Article #118 - Does the Energy Code Allow an Unvented Crawlspace?

Closed crawlspace with insulation.

Although historically, some codes have included ventilation requirements for crawlspaces in homes, the energy code does allow both vented and unvented crawlspaces. For either type of crawlspace, you should be aware of some code requirements (2000 I-codes):

Vented crawlspace requirements:

• The raised floor over the crawlspace must be insulated to the code R-value requirements for floors (varies by location).
• A vapor retarder may be required as part of the floor assembly (varies by location).
• Ventilation openings must exist that are equal to at least 1 square foot for each 150 square feet of crawlspace area and that are placed to provide cross-flow (IRC 408.1, may be less if ground vapor retarder is installed).
• Unconditioned crawlspace ducts must be sealed and meet R-value insulation requirements (IECC Table 503.3.3.3) - usually R-5.

Non-vented crawlspace requirements:

• The crawlspace ground surface must be covered with an approved vapor retarder (e.g., plastic sheeting).
• Crawlspace walls must be insulated to the R-value requirements specific for crawlspace walls (IECC 602.1.7, 502.2.1.5, and Table 602.1).
• Crawlspace wall insulation must extend from the top of the wall to the inside finished grade.
• Crawlspaces must be mechanically vented (1 cfm per 50 square feet) or conditioned (heated and cooled as part of the building envelope).

If you live in a region with a different set of codes, check with your local code official to determine the code requirements in your area.

A good option for many homes today is building an unventilated and conditioned crawlspace, as this technique can reduce duct losses, lower risk of freezing pipes, keep moisture out, and may reduce construction costs. For more information about building an unvented and conditioned crawlspace, see the DOE Technology Fact Sheet on Crawlspace Insulation.

For more information about building an unvented and conditioned crawlspace, see the DOE Technology Fact Sheet on Crawlspace Insulation, or Details for Mechanically Vented Crawlspaces - Code Notes.