Heat the Space: How to Insulate a Garage

As a general rule, there are few or no regulations about insulation in your garage with the exception of walls that adjoin the house. For a freestanding garage, you don’t need any insulation at all as long as the structure meets local and national codes. Of course, need and want are two very separate issues.

After all, maybe you do most of the work on your vehicles yourself. In that case, you may decide that it’s a good idea to insulate for your comfort. That still leaves the pesky question of how to insulate a garage.

If you’re thinking you want to insulate a garage, keep reading for our guide on how to do it.

Reasons to Insulate a Garage

The regulations about walls between a garage and the interior of the house should prove good enough to keep your home warm. Bear in mind, though, that insulation won’t regulate temperatures in a space by itself. Insulation maintains the temperature in any given space.

If it’s cold outside, it’ll remain relatively cold in the garage. If it’s hot outside, it’ll likely be hot in the garage.

The primary reason for insulating a garage is that you want active temperature and humidity control in the space. For example, you may own a classic car or store fragile items in the garage. Temperature and humidity control will help preserve the vehicle or family belongings.

The other primary reason for insulating a garage is that you work in the garage regularly. For example, you may maintain a small woodshop in your garage. Temperature control will help you stay comfortable, protect your tools, and protect any wood you store.

Selecting Insulation

Whether you’re insulating an attached garage or insulation a detached garage, you must consider the insulation options.


For the DIYer, the most common option is fiberglass insulation. It’s a widely available insulation and you can use it on the walls and ceiling. It also requires very few tools, such as a basic utility knife and a staple hammer.

Rigid Foam

Rigid foam comes in large four-foot by eight-foot sheets. Again, a utility knife will serve you well for thinner sheets. You can score the board and simply snap the two pieces apart.

For thicker sheets or long cuts, you can also use a jigsaw or even a circular saw. Use eye and breathing protection if using a powered saw. Rigid foam works for garage doors as well. If your garage door isn’t in proper working order, you can get DIY garage door parts for repairs before insulating.

Spray Foam

A final option is polyurethane spray foam. Most homeowners prefer letting professionals handle spray foam, but you can get kits for your use.

How to Insulate Garage Walls

Garages come in a variety of materials. Let’s work from the assumption that your garage uses wood frame construction with vertical studs every 16 inches or every 24 inches in the center. The variance will depend on when your home was built and who built it.


Let’s also assume you pick the most economical option with fiberglass insulation. Fiberglass comes in 15-inch wide and 23-inch wide options. That means you just cut to length and press it between the studs.

Faced fiberglass also comes with paper tabs on both sides. You unfold the tabs and staple them to the front of the studs.

Rigid Foam

With rigid foam insulation, you must cut for length and width. You should cut the board slightly smaller than the available space between the studs or you can break the board by putting it into place. You must also cut out areas to get the foam around outlet boxes and switch boxes.

Once you get the foam cut, you must gently press it into place between the studs and against the exterior wall. You’ll want some expanding foam to seal any gaps around the edges.

Make sure you check on the local code requirements to find out if you need a vapor barrier in place as well.

How to Insulate a Garage Ceiling

Insulating a garage ceiling is very similar to insulating a garage wall. In the case of the ceiling, you’ll probably find fiberglass or spray foam insulation the easiest option.

You’ll likely find the fiberglass easier to maneuver at the ceiling level than rigid foam. It’s also much easier to push into place and form around any junction box, such as a ceiling fan junction box.

If you go with a DIY spray foam kit, the spray foam will adhere to the space between the rafters. These options help reduce the odds of falling off a ladder as you work since you can typically remain centered on the ladder as you work.

How Much Does It Cost to Insulate a Garage?

The overall cost of insulating a garage will vary pretty drastically depending on several factors. The first major factor is simply the size of the garage itself. A one-car garage is typically 12 feet by 20, while a two-car garage is typically 24 feet by 24 feet.

All of that extra square footage means more insulation.

The choice of insulation also affects the cost. Spray foam garage insulation can run over $1000 for a two-car garage space. Fiberglass insulation will likely only run you a few hundred dollars.

If you hire a contractor, you’ll also need to include labor in your estimate. In that case, the cost can swell into the thousands.

Should You Insulate Your Garage?

The choice to insulate a garage depends on your needs. If you spend a lot of time in that garage during the cold weather, then insulation and heating the garage makes sense. The same holds true if you plan on storing vintage cars or delicate family belongings.

If you’ll only spend time in the garage occasionally and won’t store anything delicate in the garage, insulating will probably end up something of a wasted investment.

Looking for more home improvement tips? Check out the articles in our Interior Design section.

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