Crawl Space Insulation
The right crawl space insulation depends on how the crawl space is built and where heat and air are moving. Crawl Space Ninja looks at whether the space is vented or encapsulated, which surfaces need insulation, and where air sealing may be needed.
Depending on the crawl space, the solution may include foundation wall insulation, subfloor insulation, rim-joist air sealing, or a combination of methods. The goal is to create the right thermal boundary for the space rather than treating every crawl space the same way.
Do I Need Crawl Space Insulation?
Yes. Crawl space insulation is generally an important part of properly insulating your home, but where the insulation goes depends on how the crawl space is configured.
In an encapsulated crawl space, insulation may be installed along the foundation walls. In a vented or non-conditioned crawl space, fiberglass or rock wool insulation may be installed beneath the subfloor. Air sealing around rim joists and other openings may also be needed to reduce unwanted air movement.
Crawl Space Ninja evaluates the crawl space before recommending the insulation and air-sealing approach. The contractor should also understand the code requirements that apply to your project, especially when insulation is installed as part of crawl space encapsulation.
Crawl Space Insulation and Air Sealing Options
The right approach depends on the conditions found in the space. Through The Ninja Way process, the goal is to match the insulation and air-sealing approach to the conditions found in the space.
Common approaches include:
- Foundation wall insulation for encapsulated crawl spaces
- Fiberglass or rock wool insulation at the subfloor in vented or non-conditioned crawl spaces
- Spray foam or polyurethane caulk to air seal rim joists and penetrations
Foundation Wall Insulation
Foundation wall insulation is commonly used with crawl space encapsulation to create a thermal barrier between the foundation walls and the crawl space. Depending on the project, materials may include InsulBarrier or foam board.
The insulation is installed on block or concrete walls to help reduce heat transfer. The principle is similar to attic insulation: the insulation helps separate conditioned areas from spaces that are exposed to greater temperature changes.
Uneven foundation walls, such as stone or older brick, may require closed-cell spray foam to provide more consistent coverage. When possible, Crawl Space Ninja recommends mechanically fastening foundation wall insulation rather than relying only on adhesives that may lose their bond over time.
Moisture-resistant foundation wall insulation can also be better suited than fiberglass for crawl-space walls where damp conditions are a concern.
Fiberglass Insulation
Fiberglass batt insulation or rock wool is commonly used in vented or non-conditioned crawl spaces.
When outdoor air can move freely through the crawl space, insulation installed beneath the subfloor helps create a thermal barrier between the crawl space and the living area above.
Spray Foam Insulation and Air Sealing
Air sealing is an important part of crawl space insulation because insulation alone does not close gaps where air can move between the crawl space and other parts of the home.
Spray foam or polyurethane caulk may also be used to seal:
- Rim joists
- Plumbing penetrations
- Electrical penetrations
- HVAC penetrations
- Large gaps in exterior block walls
Crawl Space Ninja uses GreenGuard Gold Certified spray foam for the crawl-space air-sealing applications.
Crawl Space Insulation Video
Watch Michael Church discuss the best insulation methods for crawl spaces based on a scientific study. For more informational videos, check out our homeowner tips and guides on our YouTube Channel.
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