Sealing the outside air out and/or conditioning within the crawl space environment is the recommended solution. If insulating the crawl space is a concern, we recommend insulating the foundation walls with polystyrene insulation. You do not need to insulate the ceiling of the crawlspace but check with your local building codes (because although they may not be optimal, or even based on the correct science, they are still the governing say so).

Insulating an Unventilated Crawl Space

According to the U.S. Department of Energy, the best approach to insulating an unventilated crawl space is to seal and insulate the foundation walls rather than the subfloor. In their consumer’s guide to energy efficiency and renewable energy, the advantages to insulating the crawl space are as follows:

• Less insulation required (about 400 sq. ft. for a 1,000-sq.-ft. crawl space with 3-foot high walls.).
• Pipes and ductwork are contained within the house’s conditioned envelope 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 become damaged by rodents, pests, or water (polystyrene insulation can be chewed through by rodents and possibly pests, but should be unaffected by water).
• If radon is present, a radon mitigation system will require ventilation of the crawl space to the exterior (even in a vented crawl space, elevated levels of radon can be present).
• The crawl space must be made as airtight as possible, and the air barrier must be maintained (the CleanSpace crawl space encapsulation system takes this into account with products such as Wall Cap for blocking air penetration from block walls, airtight vent covers for sealing vents, and an airtight crawl space door. Training for CleanSpace Installers includes a video entitled “Air is a Thing” that explains the importance of caulking and sealing off all entry of outside air into the crawlspace.).
• The access door to the crawl space must be located inside the home through the subfloor unless an airtight, insulated access door to the outside is used (Basement Systems EverLast crawl space door is an ideal solution).

Of course we can’t create a vacuum in, nor ever be able to seal out all of the outside air, but the CleanSpace crawl space encapsulation system comes as close as possible.

Sealing your crawl space is the first step. If sealing isn’t enough, then insulation can be installed in the crawl space.