Many homeowners ask us, “What is the best way to insulate my crawl space?” That depends, is your crawl space open or closed? Are you looking to air seal or create a thermal break or both?
Best Way to Insulate Closed Crawl Space
If your crawl space is closed or encapsulated there are several ways to insulate. We recommend foundation wall insulation as recommended by the Department of Energy. Foundation wall insulation comes in several forms. Foam board, spray foam, or insulation vapor barrier are the most commonly used for crawl space encapsulation projects. But we have seen contractors install fiberglass on foundation walls. This is not recommended.
Choosing the Right Foundation Wall Insulation
The type of foundation wall insulation you choose depends on the type of wall, budget, and if you will hire a crawl space contractor or do it yourself. Brick or stone crawl space walls are insulated differently than block or concrete. DIYers may not have the fastening tools of a contractor and could choose to use an insulation vapor barrier. Whatever method you choose, make sure it will last and consult a professional if needed to help you decide.
Attaching the Foam Board Insulation
There are several ways to attach foam board insulation to the cinder block or concrete walls. Some installers use a foam board adhesive while others attach the foam board using screws or masonry nails. Since adhesives can fail over time, we recommend screws or nails. It is also a good idea to spray foam the joints of the foam board. Similar to mudding drywall in order to prevent moisture from escaping from between the panels. Here is a video showing how Crawl Space Ninja attaches foam board.
Insulating Open Crawl Space
When the crawl space is open or vented it is also open to moisture, high humidity and whatever nature throws at it. The best way to insulate your crawl space when vented is to install fiberglass batt insulation in the sub-floor. This way the sub-floor becomes the thermal break to help keep the cold crawl space air from transferring to the living space.
Crawl Space Insulation: Open vs. Closed Considerations
Closed crawl spaces keep cold and hot air out. Open crawl spaces allow cold or hot air to enter the crawl space. Other materials like rock wool and spray foam can be used to insulate the floor of your crawl space. Keep in mind floor insulation can trap moisture from a leak or high humidity. We try to stay clear of covering the entire sub-floor with insulation because we are typically closing crawl spaces. But focusing on air sealing major sub-floor gaps is recommended whether your crawl space is open or closed.
Air sealing the crawl space is a great way to make your home more comfortable. Drafty homes are homes with little to no air sealing. Most insulation installed in homes built today do very little to air seal or reduce drafts. Many insulation contractors are focused on R value or type of insulation.
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Other Recommended Articles
Here are 3 more crawl space insulation articles to help improve your homes energy efficiency.
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