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, then you might wonder whether it’s worth insulating the crawl space. Is this something you should do?

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

If you still have questions about insulating your crawl space, we’ve got answers. Ahead, we’ll talk further about the above considerations as well as how you should insulate your crawl space and what the benefits are.

Should You Insulate Your Crawl Space?

Crawl spaces are alternatives to basements, but some houses have both. They feature walls and footings under your house, the former of which is usually poured concrete or cinderblocks. Crawl spaces are anywhere from one foot to five feet tall normally.

Most people cannot stand up in a crawl space, so access necessitates crawling. 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. Whether this is worthwhile will boil down to several factors that we touched on in the intro. Let’s delve deeper into those factors now.

Vented or Unvented

Crawl spaces are often unfinished, but some are more complete than others. For instance, yours might feature ventilation. These air vents are built into the foundation wall, usually nearer the top.

The distance from one vent to another allows air to exit the crawl space. Without any form of heating or cooling in the crawl space though, the air that comes in and out is unconditioned and often very moist.

A picture of an unfinished crawl space of a home, with spray foam 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. While it may not cover the entire house, at least most of the surface area is insulated, which does help energy efficiency.

By insulating a vented crawl space, even if it’s just the underside of your lowest floor of the house, you can better control the temperatures in this part of the home. That could in turn reduce the amount of moisture before mold and mildew can develop.

Crawl Space Size

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 very small, then it’s unlikely to cause significant enough temperature changes in your home that it’s going to 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. 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’re going to feel it in the rest of your home. After all, heat rises.

A chilly crawl space on a winter’s day is also going to impact your comfort when you’re at home, so insulating is in your best interest if enough of that cold air is seeping through the floor upwards in to the home, especially since heat rises.

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 that you’re not likely to spend a lot of time in. You wouldn’t know if your crawl space had gaps, seals, or other openings for critters and insects to get into.

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 decide to build their home elsewhere.

Accessibility

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 the whole way through, but not all. If yours gets especially narrow or if the entrance door is really hard to squeeze into, then insulating the crawl space would be difficult.

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.

Which Insulating Materials Should You Use for Your Crawl Space?

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 that homeowners mull over before selecting an insulation material, you also can’t forget that accessibility might be an issue as well.

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

Foam Board

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 can be 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 material and the thickness of the insulation. 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.
This is a good depiction of that foam board looks like 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 having been insulated. 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.

Spray Foam

If you can barely get into your own crawl space, then a technician won’t be able to wriggle their way in there too deep either. 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. 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. Your crawl space will maintain more moderate temperatures that are uninfluenced by outside temps.

Spray foam comes in two varieties, open cell and closed cell. The latter is a harder foam that dries rigidly on a surface. Although its insulating properties are better and its R-value is higher (about 7 per inch of insulation), closed-cell spray foam does not work well in tight areas.

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 really great insulating seal.

Open-cell spray foam applies and dries softer. It won’t provide as thick of a layer of insulation as closed-cell spray foam will, and it’s less water-resistant as well. However, spray foam in general is waterproof and thus 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 as well, if you’d like to check that out here.

Batt or Loose-Fill Cellulose

The third recommended insulating material for crawl spaces is cellulose, especially in batt form. Unlike fiberglass, paper-based cellulose is waterproof, which is integral when putting up insulation in a crawl space.

Made of up to 90 percent recycled materials, cellulose is among the greenest form 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.

Outside of cellulose batts, you could also try wet-spray cellulose, which behaves a lot like open-cell spray foam. Wet-spray cellulose requires water and thus usually a moisture 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.

To read up more and compare cellulose with Rockwool/mineral wool insulation, you can check that out here as well.

Other Considerations When Insulating Your Crawl Space

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

Remove Water

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 too 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. You could use your crawl space for storage rather than waste the space by leaving it empty.

Seal Vents as Well as Openings

We talked earlier about crawl space vents and how they’re usually more trouble than they’re worth. The air quality in your home will be healthier without these vents, not to mention you’ll have fewer outdoor temperature fluctuations to contend with.

Conclusion

Insulating a crawl space is usually beneficial for your home. You can keep out critters and insects, regulate the indoor temperature, and save money on your monthly energy bills. Although no one likes to venture into their crawl space, insulating it now will keep you from coming upon unwanted surprises later!

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