Why You Need Crawl Space Insulation

Properly installed crawl space insulation is a crucial component of the building envelope. Crawl space insulation is used to separate the conditioned and unconditioned parts of your home. 

Properly installed crawl space insulation can reduce fluctuations in temperature in your home, improve energy efficiency, and result in better air quality. Unfortunately, poorly maintained or improperly installed crawl space insulation can impact the durability, indoor air quality, and energy efficiency of your home.

What is a Crawl Space?

A crawl space is a type of foundation where the first floor of a home is raised about 1-3 feet off of the ground. The crawl space floor may simply be dirt, or it may be covered in gravel or plastic sheeting to serve as a vapor barrier. The purpose of a crawl space vapor barrier is to decrease vapor and moisture getting into the area. That way, your home is better protected from moisture and mold damage. What differentiates it from a crawl space encapsulation is that a crawl space encapsulation completely seals the entire crawl space while the vapor barrier does not.

Crawl spaces are used in areas of the country where soil conditions or moisture prevent other common foundation types, such as slab-on-grade or a basement, from being used. In colder regions, the freeze-thaw cycle can be a critical factor determining which type of foundation you choose. 

Common Crawl Space Problems

Here are some of the most common crawl space issues homeowners face.

  • Ground moisture, water from landscaping, and drainage can seep into your crawl space. Thankfully, this can be remedied by installing a crawl space vapor barrier.
  • Excessive rainfall can cause flooding and standing water. The water typically recedes on its own; however, if you see white marks on the foundation wall, this is a tell-tale sign of recurring standing water in your crawl space.
  • Crawl space insulation problems like falling insulation indicate that your insulation is no longer doing what it should. What’s worse is it acts like a wick, bringing moisture into the sub-flooring. If this happens, you’ll need a professional insulation removal service to remove and repair any damaged insulation.
  • Dark and wet spaces are a breeding ground for mold and mildew. Mold in your crawl space does not only cause a musty odor but can also cause health issues. 
  • The biggest enemy is moisture which creates a whole set of issues when it seeps into the wood and the sub-flooring, causing the wood to warp or curve. You can sort this issue by crawl space waterproofing.
  • Pests in the crawl space. Bugs and rodents in attic can cause a whole host of issues, including damaged foundations, holes, fallen and damaged insulation, etc. It’s critical to find and seal off rodent entry points for pest control. 

Why is Crawl Space Insulation Important?

Crawl space insulation is used as a way to maintain your building envelope when your ground floor is elevated off of the ground. The insulation in your crawl space functions to reduce temperature fluctuations in the conditioned space of your home.

Properly installed and maintained crawl space insulation will:

  • Improve the energy efficiency of your home.
  • Keep your home cooler on hot days and warmer on cold days.
  • Improve the air quality of your home.

How is Crawl Space Insulation Installed?

There are different ways to set up your crawl space, and they can have a big impact on the air quality and energy efficiency of your home. These spaces are usually either a ventilated crawl space or unvented. If you’re installing insulation in a crawl space, the type of crawl space you have will largely dictate where you install your insulation. This will also help you determine the type of insulation you want such as fiberglass insulation or foam. It’s important to understand the difference between a ventilated crawl space and an unvented crawl space before making your next step in the insulation process.

Vented Crawl Space

If your home has a crawl space, it’s most likely vented. Vented crawl spaces have air vents that passively exchange air with the outside. In a vented crawl space, the air in the crawl space is unconditioned. Typically, insulation is installed between the floor joists underneath the subfloor. This insulation constitutes the lower perimeter of the building envelope. Put another way, all of the air above the crawl space insulation is conditioned.

The core issue with vented crawl spaces is that they are often not designed with sufficient moisture protections or a moisture barrier in place. During warmer months, warm air enters the crawl space and cools. As it cools it condenses and forms moisture. If a vapor barrier isn’t used, that moisture condenses on the underside of the subfloor and insulation. If left unaddressed that moisture will form mold on the wet insulation while also leeching deeper into the subfloor, eventually affecting multiple or just one floor joist, your crawl space wall, or the crawl space floor. 

Unvented Crawl Space

If you’re curious about how to insulate a crawl space, the method recommended by most engineers is to treat your crawl space like a mini-basement. This is known as an unvented crawl space. In an unvented crawl space, a moisture barrier is installed along the ground. Some flooring may be installed over that. The walls of the crawl space are insulated, while the subfloor is not. This type of insulation method extends the building envelope downward to include the crawl space in the conditioned space of the home.

Unvented crawl spaces have these key advantages over vented crawl spaces:

  • Better moisture control.
  • Better durability over time.
  • Higher air quality throughout the home.
  • Increase energy efficiency.
  • Less fluctuation in temperature.

Installing New Insulation? Call the Professionals!

If you’ve ignored your crawl space wall insulation for a while, you should strongly consider having a professional inspection done by an insulation contractor. If you’re planning on installing new crawl space insulation, definitely have it done by professionals as well to ensure proper insulation measures are taken.

If the insulation in your crawl space isn’t installed with appropriate moisture mitigation measures in place, you’ll end up having lots of problems down the road. When insulating a vented crawl space you need to have a way to minimize the formation of moisture on the subfloor. Whether this includes a moisture barrier or fiberglass insulation, this will be an important part of a proper insulation process. Additionally, installing insulation in crawl space must be done according to local building codes, which usually includes the use of a vapor barrier to eliminate moisture problems.

Professional crawl space insulation installation will ensure that no air gaps exist that will allow moisture from the crawl space to move upward. This will protect the durability of your home, and result in improved air quality and increased energy efficiency.

Additionally, you may need a crawl space cleaning service done before moving forward with the insulation process. This can help remove mold, wet insulation, or old fiberglass insulation to be sure you have a fresh surface to start new!

Closing Thoughts

If your home currently has a crawl space, consider having it professionally inspected by the crawl space solutions experts at Attic Construction! While it might be easy to ignore your crawl space, ineffective or poorly installed insulation in a crawl space can impact the energy efficiency, durability, and indoor air quality of your home. 

To learn more about crawl space wall insulation, crawl space repair, or to get an expert opinion on the condition of your crawl space insulation, contact us today!



  1. “Guide to Closing and Conditioning Ventilated Crawlspaces” https://www.nrel.gov/docs/fy13osti/54859.pdf
  2. “Crawlspace Insulation” https://www.buildingscience.com/documents/information-sheets/crawlspace-insulation
  3. “Crawlspaces – Either in or Out” https://www.buildingscience.com/documents/building-science-insights/bsi-115-crawlspaces-either-or-out
  4. “Crawl Space Vapor Barriers and Encapsulation” Common Vented Crawl Space Problems https://www.hgtv.com/design/remodel/interior-remodel/crawl-space-vapor-barriers-and-encapsulation
  5. Common Vented Crawl Space Problems https://trianglecrawlspacesolutions.com/crawl-space-problems

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