There's a growing trend toward the use of unventilated and conditioned crawl spaces. As one insulation expert pointed out, “We don't ventilate basements, and crawl spaces are just short basements.”
Here's what the U.S. Department of Energy has to say:
“Most building codes require vents to aid in removing moisture from the crawl space. However, many building professionals now recognize that building an unventilated crawl space (or closing vents after the crawl space dries out following construction) is the best option in homes using proper moisture control and exterior drainage techniques.
“If you have or will have an unventilated crawl space, the best approach is to seal and insulate the foundation walls rather than the floor between the crawl space and the house. This strategy has the advantage of keeping piping and ductwork within the conditioned volume of the house so these building components don't require insulation for energy efficiency or protection against freezing. The downside of this strategy is that rodents, pests or water can damage the insulation, and the crawl space must be built airtight and the air barrier maintained.”
So, if you have an unventilated crawl space, then you'd want to insulate the crawl space walls instead of the floor. But what you really need to keep in mind with unventilated crawl spaces is that the crawl space needs to be airtight, and it needs to remain that way. So here are a few tips:
• Install a well-sealed 10-mil vapor barrier on the ground. Lap the seams, extend it up the walls, and seal it to the walls. As an alternative, consider putting down a concrete slab. You need to do everything possible to keep moisture out of the crawl space.
• Seal the rim joist and any penetrations to prevent air and moisture from getting in. Make sure no rain or snow can get into the space.
• Install ductwork to condition the space.
Remodeling and repair questions? Email Paul at firstname.lastname@example.org. All product reviews are based on the author's actual testing of free review samples provided by the manufacturers.