Originally Published on: www.spfm.ca
Looking to insulate your garage and trying to decide what type of insulation to use? Find out how spray foam solves problems that traditional insulation can’t and why it’s not just about comfort and energy savings but also contribute to making your home more safe and healthy too!
Garages are one of the key areas in most homes when it comes to insulation and building envelope deficiencies! When your garage is insulated properly, it has the potential to make a huge impact on your energy bills, the comfort in your home, and how many outdoor pollutants are let into your home through these deficiencies.
We have insulated a lot of garages over the years and have found many pre-existing issues in the way they were insulated.
Here are a few key points/areas that need to be considered & addressed when insulating your garage:
Cold Floors Above The Garage:
Many garages either have a full or partial room above them that is usually found to be cold. In our experience, we have found a few sneaky ways that some builders/contractors have tried to mask the issue of cold floors in these rooms at the expense of your energy bills! Find out how in this article.
Why Is The Room Above My Garage Cold? 
These rooms are typically cold because builders/contractors have commonly used traditional fiberglass insulation in the garage ceiling and walls.
Fiberglass is not air-tight as it allows air to travel through it. Fiberglass is the same material used in most furnace filters because of how good it is at trapping all the dust but still allowing large amounts of airflow through it.Take a look at this image, you will see an excellent example of fiberglass doing the same great job it does for your HVAC Unit. The black on the fiberglass batts is not mold, it’s dust, dirt and exhaust fumes that have been “filtered” by the fiberglass insulation as air passes through it and enters into the home. Would you want this insulation to be your only defense against these outdoor pollutants entering your home?
Properly Separating Your Garage From Your Home
We have also found many garages that are not properly separated from the rest of the home within the ceiling cavity that we mentioned above.
The ceiling cavity above the drywall in the garage could be connected to the entire floor of the house. This allows the cold air that leaks into the garage ceiling to flow freely across the entire floor/ceiling cavity of the whole house. This 1ft section between the drywall ceiling and the plywood on the floor above, is commonly found blocked only by a fiberglass batt floating as a divider.
If the cavities in the ceiling are properly blocked off and air sealed so that no air can leak from the garage ceiling cavities into the home ceiling cavities, this one thing alone will make a huge impact on the comfort of the home and its energy bills.
Why Is Spray Foam The Best Insulation For Your Garage Ceiling?
Spray foam adheres to the surface that you spray. It expands and sticks to whatever it touches. It does not allow air passages, leakage and air can’t travel through spray foam insulation and it’s air-barrier and vapor barrier custom installed filling every nook and cranny creating an air-tight, moisture barrier with unmatched insulating performance.
Spray foam insulation is also very versatile, you are able to spray it on all types of surfaces, and even create dried ridgid custom “board-stock” pieces that can be glued or mended together with the spray foam creating strong, completely air-sealed blocking, or false walls.
Let’s say you are in a situation where the fiberglass batt is floating in the cavity without any backing and it can be pushed out of the way (like the drop ceiling pictured previously above in the yellow circle). With spray foam, you could install a piece of cardboard, or house wrap to create a surface and spray over everything connecting it to the wall, as pictured above, making a monolithic continuous insulation blanket separating your garage from your home.
Heating A Dead Space Below The Floor And Above The Garage Insulation:
In many cases, we have seen garages where some builders/contractors have installed the insulation (in the garage ceiling) against the garage drywall. Because it has been installed in the lower portion of the cavity it creates an air space above the insulation, and below the floor in the room above.
Conditioned air is then blown into this space to try to “mask” the cold/hot floor. We have also found cases where there was up to three 6 inch ducts running wide open, blasting conditioned air into the space above the garage ceiling. ultimately leaking most of it into the garage.
This is an extremely inefficient use of your heating and air-conditioning system.
We had a project where we removed the insulation from the ceiling and found 3 x 6” duct runs wide open, blowing conditioned air above the fiberglass, as talked about previously. We sealed and capped off 3 runs blowing hot air into the garage and got the project ready for spray foam to be completed the following day. After a cold night, we came back the next day and our customer had a confused look on their face… “I don’t understand, you removed all of the insulation in the garage ceiling, yet somehow my house was warmer than normal last night?! How does that make sense?”
“Well” we replied “you had 3 hot air registers that were wide open blowing all that hot air into the garage ceiling & we capped them off. Now all of that hot air is actually going into your home where it belongs so it is making your furnace be more efficient.”
Ductwork In The Garage 
Usually, you will find HVAC duct runs in the wall cavities adjoining the garage. When you are insulating the garage ceiling, do not forget the walls could contain ductwork and it should be found, accessed, and insulated. Many times we have found ductwork that is not properly connected or has come apart and the conditioned air isn’t even reaching the room that its connected to in the home. Instead, it is blowing into the garage. Wasting your money and causing comfort issues in the connected room. All while working your furnace harder than it should need to, reducing the life of the furnace and adding unnecessary wear and tear on the unit.
Return/Supply Air HVAC Hidden In The Walls Of Your Garage.
The only thing worse than HVAC ductwork leaking hot air into your garage, is having the “leakage” pull in the air from the garage! You might find it unbelievable but HVAC Supply/Return runs in the walls of the garage. These supply runs could be “leaky” and actually pulling in the polluted air from your garage and distributing it throughout your home! HVAC supply runs should be completely sealed with either a thick coat of mastic or ideally 2lb closed cell spray foam to ensure it’s not sucking in any garage pollutants. If possible even re-routed and kept within the home.
Floor above a garage
This detail shows a garage bonus-room floor framed with open-web floor trusses. To prevent air leaks, it’s important to install caulk at all of the indicated locations. Ideally, the floor assembly won’t include any ducts. If there is no way to avoid installing ductwork in the floor, specify deep floor joists, such as trusses that provide plenty of room under the ducts for insulation, and be sure to include a continuous layer of rigid foam under the joists.” quote finehomebuilding.com
But What If I Want My Garage To Be Warm Like An Insulated Workshop? 
So far we have been talking about insulating the garage ceiling and adjoining walls to protect the conditioned house from the unconditioned garage. But what if you want your garage to be warm? What if you wanted to just insulate your garage door so you didn’t have to worry about all the stuff that we just talked about?
Actually, to make the garage warm, you have to first consider protecting the home from the cold garage and then the garage from outside in addition. Garages can contain exhaust fumes from vehicles & you do not want those fumes to enter your home.
Also, what happens when you open the garage door? Every time you do this it is like opening an entire wall of your home so you will want your garage insulated to protect your home from when the door is open.
Garage Door Insulation
Spray foam is great for insulating garage doors because it can be sprayed at a thickness that is as thin as 1 inch, and if the applicator is skilled, you can get a very clean smooth consistent foam insulation blanket on the garage door.
Because spray foam insulation is rigid, once it is sprayed, your garage door is pretty solid. If you have the style of garage door that has panels that bend it is pretty easy to cut the spray foam with a sharp knife along the seams in a V shape which allows the garage door to open and still get a great seal.
Insulating your garage provides more than just increased comfort and efficiency. As Mike Holmes says, “A properly insulated garage is a safety must” and you cannot always assume the builder has taken these important unseen “details” behind the drywall into consideration during the build.
Look at insulating your garage as an opportunity to take a look at what is hidden behind that drywall, investigate any potential issues and do it right and solve many problems instead of just one!
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