Insulating an Unventilated Crawl Space
If you have or will have an unventilated crawl space, then your best approach is to seal and insulate the foundation walls rather than the subfloor. The advantages of insulating the crawl space are as follows:
* You can avoid the problems associated with ventilating a crawl space.
* Less insulation is required (around 400 square feet for a 1,000-square-foot crawl space with 3-foot walls.)
* Piping and ductwork are within the conditioned volume of the house so they don’t require insulation for energy efficiency or protection against freezing.
* Air sealing between the house and the crawl space is less critical.
The disadvantages of insulating a crawl space include the following:
* The insulation may be damaged by rodents, pests, or water.
* A radon mitigation system will require ventilation of the crawl space to the exterior. Not planning for radon-resistant construction may necessitate air sealing the floor to mitigate the radon through ventilation.
* The crawl space must be built airtight, and the air barrier must be maintained.
* The access door to the crawl space must be located inside the home through the subfloor unless an airtight, insulated access door in the perimeter wall is built and maintained.
Source: EERE, U.S. Department of Energy