A picture of a crawl space in the bottom of a house with the words Crawl Space Insulation Written? over it.

According to home-buying and selling resource HomeLight, approximately 27 million homes in the United States have crawl spaces.

If your home is among them, you might wonder whether it’s worth insulating the crawl space. Is this something you should do?

For energy efficiency and comfort, it’s usually worth insulating your home’s crawl space. However, considerations such as accessibility, size, and vented versus unvented crawl spaces must be accounted for before you proceed with insulation.

We’ve got answers if you still have questions about insulating your crawl space.

We’ll discuss the above considerations, how you should insulate your crawl space, and the benefits.

So, read on to find out more.

Should I Insulate My Crawl Space?

Crawl spaces are alternatives to basements, but some houses have both. They feature walls and footings under your home, the former of which is usually poured concrete or cinderblocks.

Crawl spaces are anywhere from one foot to five feet tall typically.

Most people cannot stand up in a crawl space, so access necessitates crawling. So now you understand why it’s called a crawl space!

Many homeowners insulate their basements, but the crawl space area may stay out of mind.

A chart showing heat losses from a typical house.
This chart shows typical heat losses from a home. Crawl spaces below a floor can exacerbate losses through the floor, especially if they are not insulated.

Whether insulating a crawlspace is worthwhile will boil down to several factors discussed in the intro.

Let’s delve deeper into those factors now.

Factors Affecting Crawl Space Insulation

Is Your Crawl Space Vented or Unvented?

Crawl spaces are often unfinished, but some leave more to be desired than others.

For instance, yours might feature ventilation and incorporate air vents built into the foundation wall, usually nearer the top.

The vents allow air to enter and exit the crawl space. However, without heating or cooling in the crawl space, the air passing through the vents and circulating in the crawl space is unconditioned and often very moist.

A picture of an unfinished crawl space of a home, with spray foam providing crawl space insulation on the underside of the floor.
You can see towards the top of the photo that the underside of the floor is insulated with spray foam, while the walls are left bare. This layer of insulation helps to improve the energy efficiency of the house.

You can better control the temperatures in this part of the home by insulating a vented crawl space, even if it’s just the underside of your lowest floor of the house.

That could, in turn, reduce the amount of moisture entering your living space, helping to prevent mold and mildew from developing.

Should I Insulate My Crawl Space If It’s Very Small?

The size of your crawl space is another factor that will dictate whether it’s a good idea to insulate it.

If your crawl space is minimal, it could be challenging to insulate because of the cramped working conditions. You’d need to decide whether it was causing significant enough temperature changes in your home that it would drive up your monthly energy bills.

You may want to skip insulating a small crawl space since the payback or comfort benefit may not be there.

Larger crawl spaces could be worth sealing with insulation because, due to their size, the chances of air leaks are much higher.

If too much warm air lingers in your crawl space in the summer, you will feel it in the rest of your home. After all, heat rises.

A chilly crawl space on a winter’s day will also impact your comfort when you’re at home, so insulating is in your best interest if enough cold air leaks through the floor into the house.

Not only will your home be more energy-efficient with insulation, but you’ll feel better knowing that nothing is likely living in your crawl space. No, we’re not talking about ghosts, but critters like mice, rats, and insects.

We mentioned earlier that many crawl spaces are unfinished. They’re also an area of the home where you’re not likely to spend much time. So you wouldn’t know if your crawl space had gaps, seals, or other openings for critters and insects to enter.

Insulation can block off many insects and even animals like mice. The insulation barrier makes it hard for these creatures to get through, so they build their homes elsewhere.

Insulating Crawl Space That Is Hard to Access

A homeowner laying on his side inspects his crawl space with a flashlight
Some crawl spaces are difficult to access, but you can still improve their thermal characteristics to increase comfort in your home and reduce your energy bills.

The last factor that will play a role in whether you insulate your crawl space is how accessible it is.

Some crawl spaces remain the same height throughout, but not all. Insulating the crawl space would be difficult if yours gets exceedingly narrow or the entrance door is tough to squeeze through.

Note how we said difficult but not impossible. You’d be very limited on your insulation options, as you’d be required to use spray foam rather than rigid boards. You could insulate these tight areas, though.

How To Insulate a Crawl Space – Materials Choice

You’ve decided to insulate your crawl space. Now the question becomes which insulating material you should choose.  

While cost and airtightness are usually considerations homeowners mull over before selecting an insulation material, you also can’t forget that accessibility might be an issue.

Thus, while the types of insulation we’ll list in this section work for crawl spaces in general, they won’t all apply to every crawl space.

