How should I maintain my crawl space?
With our tendency to consider things “out of sight, out of mind,” crawl spaces are an area of the house that tends to get neglected. Unfortunately, this also means crawl space problems can go unnoticed until they have an effect on the living space above. At this point, a problem that could have been easily remedied may have progressed into an expensive structural or health-related issue. The crawl space can also present a significant hidden energy drain on a home if not insulated properly.
Good moisture control is the major concern in a crawl space. This starts outside the building envelope, where problems can be stopped in their infancy. Gutters are a relatively inexpensive addition that can provide huge preventative paybacks. In a climate with lots of rain, a house without gutters can direct lots of water against its foundation. Soils, wood and especially concrete are good conductors of water through capillary action. Similar to a paper towel, concrete can soak up water and carry it great distances. If gutters are not an option, then soils around the house should at least be sloped to direct water away from the building.
Once water reaches the foundation, things get a lot tougher. Ideally, both concrete and wood foundations should have some form of waterproofing on the outside. If not, or if it has deteriorated, you may need to consider replacing it.
Assuming all external sources of moisture penetration have been addressed, the next step is to inspect the crawl space interior. Though it may not be obvious, there’s a lot of moisture coming up through the ground. With very few exceptions, exposed dirt floors should be covered and sealed with a continuous vapor retarder such as 6-mil polyethylene plastic sheeting. If the floor will receive traffic, it’s a good idea to use either thicker or reinforced polyethylene sheeting or an even more durable membrane such as EPDM rubber. Even a dirt floor that looks and feels “dry” can release significant amounts of moisture, especially after heavy rains.
Another important consideration is radon, a cancer-causing radioactive gas that occurs naturally in the earth. The University of Alaska Fairbanks Cooperative Extension Service advises that if you have never tested your crawl space or basement, winter is the best time to do so. The negative pressures created by combustion appliances and stack effect can bring radon into the home at a higher rate. Although high radon concentrations are considered hazardous, remediation can be relatively simple. Testing crawlspaces is strongly recommended in areas known to have soils with radon concentrations.
How well a crawl space is insulated and sealed can affect the entire building envelope. In Fairbanks, building codes require foundations to be a minimum of 42 inches below grade to protect the footings from freezing and frost jacking. This can mean you can lose a lot of heat through the crawlspace walls if it is under-insulated. Inspect the foundation walls and floor system closely. If fiberglass insulation was set directly against the inside walls with no moisture protection, or the dirt floor was left exposed, it may be wet and need to be replaced. If the floor joists were insulated, the floor system should be looked at closely. Any exposed ducting should be inspected to make sure all seams are sealed and connected. Be sure that exhaust fan piping (such as dryer ducting) doesn’t just terminate under the floor, but vents directly outside.
If you need to add or replace insulation, rigid foam and spray foam are good options. They both have R-values and also qualify as vapor retarders. If you use foam, especially below-grade, make sure it’s approved by the manufacturer for your specific application. Spray foam and foam board may have certain restrictions or limitations in crawl spaces due to local fire codes. Some brands of foam insulation may meet fire code at a given thickness, while others may not. In addition, it may be possible to use either a coat of fire retardant paint, drywall, or fiberglass insulation to protect the foam board if required. The best source of information regarding current fire code considerations for foam insulations can be found at the local building department. Keep in mind that typically the local fire codes will need to be met if the home needs to be inspected for resale.
Summer is a good time to peek under the floor. The crawl space is integral to the foundation of the house, and in some cases the largest source of unregulated airflow into the home. It is not a good place to let moisture, poor air quality, or bad insulation go unchecked.