While a majority of homes have a full basement there are a number which include attached crawl spaces. Not to mention those that have no basement at all just a crawl instead.
Unlike a full basement a crawl space was never intended to be anything more than access to the heating and plumbing or maybe rough storage best. That being said adequate ventilation was not a concern in the design of most crawl spaces.
Sure there are a number of smaller vents incorporated into the top rim of the foundation in key locations around the crawl. However it is left up to the home owner to open and close these with seasonal changes. More often than not over time the vent assembly itself rust or deteriorates to such a degree that it is no longer functioning.
There are two basic types of crawl spaces those with concrete slabs and those with dirt floors.
Most home owners believe that just because they have the concrete floor slab they have taken care the problems. Not so. Concrete itself is natural porous and will allow the moisture to bleed through. The presence of wall cracks only exasperates the issue. However without proper ventilation that moisture will create condensation and higher levels of humidity. Higher levels of humidity breeds mold. Left on treated mold starts to destroy the integrity of the general structure including the wooden floor joist above. As the air from the crawl naturally rises into the upper living areas it brings all that humid, moldy air with it creating that uncomfortable and unhealthy musty odor.
Dirt crawl spaces are even more susceptible to this issue since the soil itself will never dry completely it provides an added source of moisture speeding up the growth of mold and other bacteria.
By containing the source of these problems below a heavy duty vapor barrier a quality crawl space encapsulation is one of the most cost effective remedy to these problems. While the applications for a dirt and cement crawl space are slightly different the premise is the same.
All existing vents are sealed shut, this will eliminate seasonal changes in air temperature and humidity. Next the space between each of the rim joist are filled with a foam insulation. Any areas of water egress are repaired. An epoxy injection treatment is used to treat wall cracks and a interior drain tile with sump is needed when hydro-static pressure is the problem. A heavy duty re-enforced polyethylene vapor barrier( 12 to 20 mils) is installed in two stages. The first application will extend from just below the sill plate down to and across the floor. The second piece is laid across the floor overlapping the wall membrane. To be truly effective all over laps and thru barrier penetrations are sealed with a seam tape.
All of the same rules apply for dirt slabs with the following changes.
A perimeter drain tile and sealed sump to remove the moisture in the soil are a must. To help vent soil gases a passive air movement system is installed by tapping into the drainage line with a series of through wall vents. To help encourage air movement a solar powered fan is installed in conjunction with the venting drawing the contaminated air out of the home.
A felt paper is laid over the tile and soil prior to the vapor barrier going down. The small opening in the felt will aid in air movement under the vapor barrier. While some companies will install a high capacity de-humidifier we suggest the use of an E-Z breathe ventilation system to help remove any remaining moisture and gases. When lower air temperature in the crawl is of great concern a foil backed insulation is installed to the underside of the floor joist above.
Don’t let the moisture in your crawl permeate your home with a damp and musty smell contact
Written by Walter Slowinski