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Vented vs.
Sealed Crawlspaces
A friend is building a new house and will have a sealed crawlspace. Is this a better option for controlling termites and mold?
A home built on piers or concrete blocks has a crawl space between the bottom of the floor and the ground. This area is just large enough to "crawl" under, in most states clearance is 16 inches or higher. It differs from construction used in a home with a basement or a home constructed directly on a concrete slab. Most crawlspaces have foundation vents on each side to allow air circulation for moisture control. Some homeowners install aftermarket temperature-controlled vents that open automatically in warmer weather allowing air flow and close when temperatures are below freezing to protect plumbing and water pipes. Your friend is referring to a completely sealed crawlspace without any ventilation outside. Sealing is done either by enclosing the entire crawlspace barrier with insulation, encapsulation process or simply not installing any foundation ventilation. Often this is done to save energy.
The process of encapsulating a crawl space includes sealing off foundation vents, covering the ground and foundation walls with plastic, and blowing Styrofoam™ insulation throughout the entire crawl space. From a pest control inspector’s perspective, sealing a crawl space inhibits the ability to do a visual inspection for termites and other pest or rodent infestations. The sealant and plastic may hide termite shelter tubes, powder post beetles, other wood infesting beetles, wood decay fungus and damages associated with these pests. Since yearly termite inspections are essential in preventing termite damage and upholding termite warranties, sealed crawl spaces may affect termite warranties.
Sealed crawlspaces are a relatively new idea and I spoke with technical representatives with Temp-Vent ® Corporation, the manufacturer of various foundation ventilators and a leader in automatic foundation vents. They agree traditional, un-vented crawl spaces may encourage biological contaminations such as mold and other fungi but according to the EPA, the only way to control mold growth is to control moisture. In any crawl space, plumbing and air conditioning leaks are probable.
Again, from a pest control perspective, a properly ventilated crawl space will reduce the potential for moisture related problems as long as the crawl space soil is higher than the exterior soil level (to prevent standing water under your home). Also exterior soil should be sloped or graded away from the house on all sides to permit water runoff away from the home. Ensure all gutters, downspouts, and overflow drain lines divert water away from the exterior walls of your home. All exhaust vents (dryers, bath exhaust fans, kitchen exhaust fans) terminate outside your house and not into the crawl space, where they could leave excess moisture.
Also recommended is a durable vapor barrier (6 mil plastic) to cover the entire floor of the crawl space and maintenance of plumbing systems regularly to ensure that any leaks are addressed promptly. Avoid the use of landscaping and mulch directly against your home's exterior which could contribute to moisture problems in the crawl space.
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