Why You Need Crawl Space Insulation

There are several reasons why crawl space insulation is a worthy investment for a homeowner. In sum, crawl space insulation mitigates damage caused by moisture and the extra cost caused by air inefficiently leaking and mixing between the crawl space and livable space. Though moisture and energy efficiency may seem small on a day-to-day basis, either one of these variables can generate larger problems and costs down the line if not managed properly. As a homeowner gains or maintains equity in a house, it behooves them to keep that equity in optimal condition. Crawl space insulation facilitates this goal without much extra cost or complications.

Open vs Closed Crawl Space

First, we come to open vs. closed crawl spaces. Both styles can serve as a foundation for the house as well as a storage space. Closed crawl spaces are designed to be within the thermal envelope of a house, thereby automatically reducing some of the moisture and efficiency problems that can impact open crawl spaces. However, homeowners should not get a false sense of confidence and consider insulation for even a closed crawl space.

Moisture Control

A crawlspace may not be sealed”perfectly, so a vapor barrier covering fiberglass insulation should be installed. Remember that concrete can develop cracks over time. Combined with soil moisture permeation, condensation and/or leaks, even a closed crawl space can produce mold and generally cause problems. Open crawl spaces have an extra variable to consider: cooling from the home’s HVAC system. Hot outdoor air can hold a lot of water vapor, so its relative humidity is low. When that hot air blows into a cooled crawl space, it cools but the moisture content per unit volume of air doesn’t decrease. Relative humidity shoots up and condensation soon follows. With condensation and generally high moisture, bugs and mold degrade wood subflooring. Additionally, rust can form on exposed metal parts, making future repairs or alterations much more complex and costly than they would be with preventative measures such as crawl space insulation.

Energy Efficiency

A related reason for installing crawl space insulation is simple efficiency. A sealed crawl space is extra air in the house that is heated and cooled as much as the living space. Just as open windows decrease efficiency of heating or cooling and lead to larger bills, a crawl space without insulation is effectively the same thing. You may have heard of parents yelling to their kids to “Close that window, we’re not trying to air condition the whole street!” Yes, but a crawl space is not quite as easy to close, though the savings will be larger when you do. As you may have guessed, an open/vented crawl space generates this issue to a greater extent than a closed crawl space. But, again, as with moisture control, homeowners with closed crawl spaces should not grow complacent and ignore the efficiency and cost benefits of insulation.


Crawl spaces can be ideal foundations for a home. They reduce the risk of concrete cracking and uneven settling that plaques slab foundation structures. On the flip side, they are cheaper and simpler to build than full basements while still providing ample storage space even if livable space square footage is modest. Though builders are cognizant of homeowners’ concerns about moisture and high heating/cooling bills, crawl space insulation may not be ideal, especially over long time periods. Homeowners who supplement crawl spaces with insulation such as fiberglass and polyurethane vapor barriers will have extra protection against the whims of extreme weather, soil moisture, and eventual wear-and-tear that affects crawl space construction.

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