How To Insulate A Crawl Space

Your crawl space needs insulation. You've noticed drafty floors, high energy bills, or a musty smell in your home. You know your crawl space is to blame. But which insulation product is best for your crawl space? Are there tips and tricks you should know before you start?

South Central Services has insulated hundreds of homes with spray foam. In southern PA, many homeowners are concerned about their crawl spaces. Our team is well-versed in crawl space issues and how to solve them.

By the end of this article, you will understand:

• How insulation functions in a crawl space
• What insulation methods we recommend for crawl spaces
• Which insulation product should never be used in a crawl space

What You Need To Know About Crawl Space Insulation

For crawl space insulation to be functional, it needs to do one of two things:

1. Create an environment that is clean and dry
2. Cut off the crawl space environment from the living space

If the environment becomes clean and dry, it doesn't matter if air passes between your crawl space and living space. However, if the crawl space remains dirty, musty, and wet, you do not want that air exchange with the air in your home.

Knowing these two potential goals, how can you insulate your crawl space?

We Recommend Encapsulation For Crawl Spaces

The encapsulation method creates a clean and dry environment. We prefer encapsulating because the technique allows us to control the variables in crawl spaces that lead to mold and mildew odors.

When we encapsulate a crawl space, we install the following products:

• 12 to 20 mil plastic sheathing
• Dimple mat
• Professional-grade crawl space tape
• Closed cell spray foam insulation
• Dehumidification system

After encapsulating, a crawl space is cut off from the outside elements. The only air exchange is between the crawl space and the living space. Encapsulation makes the air clean and dry, so the air that exchanges is of the same quality.

Can Encapsulation Be Done DIY?

Encapsulation can be done yourself. Many websites sell DIY crawl space encapsulation kits. You can also learn about the materials needed for a successful DIY and purchase them yourself.

DIY encapsulation most often uses 12 mil plastic sheathing, foam board, professional-grade crawl space tape, and can foam or caulking.

The plastic sheathing is installed on the crawl space floor. Any seams of the sheathing are sealed with tape. These seams could include the edges of the crawl space and around crawl space pillars.

Foam boards are installed on the walls, and seams are sealed with can foam or caulking.

We do not recommend DIY encapsulation for crawl spaces with irregular walls. If your walls are not flat, foam board is not the best option for your crawl space. Stone and masonry walls are often too textured for foam board to lay flat.

Another Option Is Crawl Space Ceiling Insulation

You can cut off the crawl space air from the rest of the house by insulating the crawl space ceiling. This is not our preferred method because it leaves a crawl space musty and damp. However, this is sometimes the best option for some crawl spaces.

For example, crawl spaces with standing water need ceiling insulation instead of a vapor barrier on the floor.

We use closed cell spray foam when insulating a crawl space ceiling. Closed cell spray foam creates an airtight seal and a vapor barrier, preventing icky crawl space air from escaping and circulating with conditioned living space air.

Can Ceiling Insulation Be Done DIY?

We do not recommend doing ceiling insulation yourself. Spray foam insulation is the only effective barrier between the crawl space and the rest of the house.

While spray foam insulation is sold in DIY kits, we do not recommend using these kits for any project greater than 100 square feet. DIY kits don't save money on spray foam materials and offer incredibly limited control of chemical reaction variables.

Professional contractors spend tens of thousands of dollars on equipment to monitor these variables. The resulting foam could be off-ratio if these variables are not monitored and controlled.

In addition to our usual reservations about DIY spray foam kits and their performance, the crawl space ceiling offers additional challenges.

Even for seasoned spray foam professionals, spraying overhead is challenging. The foam's overspray lands directly on your respirator face shield, obstructing your vision.

How Not To Insulate Your Crawl Space: Fiberglass Batts

Most crawl spaces in our service area are insulated with fiberglass batts. This batt insulation often hangs out of ceiling cavities or lies uselessly on the crawl space floor.

Even if the batt insulation was snug in the ceiling cavity, fiberglass offers poor performance compared to spray foam.

Fiberglass allows air to exchange. While closed cell spray foam can create an airtight seal and vapor barrier between the crawl space and living space, fiberglass lets air infiltrate uncontrolled. Unless there are no gaps in the faced fiberglass insulation, it cannot offer a vapor barrier.

Fiberglass also absorbs moisture. Over time, the gaps in the vapor barrier allow fiberglass to absorb and become heavy with moisture. Eventually, the batt insulation falls out of the ceiling and offers no performance at all.

Batt insulation installed perfectly with no gaps still cannot compete with the airtight seal of spray foam. In real-world applications, batt insulation is ineffective and becomes a nest for rodents.

The Bottom Line About How To Insulate Your Crawl Space

The crawl space is part of your home's thermal envelope. When you insulate your crawl space, you must either separate it from your living space or convert it to a conditioned, clean, and dry environment.

Encapsulation cleans and dries the crawl space, while ceiling insulation isolates it from the rest of the home. DIY crawl space insulation is sometimes possible, but we recommend working with a professional contractor to ensure the best results.

Now that you understand how you could have your crawl space insulated, your next step is to:

• Learn whether encapsulation is worth investing in
• Discover if you could encapsulate your crawl space as a DIY
• Calculate how much professional encapsulation might cost you