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CRAWL
SPACE WALL INSULATION TECHNIQUES
For years, standard building practice was to insulate underneath
the floor over a ventilated, unconditioned crawlspace. A better
approach is to build a well sealed, unventilated crawlspace (i.e.,
build the crawlspace like a basement) by sealing and insulating
the foundation walls rather than the subfloor. Advantages to insulating
the crawlspace walls are:
• Problems associated with ventilating the crawlspace are
avoided.
• Less insulation is required (around 400 square feet for
a 1,000-square-foot crawlspace with 3-foot walls).
• Piping and ductwork are within the conditioned volume
of the house so they do not require insulation for energy efficiency
or protection against freezing.
• Air sealing between the house and crawlspace is less critical.
Disadvantages to insulating the crawlspace walls are:
• The insulation may be damaged by rodents, pests, or water.
• A radon mitigation system will require ventilation of
the crawlspace to the exterior. Not planning for radon-resistant
construction may necessitate air sealing the floor in order to
mitigate the radon through ventilation.
• The crawlspace must be built airtight and the air barrier
must be maintained.
• The access door to the crawlspace must be located inside
the home through the subfloor unless an airtight, insulated access
door in the perimeter wall is built and maintained.
STEPS FOR INSTALLING CRAWLSPACE WALL INSULATION
1. Review plans for this method of foundation insulation with
pest control and local building officials to ensure code compliance.
2. Eliminate or seal the foundation vents.
3. Ensure that combustion furnaces and water heaters located in
the crawlspace are sealed-combustion units equipped with a powered
combustion system.
4. Seal all air leaks through the exterior wall during and after
construction, including the band joist.
5. Locate the crawlspace access inside the home or install an
access through the perimeter that will remain airtight after repeated
use.
6. Select insulation levels in accordance with the International
Energy Conservation Code or the DOE Insulation Fact Sheet. The
Insulation Fact Sheet (DOE/CE-0180) can be ordered from the Energy
Efficiency and Renewable Energy Clearinghouse or accessed from
the Internet at www.ornl.gov/roofs+walls.
7. Install rigid or batt insulation using one of three options
(exterior foam, interior foam, or interior batt) to achieve complete
insulation coverage. Insulate the band joist with batt insulation,
and the crawlspace access if it is located in the wall. Install
a continuous termite shield between the band joist and masonry
foundation wall that covers the wall insulation and extends completely
outside, or leave a 2- to 4-inch insulation gap at the top for
termite inspection.
8. Install a supply outlet in the crawlspace, relying on the leakiness
of the floor to provide the return air path.
Next:
INSTALLING UNDERFLOOR INSULATION
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