulation and rigid foam insulating board should be at least equal to the R value of the wall above. The rigid foam board should be carefully fit, then sealed around all 4 edges with a sealant.

*All of the above information is trademarked and is the property of RESTORx. We feel it is the most current and accurate information available but we do not guarantee it be the only proper solution. Written by Stephen Gitz, CR, WLS, CMP