When temperatures drop, the crawl space under your home plays a bigger role than most people realize. Without the right insulation material, cold air can move in fast, leading to frozen pipes, high utility bills, and cold floors. Improving crawl space insulation is one of the most effective ways to boost energy efficiency, control moisture, and improve indoor air quality.

What to Use in a Crawl Space

There are several options depending on the layout and needs of your space. Using a mix of these can help with moisture problems, better temperature control, and reduce heating costs:

  • Fiberglass batts are affordable and easy to install between floor joists.
  • Spray foam insulation creates a tight seal that blocks air and moisture.
  • Foam board insulation works well on foundation walls and provides a long-lasting thermal barrier.
  • Plastic vapor barriers keep ground moisture out, especially in dirt-floor crawl spaces.
Fully encapsulated basement crawl space.
Adding a plastic vapor barrier is helpful for spaces with a dirt floor. Credit: Grandbrothers / Getty Images

Benefits of Crawl Space Insulation

  1. Improve energy efficiency. Proper insulation along the ceiling and joist bays improves energy loss, leading to a lower carbon footprint. With a well-insulated crawl space, an energy audit would show that it's easier and more efficient for your furnace to regulate indoor temperatures.
  2. Prevent frozen pipes. Minimizes the likelihood that pipes or sump pump freeze or burst during cold weather due to uninsulated walls.
  3. Prevent mildew and mold growth. Both plastic vapor barriers and spray foam insulation create an air-tight seal that eliminates ground moisture penetration, especially in an unvented space. The barrier reduces moisture buildup and prevents water damage. Vapor barriers also help with dirt floor crawl spaces, effectively making the area a more usable space without standing water. These moisture barriers do more than keeping your crawl space dry. They regulate humidity levels, prevent the buildup of moisture and make it easier to control mold and mildew growth.
  4. Enhance Indoor Air Quality. Reduces the entry of pollutants and allergens. By sealing gaps and preventing drafts, winterization can improve your IAQ.
  5. Protect structural integrity. Using closed-cell spray foam guards against moisture damage and is dense enough to reinforce structural elements. A layer of batt insulation can't do that. This type of insulation can be used on the walls and serve as insulation between floor joists to eliminate air leaks.
  6. Increases comfort. Crawl space insulation will help you maintain a more consistent temperature inside your home. Rigid foam board insulation panels are great for the concrete walls of your foundation.
  7. Pest Prevention. Sealing entry points and insulating the crawl spaces with cellulose insulation can help you avoid rodent and pest inspections. They won't be likely to gnaw through spray foam insulation.
  8. Preserves HVAC system efficiency. With better insulation around your heating ducts, the HVAC system doesn't have to work as hard to maintain the desired indoor temperature, leading to increased system efficiency and longevity.
  9. Long-term cost savings. Insulation upgrades aren't always cheap, but by preventing issues such as mold removal and remediation, moisture damage, and frozen pipes,  winterization can lead to long-term cost savings on repairs and maintenance. It can even reduce the likelihood of foundation repairs! A more efficient home will also lead to lower energy bills.
  10. Home value preservation. A well-maintained and properly winterized crawl spaces can help maintain building codes. Insulated walls also contribute to the overall integrity of the home, preserving its value over time.

Man checks attic crawl space insulation to make sure it's properly insulating.
Should You Replace Old Cellulose Insulation in Your Attic?
Outdated insulation can impact your home’s energy efficiency and comfort.
Read More

When to Consider Crawl Space Encapsulation

If your home has vented dirt crawl spaces, or if you’ve seen signs of moisture-related damage, mold, or pest infestations, crawl space encapsulation may be the best option. It involves sealing the entire space with a heavy-duty liner and vapor barrier. Some systems also include dehumidifiers or crawl space drainage solutions for added moisture control.

Foam vs. Fiberglass: Which Insulation Is Better?

Spray foam insulation gives the best air seal and moisture resistance. It’s often the top choice for rim joists and foundation wall coverage. Fiberglass insulation is more budget-friendly and easier for DIY crawl space insulation jobs, but it doesn’t provide the same air sealing or water vapor barrier benefits.

Wooden shelves installed to become a home's basement pantry.
What’s the Best Way to Insulate Basement Walls?
The right insulation can keep your basement dry, comfortable, and energy-efficient year-round.
Read More

FAQ

How thick should crawl space insulation be?

Insulation thickness depends on your climate zone and local building codes. In most areas, aim for R-13 to R-19 in the floor and R-10 or more on walls.

Is a vapor barrier the same as encapsulation?

No. A vapor barrier only blocks moisture from the ground. Crawl space encapsulation includes a vapor barrier, but also seals vents and walls for complete moisture and air control.

Can I install insulation myself?

DIY crawl space insulation is possible with fiberglass batts or foam board. Spray foam is best left to professionals due to safety concerns and equipment needs.