A crawl space is defined as a type of basement that is so shallow you cannot stand up. Specifically, it is the area between the ground and the floor of the structure above. It may or may not be sealed off from the outside by a cinder block wall or other framing; generally there is a perimeter wall for the sake of appearing more finished. The distinguishing feature, and the one that causes problems is that the floor of a crawl space is earth.

Crawl space waterproofing presents unique problems within a residential home. In order to keep ground moisture vapor from rising up into the home and creating structural damage you must seal it off. Short of the very expensive solution of creating a finished basement beneath an existing house, how do you “seal” the ground while at the same time permitting it to serve as usable storage space?

In the past, a layer of Visqueen (a trademarked brand of polyethylene sheeting) was simply placed over the earth to serve as the crawl space vapor barrier. This is effective in the short run, preventing water vapor from rising into the structure of the house to some degree. Inevitably though, it develops cracks and is dislodged due to foot traffic and item storage. Another method that was often utilized was to build vents into the crawl-space walls. The thinking was that air circulation would force the moisture in the crawl space air to end up outside. Testing proved this to be wrong; in fact, lower humidity levels were achieved in a closed environment that had utilized proper crawl space repair techniques than one that was vented. Obviously, winter temperatures are also more easily controlled without the openings.

Without question, much of the remedy is a floor and wall vapor barrier. Crawl space dynamics have resulted in fiber reinforced membrane materials that effectively contain soil moisture. If this membrane is installed properly, it will be attached to the walls with overlapping seams of at least six inches. Also, due to the “stack effect”, warm air in a home rises and then leaves through the upper walls and attic. The home then replaces that warm air with cooler air sucked up from the crawl space below, which penetrates from the earth and crawl-space walls. So, sealing the walls in addition to the floor keeps the moisture and soil gases from entering the home in the first place.

There are many other benefits to crawl-space waterproofing. Moist air provides the perfect breeding environment for dust mites, roaches and spiders, not to mention molds and bacteria. Ultimately, larger vermin are also discouraged as they feed on the insects that in turn, feed on the mold and mildew. Your home is not the ideal place for the food chain to proliferate!

Aside from the “ick” factor, the negative effects of moisture on the structure of the house can get expensive and dangerous. Flooring boards expand and buckle, rot permeates beams and joists, condensation occurs on insulation, water pipes and ductwork, humidity increases in living areas raising heating and air conditioning costs and electrical-mechanical systems deteriorate. All of this decreases the value of the home.

If your crawl space is not presently sealed, contact a fully insured and licensed foundation waterproofing and repair company. The best ones will generally come out to the house and perform a free inspection and prepare an estimate for the repairs.