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What is the Best Way to Insulate a Bonus Room Above a Garage?

bonus room insulation | garage insulation

What is the Best Way to Insulate a Bonus Room Above a Garage? Blog Feature
Amanda Ringler

By: Amanda Ringler on August 17th, 2020

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That room above your garage has now become one of the most important rooms in the house.

Whether it’s becoming a room for your first child or the master bedroom, procrastinating about fixing this uncomfortable room over the garage has come back to haunt you.

With more than 17 years of experience under our belts, RetroFoam of Michigan has come out to homes where that bonus room over a garage was in desperate need of an air seal – which foam insulation can provide.

Stop dealing with extreme temperatures that are 10 degrees hotter or colder depending on the time of year, smells, noises, and high monthly electric bills. To fix these issues, let’s take a look at the best way to insulate a bonus room above a garage.

Best Way to Insulate a Bonus Room Over a Garage

The best way to insulate the finished room over the garage is going to be just like any other room in your house – insulate the exterior walls, the ceiling or attic, and the floor.

The options you have for the room, in general, are fiberglass batts, blown-in cellulose, blown-in cellulose, injection foam, and spray foam.

Now let’s talk about each section of the room and the best way to insulate it.

Cathedral Ceiling or Attic Insulation

Do you notice ice dams on the roof above the bedroom over the garage in the winter, and it’s impossible to keep it cool in the summer?

You probably have little to no insulation in the ceiling or attic of your bonus room.

The way to insulate the ceiling will differ depending on whether it is a cathedral ceiling or actually has an attic.

For a cathedral ceiling, your options depend on the amount of remodeling you want to do. You could update the fiberglass batts that are already up there. Another option could be adding spray foam insulation.

If you went with the fiberglass batt option, then the drywall ceiling would need to be removed, and the batts would be stapled into place. Keep in mind, fiberglass doesn’t create an air barrier, so you will lose air through the roof.

If you choose spray foam, which is our preferred method, panels would be cut out of the ceiling, and the foam would be sprayed into each cavity. The drywall would be replaced, and a rough patch of mud spread across the seams.

Spray foam insulation creates an air seal that will keep you from losing treated air through the ceiling.

Now, if your bonus room has an attic, your options are a little different. You could opt for spray foam, fiberglass, or cellulose.

Cellulose can be either a loose-fill or blown-in insulation in this application. The material is installed on the floor of the attic and must be maintained as it is known to drift to one side or the other as air movement happens.

The other option for the attic above your bonus room is fiberglass. The fiberglass batts need to be cut to perfectly fit into the cavities of the attic flat. If not, then even more air will leak out through the attic.

Spray foam insulation can be sprayed either on the roof deck or the flat of the attic. The roof deck creates a sealed building envelope of the space and makes the attic part of the conditioned space of the home. If you decided to insulate the attic flat instead, it would seal the attic off from the rest of the house.

While foam insulation is the more expensive option in either application, it is the only material offered that creates an air seal. That air seal stops air movement and will help lower those monthly energy bills.

Exterior Walls Insulation

When we come to a home to insulate the bonus room, we find that there is nothing in the walls at all, which is contributing to your uncomfortable room.

All of those drafts coming in through the outlets and windows will make your AC unit and furnace work overtime because this room is 10 or more degrees hotter or colder than the rest of your home. That’s a pretty big temperature difference.

Your options for the exterior walls are injection foam and blown-in cellulose. Both are installed similarly with holes drilled into the stud cavity of the wall from the outside, with no need to tear out the drywall.

One thing to keep in mind is the cellulose will settle over time, which will leave areas in the wall with no insulation coverage. While the injection foam is a more expensive option, the material will completely fill the cavity creating an air seal. You will also save money on monthly energy bills, which will pay you back in the long run.

Insulating the Floor Over an Unheated Garage

The floor of your bonus room is probably the most forgotten about area, and the spot that will give you the most trouble when it comes to extreme temperatures.

Your garage probably isn’t heated or air-conditioned, which means whatever temperature it is, your bonus room will be too. Not to mention the smells and noise that come from a garage.

So how do you insulate a floor over a garage? You have two options for the ceiling of your garage, which is the floor of your bonus room – spray foam and fiberglass.

The fiberglass batts can be cut to fit the cavities of the garage ceiling. They have to be cut so they fit perfectly into the cavities. Keep in mind, fiberglass is known to retain allergens and pollutants, so whatever comes into the garage will permeate the fiberglass, and will affect your bonus room.

Spray foam can be installed on the underside of the bonus room floor in the garage. The benefit of spray foam for this area is its sound dampening qualities. Spray foam will also help keep the temperature regulated as it will cut off the air from the garage making its way into the bonus room.

The Right Bonus Room Insulation Will Fix a Cold or Hot Room Above the Garage

The only insulation material that creates the air seal you will need to keep your bonus room comfortable is foam insulation.

Traditional insulation will still allow not only for air movement into the space, but also the odors from your garage and moisture. That moisture can lead to the growth of mold and mildew, which can turn into a bigger problem to deal with.

If you’d like to learn more about the benefits of foam insulation for your home, check out the Learning Center on our website.

Related Articles

Bonus Room Insulation Problems: 6 Things That Cause an Uncomfortable Room Above the Garage

Should I Insulate the Wall Between the Garage and House When Updating Exterior Wall Insulation with Foam?

My Attic is Very Hot! How to Cool Down and Fix a Hot Attic


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About Amanda Ringler

Amanda previously has worked as a breaking news and crime reporter, TV news producer, and editor in Flint and Detroit. Throughout her career as a journalist, she has won several awards from The Society of Professional Journalists - Detroit Chapter and the Michigan Press Association. As part of the RetroFoam of Michigan family, Amanda uses her experience as a journalist to write content that will help educate homeowners on the benefits of foam insulation. When Amanda isn’t writing, she’s spending time with her husband and rescued huskies. She also loves knitting, making art, cooking, and hosting dinner and a movie night for friends and family.