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Vented to Unvented Crawl Space

Converting a crawl space from vented to unvented can reduce utility costs while improving comfort, indoor air quality, and durability.

The crawl space shall be inspected for any evidence of bulk water penetration, moisture or pest damage, and a list of any potential problems shall be provided to the homeowner before proceeding with the work so remediation can be fully addressed as necessary. The contractor shall verify proper foundation drainage and foundation waterproofing/damp-proofing before proceeding.
If the crawlspace ground level is below the surrounding grade, perimeter drainage shall be provided.
Sufficient access shall be provided. A minimum 16x24-inch airtight, insulated access door shall be installed in the perimeter wall. If below grade, a minimum 16x24-inch threshold is also required. Alternatively, a minimum 18x24-inch access hatch shall be installed through the floor inside the home.
Remove any existing insulation and replace any rotting wood. All wall surfaces shall be cleaned of any dirt or debris.
A minimum 6-mil-thick polyethylene sheeting shall be installed over the entire ground with a minimum lap of 6 to 12 inches and no tears or holes. In addition, the polyethylene sheathing shall be extended a minimum of 6 inches up all foundation walls and concrete footings and taped for a continuous seal. Note: the ground shall be cleared of all vegetation and organic material before installing the ground vapor barrier.
All sealants used shall be compatible with their intended surfaces and meet fire rating requirements around flues. Maximum gap dimensions shall be consistent with manufacturer’s specifications.
Foundation wall vents and other penetrations shall be blocked and sealed. If required, some vents may be replaced with flood vents that include weather stripping to reduce standby air infiltration.
For fire safety, the International Residential Code requires that all penetrations through the framed floor be sealed. Some jurisdictions may require a non-porous sealing product.
Cripple walls, rim joists, and foundation walls shall be air sealed and insulated to an R-value that meets or exceeds the 2012 International Energy Conservation Code. Insulation must meet ignition barrier requirements.
All rim joists adjoining the exterior shall be insulated with high-density closed-cell foam sprayed directly against the rim joist or with rigid foam that is cut to fit and sealed in place with caulk or canned spray foam.
Foundation walls shall be insulated with either spray foam or rigid foam insulation.
If using spray foam, high-density closed-cell or medium-density open-cell foam shall be sprayed directly on the entire surface of all foundation walls adjoining the exterior.
If using rigid foam panels, they shall be attached to the interior of the foundation wall with construction adhesive applied in a serpentine pattern. When using two layers of foam, stagger the seams. These panels shall completely cover all crawlspace wall surfaces with no air gap between them and they shall be fully in contact with the masonry wall, with no gaps. Panel seams shall be fully sealed with caulk, foam, mastic, or flashing tape that is specified as acceptable by the rigid foam insulation manufacturer.
HVAC supply and return air flow to the crawl space shall be provided at a rate of 1 CFM/50 square feet of crawl space floor area.
Water intrusion shall be monitored after the work is complete and any necessary repairs shall be made.
After completion, a combustion safety test shall be performed if any natural draft combustion equipment exists in the crawl space to ensure there is no back-drafting or spillage of combustion emissions.
The home shall be inspected for the presence of a whole-house ventilation system. If one is present, the actual air flow shall be tested and verified to meet ASHRAE 62.2 capacity. If the home has no whole-house ventilation system, or if the existing system does not meet the ASHRAE 62.2 requirements, recommendation shall be made to the homeowner to either install a new system or repair an existing system to be ASHRAE 62.2-compliant.
If the conversion was done as part of a radon mitigation package, at the completion of the work, a radon test kit shall be provided to the homeowner to verify radon levels are within EPA acceptable levels.

BASC Guides

Information guide describing how to assess crawlspaces and basements before proceeding with upgrades in existing homes.

Guide describing methods for insulating an unvented crawlspace or conditioned basement with rigid foam on the interior side of the walls to provide an insulated space for HVAC equipment.

Guide describing how to upgrade a crawlspace floor in an existing home by adding insulation.

Guide providing information about treating bulk water drainage issues and moisture control measures in existing basements and crawl spaces.

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert (HIE) is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

  • Be the Expert: Take advantage of Building America Solution Center comprehensive guidance on ‘Existing Home’ retrofits.
  • Earn Trust: Inform homeowners how your work conforms to U.S. Department of Energy (DOE) world-class expert guidance and recommend homeowners visit the DOE website as evidence these are indeed official best practices.
  • Clarity with Contrast: Tell prospective homeowner clients to compare your expert recommended best practices with other contractors.
  • Ensure Equivalent Pricing: Tell prospective homeowner clients to insist other bids also include DOE checklists to ensure equivalent quality work.
  • Translate Value: Note your company uses DOE HIE Checklists based on world-class expert recommendations for home improvements on all your public-facing communication including websites, advertising, and signage.
  • Create Emotional Experiences: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images for good and bad insulation and air sealing; pre- and post-energy bills following quality installed work; short and long warranties for standard and high-efficiency equipment; and charts showing amounts of contaminants in homes that can be reduced with effective fresh air systems.

Vented to Unvented Crawl Space Background

Unvented crawl space

To convert a vented crawl space to an unvented crawl space, in all of the vent openings and air sealing and insulation are installed at the exterior walls instead of at the underside of the floor above. As a result, the crawl space becomes part of the conditioned space of the home. This provides a temperate space for heating and cooling equipment and ductwork located in the crawl space so it will last longer and operate more efficiently. Sealing off the vents, insulating the walls, and covering the ground with a vapor barrier that is sealed to the walls also helps to reduce potential moisture problems by keeping out humid outside air and moisture vapor from the ground. As an added benefit, the conditioned crawl space can provide climate-controlled storage space.