Crawl Spaces

Houses are built on foundations, concrete slabs, or on crawl spaces. Depending upon where you live the soil and weather may be such that it is not possible or practicable for a foundation. In the south homes are usually built on concrete slabs or crawl spaces. Crawl spaces are a narrow area that sits between the ground and the subfloor of the house, usually two to four feet in depth. For most houses crawl spaces are enclosed with masonry foundation walls with an entrance from either the outside or inside of the home. A crawl space is unfinished space that is vented to the outside. The crawl space may have a concrete floor, but often it is left as simply an earth floor.  Crawl spaces are notorious for causing moisture problems to the home when not properly ventilated or insulated.

Frequently utilities are located in the crawl space such as electrical wiring, plumbing pipes, and often the main heating unit. They are usually dark, dirty, and humid areas that provide natural breeding grounds for rodents, insects, mold, mildew, and wood rot. A crawl space can be useful space if properly vented and insulated.  

Venting crawl spaces is critical for protecting the longevity of a home from moisture damage. Mildew due to ground moisture builds up in crawl spaces and has the tendency to condense onto crawl space framing and the subfloor sheathing surfaces above, which over time can lead to rot and threatens the overall structural integrity of the home. Proper ventilation will prevent the crawl space moisture buildup and insulating the subfloor above with moisture barrier insulation will prevent the subfloor from rotting.

Normally crawl spaces have several rectangular vents dispersed around the crawl space foundation. The vents are designed to be opened and closed depending on weather conditions. When the weather is moist they should be open allowing air to move through the crawl space. A more complete solution to resolve crawl space moisture problems is to prevent the ground moisture from entering the crawl space. One way to do this is to install a vapor or moisture barrier on the floor of the crawl space. The crawl space moisture barrier should partially fold up the sides of the crawl space foundation wall and be fastened to the wall. Another solution is to lay a vapor barrier on the crawl space ground and pour concrete on top of it. This will eliminate nearly all the moisture coming from the ground.