BY: Ilya Benesch, Cold Climate Housing Research Center
Energy Focus: Fairbanks Daily News-Miner September 18th, 2008, Section A3
Crawl spaces are one of those areas in the house that tend to get neglected. The old adage “Out of sight out of mind” might apply here. Unfortunately, this also means that crawl space problems can go unnoticed until they progress into more expensive structural or health-related issues. The crawl space can also present a significant energy drain on a home if not insulated properly.
Good moisture control is a primary concern. This starts outside the building envelope, where many problems can be stopped in their infancy. Gutters are a relatively inexpensive addition to a house that can provide huge preventive paybacks. A house without gutters may direct a lot of water against its foundation. Soils, wood, and especially concrete, are good conductors of water—picture a paper towel soaking up water, concrete works the same way. If gutters are not an option, then the ground around the house should be sloped to direct water away from the building.
Once water reaches the foundation, things get a lot tougher. Therefore, the structure must be prepared to resist infiltration. Both concrete and wood foundations should have some form of waterproofing on the outside.
Once all external sources of moisture penetration have been addressed, the next step is to inspect the interior of the crawl space. With very few exceptions, exposed dirt floors should be covered and well sealed with a continuous vapor barrier such as 6 mil polyethylene. Without a good ground barrier, moist crawl space air will condense on any cold surface. Even a dirt floor that looks and feels “dry” can release significant amounts of moisture, especially after heavy rains.
Testing crawl spaces for radon is also strongly recommended. Radon is a cancer causing radioactive gas that occurs naturally in the earth. If you have never tested your crawl space or basement, the cold seasons are the best times to do so. Although high radon concentrations are very hazardous, remediation after detection can be relatively straightforward. Test kits and information are available through the Cooperative Extension Service at 474-1530.
How well a crawl space is insulated and sealed can affect the entire building. Interior Alaska building codes require foundations to be 42” below grade to protect the footings from freezing and frost jacking. Anything above that point stands a good chance of being frozen solid during the winter, causing serious heat losses if the crawl space walls and rim joist areas are under insulated.
Inspect the foundation walls 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 replacing. If the floor joists were insulated, then the floor system should be looked at closely. Any exposed ducting should be inspected to make sure that all seams are sealed and connected. Be sure that exhaust fan piping doesn’t just terminate under the floor, but vents directly outside.
If you need to add or replace insulation, rigid foam and sprayed foam are good options. These types of insulation have very high R values, and also qualify as vapor barriers. If you use foam, especially below grade, make sure it is approved by the manufacturer for your specific application. Also, if they are exposed inside the structure, most unfaced foams are required to be fire protected for code compliance.
Tomorrow would be a good time to peak under the floor. The crawl space is integral to the foundation of the house, and in some cases the largest source of unregulated air flow in to the home. It is not a good place to let moisture, poor air quality, or bad insulation practices go unchecked.
Ilya Benesch is the Building Educator at the Cold Climate Housing Research Center (CCHRC). For questions or comments please contact CCHRC at (907) 457-3454
I have an older house that had some smoke damage in the crawl space from a elecytical fire. A local Co. stripped the crawl space of everything. They put down a new 6mi. vapor barrier 6″ of glass on the crawl space floors ( including all sills and headers. They then also insulated the floor that sits on the crawl space. The crawl space is vented in the summer and sealed off in the winter
I have been told not to insulate wlls and floor both do to lack of ventalation.
If I put a vent from the main floorto the crawl space and put a fan on a timer at the vent that goes outside, would this work
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