Crawl Space Insulation for Cold Climates

Document:

Crawlspaces are a foundation method used in the cold and very cold climates. Two methods are in use for insulating crawlspaces. The first, in common use over the last several decades, is to insulate the underside of the building floor, and provide outside air vents in foundation walls. Research has shown that this approach can lead to moisture problems, especially in areas with cold or humid air. 

Best Practice: A better approach is referred to as conditioned crawlspaces. Within this type of system, foundation side walls are insulated on either the interior or exterior (or both), and no outside air vents tunnel through the foundation wall.

Best Practice: The preferred approach is to install insulation on the exterior foundation wall. Exterior insulation will help to protect the foundation from the freeze-thaw cycle and a warmer wall is less likely to condense moisture. Products such as borate-treated foam board or rigid glass fiber insulation work well. Extruded polystyrene (R-5 per inch) is durable and moisture resistant. Expanded polystyrene (R-4 per inch) is less expensive, but it has a lower insulating value. Rigid fiber glass insulation does not insulate as well as foam but provides a drainage plane. Some code officials may require a gap between exterior insulation and wood foundations elements to provide a termite inspection area. Insulation that is exposed above grade must be covered with a protective coating such as flashing, fiber cement board, parging (stucco type material), treated plywood, or membrane material.

If placed on the interior, wall insulation must extend down the wall to a depth at least two feet below grade level. Polyisocyanurate insulation with an aluminum facing is a good interior insulation choice. If the crawlspace wall extends less than two feet below grade level, then the remaining insulation must be placed horizontally along the ground at the base of the wall. A sealed ground cover is installed over the entire area of the crawlspace. Install a system to provide conditioned air to the crawlspace. More information is available at:

·         Building Energy Codes Resource Center, Details for Mechanically Vented Crawlspaces - Code Notes, www.energycodes.gov/support/code_notes.stm (includes information on sizing the mechanical ventilation).

·         University of Minnesota, Building Foundations Research Program. Minnesota Energy Code Building Foundation Rule: Amendment Proposal Development Project Final Report, www.buildingfoundation.umn.edu/FinalReportWWW/Section-A/A-recs-main.htm

·         www.crawlspaces.org This Web site is geared toward research done on crawlspaces in the mixed-humid climate.

·         See these documents from Building America Consortia available at www.buildingamerica.com in the Publications section:

·         Broniek, John. Builder System Performance Packages Technical Report. Prepared by IBACOS for the Building America Program.

·         Yost, Nathan. May 2003. “The Case for Conditioned, Unvented Crawlspaces.” Building Safety Journal. Also available on the BSC Web site at : www.buildingscience.com/resources/articles/24-27_Yost_for_author.pdf

·         IBACOS. 2002. Best Practices: Consider the Crawlspace.

For more information, please visit Building America or download the full reports below:

Cold and Very Cold Climates

Hot-Dry and Mixed-Dry Climates

Hot and Humid Climates

Marine Climates

Mixed-Humid Climates