How To Insulate A Garage Ceiling Rafters

Chloe Meltzer
by Chloe Meltzer

Having a freezing cold garage in the winter is never fun. Not only is it horrible to go into your garage when it is cold, but the cold can also damage your vehicles. Insulating your garage ceiling rafters is a great option. Insulating the ceiling rafters of your garage is actually the most essential part. This is because heat rises and can leave through the roof. Always make sure the top of the garage is protected if you want to keep in essential heat.

Clear the area around the rafters and fill the cracks 50% with expanding foam. Let the foam harden for 8 hours and staple fiberglass installation to the sides of your studs. Remove excess insulation with a utility knife and cover the insulation with drywall.

This article has all the information you need to do a complete insulation installation for your garage ceiling rafters. We also explain the R-values and provide additional tips so you can do a job as good as the pros!

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Supplies You Will Need

  • Fiberglass insulation

    Although there are many types of insulation, in order to fully insulate your garage ceiling rafters, you will first need to pick a material to use. Fiberglass insulation will be the easiest to install yourself; otherwise, you may need to go with a professional.

  • Garage door insulation kit

    These can be used for your ceiling rafters rather than your garage door, as the name states.

  • Expanding foam

    This will be helpful if you have any gaps or cracks where you plan to insulate. This keeps the outside cold from getting inside. There is both a low-expanding and high-expanding form. You should purchase this based on the size of the spaces in the wall.

  • Drywall
  • Gloves, long-sleeves, and pants

    Fiberglass can irritate your skin, so protect yourself with long sleeves, pants, and gloves.

Tools You Will Need

  • Utility knife

    Your knife must be sharp to cut the insulation.

  • Wood

    Wood pieces should be pre-cut. They will be used to measure the insulation while cutting

  • Staple gun and staples

    These keep the insulation in place.

Tips For Insulating Your Garage Ceiling

  • Use thicker R-40 insulation. If you have ever insulated the walls of your garage, it is very similar to doing so for the ceiling. The main difference is you should use thicker R-40 insulation.
  • Measure and pre-cut. To stay safe, be sure to measure the height and width between the framing in the ceiling and pre-cut the pieces you’ll need. This will make things go smoother while you are on the ladder.

What Is Fiberglass Insulation?

Fiberglass insulation is made of very small fine glass fibers. This has a paper face on top of it and often looks like cotton candy. It is typically sold in rolls or bags.

Fiberglass insulation comes in different R-values. R-Value measures how well specific insulation can resist heat, which also tells you how well it insulates.

R-Value Explained

For homes built before the 1990s, it was typically to build with 2×4 studs. For homes built with 2×4 studs, to insulate the walls, you would use R-13 insulation. Newer homes are more often built with 2×6 studs. This means they will require R-21 insulation.

Despite all of this, you will need to use R-40 thick insulation when working to insulate your ceiling rafters.

Instructions To Install Insulation In Your Garage

Step 1: Clear The Area

Typically this step is more critical if you are insulating garage walls, but if there is any drywall where you plan to insulate, remove it. You should also make sure to clean any dirt or mold. It should be very clean before you proceed with sealing any cracks or gaps. This is because the dirt can affect the sealant.

Not to mention, if you have any mold, this will eventually grow into a larger problem, and you may have to replace your entire roof eventually. Therefore, it’s better to deal with now instead of later.

Step 2: Look For Gaps And Cracks

If there are any gaps or cracks, you must seal them. You can do this with your expanding foam. Before using it, make sure to shake it for about one minute intensely. Then attach the straw to the can, and hold it upside down while you spray the gaps or cracks.

Be aware that expanding foam will continue to expand after spraying, so be sure only to fill any gaps or cracks about 50%. After anywhere from five to twenty minutes, it should be finished expanding. After eight hours, it will be hard and fully “dry.” Wait for it to dry before you go on to the next step.

Step 3: Install The Insulation

As we recommended before, use fiberglass insulation for the best DIY result. To begin the installation, staple the paper face of the insulation to the side of the stud. Make sure you avoid the face of the stud.

This needs to be exposed in order to put drywall on top of the insulation. The last thing you want is exposed insulation, so drywall is going to be necessary.

Properly Cutting The Insulation

To properly cut the insulation, you can use a piece of wood. Choose a piece of wood that is the same size as what you need to cut your insulation to. Put it on top of the insulation, and use it as a guide to cut it to the right size.

Use your utility knife to cut the insulation, so it fits properly, then tuck it down to staple it. Make sure the insulation is stapled fully down to the side of the stud.

Step 4: Cover With Drywall

At this point, you are almost done. Now you will need to cover the Insulation with drywall. Be sure to screw and glue drywall to the stud.

NOTE: Make sure you cut off or tuck in any paper of the insulation. This is a fire hazard.

Should I Insulate My Garage Door As Well?

While insulating your garage ceiling was easy, a door is much more involved and challenging. Instead of taking the time to insulate your garage door, it’s a wiser decision to purchase a pre-insulated garage door to bypass any hassle. However, if you cannot afford one (They’re pretty expensive), then you can buy a garage door insulation kit.

The process is similar to insulating your ceiling; however, your garage door will be adding weight to the insulation. Due to the weight of the tension on the springs, your door may not stay closed properly.

How Much Will It Cost To Insulate My Garage?

It will cost you between $0.50 to $1.25 per square foot to insulate your garage. So, if you’re insulating a two-car garage, you can do this for $345 to $850. It depends on how much of it you are insulating, as well as the insulation materials that you purchase. Also, don’t forget to account for any tools you need to buy or rent as well.

If you decided to hire a professional to do this, then the cost will be quite a bit more. You would be looking at $345 to $850 plus the cost of labor. For labor, you would be paying between $45 and $150 per hour depending on who you hire, and the company that you go through. However, this is such an easy project to do on your own. We advise you to attempt this on your own before paying the money to hire someone.

Related Questions

Do I need to heat my insulated garage?

If you are looking to use your garage as a place to spend time during the winter, insulation might not be enough. This depends on where you live and how cold it ends up getting. You may end up wanting a heating source. This could be a space heater if you choose.

What type of insulation should I use?

You can use a few different types of insulation, but fiberglass insulation would be the best. This type of insulation is easy to install without the help of a professional. It is also great to use between framing and can be used in all areas of your garage.

How much insulation do I need?

To find out how much insulation you will need to start by measuring the linear feet around the entire room. Take this number and multiply it by the height of the room. This will be your square footage. Always buy an extra unit of insulation and simply return it if you do not need it.

Do You Need Insulation Installers?

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Our Take On It

Insulating the rafters of your garage is an easy task that anyone can do. However, you will need to make sure you measure accurately and take your time doing so. On the other hand, if you are looking to insulate the entire garage, it may be a good idea to purchase a garage door that is already insulated. Other than that, this is an easy project that is perfect for beginning DIYers. Just make sure you have the tools for the job beforehand!

Chloe Meltzer
Chloe Meltzer

Real estate agent and copywriter, originally from California. Chloe brings her real estate expertise into her writing to create effective and helpful home guides for you! When not writing or selling homes, she spends her time as a digital nomad traveling the world.

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