What Kind Of Insulation Do You Use In A Crawl Space?

Your crawl space needs insulation. The question is, what insulation should you use? Are there any insulations that don’t belong in crawl spaces? Out of all your options, which insulation is best for you?

South Central Services has insulated hundreds of new and existing homes with spray foam. In our service area, many homes have crawl spaces that need new insulation. Which insulation is best for your crawl space depends on a few factors. There are two good insulation options for crawl spaces and one that should never be used.

By the end of this article, you will understand:

• Why crawl spaces need insulation
• Where insulation can be installed in a crawl space
• Which insulations should be used in crawl spaces

Don't have time to read right now? Check out everything you need to know at a glance.

Why Do Crawl Spaces Need Insulation?

You don’t live in your crawl space, so why does it need to be insulated? Depending on its size, your crawl space is directly beneath some or all of your home. Your crawl space is connected to your living space and is part of your thermal envelope.

Even though you don’t live in your crawl space, its conditions impact your living space. Without proper insulation, your crawl space can contribute cold, musty, and dirty air to your home.

Where Can Insulation Be Installed In A Crawl Space?

Insulation can be installed in a crawl space in two areas: the ceiling or the walls. Which area you insulate affects how your crawl space interacts with your home.

If you insulate your crawl space ceiling, you are cutting off your crawl space from your living space. You create two distinct and separate spaces by insulating the surface that separates your home from the crawl space.

If you insulate your crawl space walls, the idea is to condition your crawl space like the rest of your home. Since there is no barrier between your crawl space and living space, air can freely exchange between these two places. Insulating the walls makes the space more controlled, so attempts to condition the air would be more effective.

Fiberglass Is Often Installed In Crawl Space Ceilings, And It Shouldn’t Be.

Fiberglass insulation is one of the most popular insulation products, including for crawl spaces. Although fiberglass cannot handle moisture, fiberglass batt insulation is often installed in the ceiling of crawl spaces.

Fiberglass batts absorb moisture when in close contact with vapor and moisture. Over time, the fiberglass becomes heavy with water and falls out of the ceiling. When it falls, it is no longer effective as a barrier between the crawl space and the living space.

Even if the fiberglass insulation could stay in the ceiling cavities, fiberglass is not the right product for ceiling insulation. Fiberglass insulation functions by letting air pass through it, absorbing some heat in the process. However, there is still air exchange. The crawl space air is dirty and musty. Fiberglass allows dirty and musty air to exchange with your clean and conditioned air.

You should not use fiberglass insulation in a crawl space.

Closed Cell Spray Foam Can Be Installed In A Crawl Space Ceiling.

If you want an effective barrier in your crawl space ceiling, the product you need is closed cell spray foam insulation. Unlike fiberglass, closed cell can create an airtight seal and form a vapor barrier. Closed cell will not absorb moisture or allow any air to pass between your living space and crawl space.

It will not matter how dirty or musty the crawl space air is because it cannot pass through the closed cell foam.

We recommend this method of insulation when crawl spaces face standing water issues. Crawl spaces with pervasive and unexpected moisture problems must be sealed off from the living space. However, most crawl spaces can have wall insulation instead of ceiling insulation.

Rigid Foam Board Can Be Installed On Some Crawl Space Walls.

For some crawl spaces, rigid foam board is a great insulation option. Due to the rigidity of foam board, flat crawl space walls are the best application. Stone walls with more variations cannot have the foam board lay flat against the wall. Additionally, every seam of the foam boards must be sealed with can foam or caulking.

If you opt for rigid foam board, consider can foam for your crawl space rim joists to ensure that portion of the wall is also sealed off from vapor and cold air transfer.

Closed Cell Spray Foam Can Be Installed On Any Crawl Space Walls.

No matter the crawl space wall, closed cell spray foam is an insulation option. As a spray-applied product, closed cell can adhere to any type of wall with any kind of variation. Closed cell can also be easily installed in the crawl space rim joists.

Like a ceiling application, closed cell offers a vapor barrier and an airtight seal.

We recommend researching crawl space encapsulation when considering any wall insulation for your crawl space. This method also involves a vapor barrier on the floor of the crawl space, but it helps to create a more conditioned space so clean and dry air can be exchanged freely between the living space and the crawl space.

The Bottom Line About Which Insulations Are Used In Crawl Spaces

Fiberglass, foam board, and spray foam are all used as insulation for crawl spaces. Of these three products, only foam board and spray foam are useful for crawl spaces. These two insulations can form a vapor barrier and do not allow cold air to infiltrate the home.

While fiberglass is frequently used in crawl spaces, it should not be installed there. When we are called to fix a crawl space, fiberglass insulation is almost always dripping from the ceiling. Even in its best condition, fiberglass cannot stop cold and dirty air from exchanging with your home. You do not want to waste your expensive conditioned air on your poorly insulated crawl space.

Now that you know which two insulations could be used in a crawl space, your next step is to:

• Discover if crawl space encapsulation is the insulation solution you need
• Learn more about why fiberglass should not be installed in crawl spaces
• Find out if you’ll need to purchase a dehumidifier for your crawl space