Foam Board Insulation For Crawl Space

Rigid foam board insulation is one of the premier choices for insulating a crawlspace because it’s waterproof.

As we’ve discussed on the blog before, rigid foam is made of one of several materials. These are extruded polystyrene or XPS, polyisocyanurate aka polyiso, or expanded polystyrene or EPS.

The R-value of rigid foam board is between 1 and 15, depending on the insulation’s material and thickness. Therefore, this insulating material is recommended for cramped and tight spaces, making it ideal for your crawl space.

A picture of a person in a white construction outfit installing rigid foam board insulation on a wood wall.
The above picture is a good depiction of foam board’s appearance when installing it on a wall.

The strength of rigid foam board insulation is another benefit. When added to walls, those walls are usually stronger after insulating.

Although it doesn’t matter as much in a crawl space, foam board is also a great acoustic insulator besides insulating thermally.

Some building codes might require that the foam is covered in fire protectant if the crawl space walls are taller than five feet.

Should I Insulate My Crawl Space with Spray Foam Insulation?

If you can barely get into your crawl space, a technician won’t be able to wriggle their way in there too deep. In these circumstances, installing rigid board insulation will be incredibly difficult, which makes spray foam your best option.

Spray foam, which is comprised of resin and isocyanate, can expand at least 60 times over its original liquid volume. So if your crawl space has a lot of gaps and openings where creepy crawlies are getting through, they won’t be able to after a blast of spray foam insulation.

An awesome thermal insulator, spray foam is also adept at preventing air infiltration. After insulating with spray foam, your crawl space will maintain more moderate temperatures uninfluenced by outside temperatures.

Spray foam comes in two varieties, open-cell and closed-cell. The latter is a harder foam that dries rigidly on a surface. Closed-cell foam has better insulating properties, and its R-value is higher (about 7 per inch of insulation).

A picture of spray foam insulation covering the floor and wood studs in a wall.
Spray foam, when expanded, can fill just about any nook and cranny in your crawl space, creating a great insulating seal.

Open-cell spray foam applies and dries softer. It won’t provide as thick insulation as closed-cell spray foam, and it’s less water-resistant. However, spray foam generally is water-resistant and often suitable for crawl spaces.

The R-value of open-cell spray foam is 3.8 per inch. While you’re taking a hit with the insulating properties, it’s the flexibility and malleability of open-cell spray foam that makes it the more suitable option for crawl spaces that are all but inaccessible.   

We also compare spray foam with fiberglass if you’d like to check that out here.

Batt or Loose-Fill Cellulose For Crawl Space Insulation

The third recommended insulating material for crawl spaces is cellulose. Unlike spray foam, paper-based cellulose is not water resistant, so it might not always be suitable for insulating a crawl space.

Cellulose is made of up to 90 percent recycled materials and is among the greenest forms of insulation. It’s excellent at reducing noise as well as providing thermal insulation.

A picture of grey loose-fill blown in cellulose insulation with a top-down view. It's sitting in between two wood studs.
A great insulator, blown-in or loose-fill cellulose, can be a great option to cover space or inside walls if something holds it in place.

You could also try wet-spray cellulose, which behaves like open-cell spray foam. Wet-spray cellulose requires water and, thus, usually requires a ]retardant to prevent mold.

Wet-spray cellulose might be a gamble in some crawl spaces, but in an unvented one with good moisture control, we’d recommend this insulating material as another one to consider.

In our article, you can read more about the differences between Rockwool and cellulose insulation.

Other Considerations When Insulating Your Crawl Space

After selecting your insulation material, make sure you follow these other recommendations as well.

Remove Water From the Crawl Space

If there’s any water lingering in the crawl space, then the first order of business is to get rid of it. You can use a sump pump or a wet-dry vac to suck up the excess water.

Drainage matting will keep the water out. It’s not a bad idea to run a dehumidifier so the air doesn’t get too moist.

Get a Vapor Barrier Installed If You Don’t Have One

Yes, you can get a vapor barrier retrofitted. This is an especially smart idea if you’re revamping your crawl space.

You’ll be protected from terrible odors, rot, mold, and flooding risks. In addition, improving your crawlspace this way could allow you to use the space for storage rather than waste it by leaving it empty.

Final Thoughts On Crawl Space Insulation

Insulating a crawl space is usually beneficial for your home. You can keep out critters and insects, regulate indoor temperature, and save money on your monthly energy bills.

Although no one likes to venture into their crawl space, insulating it now will help you avoid unwanted surprises later!

Leave a Reply

Your email address will not be published. Required fields are marked *