How to Insulate a Garage

Tips for Insulating your Garage

By Mark J. Donovan




Many garages are left uninsulated and that may be just fine if you have no other intentions for your garage other than storing automobiles. However if you expect to be in your garage often, you may want to consider insulating your garage. By insulating your garage you can create a more comfortable environment for a workshop or for even creating additional living space.

When insulating your garage walls always wear full length clothing, a mask, and a pair of goggles, as fiberglass insulation can be irritating to your eyes, throat and skin. Also it is important to keep in mind when insulating a garage to do a neat job, such that there are no gaps in the insulation.

Much of your efforts and money spent on insulation will be wasted if your finished insulated garage is peppered with small un-insulated gaps.

Insulating Garage Walls

Insulating a garage begins by installing rolled or batt insulation in the garage exterior walls. Depending upon the framing used in the construction of your garage you should use either R-19 or R-11 insulation. If the garage walls were constructed with 2x6s you should use R-19 insulation. If they were constructed with 2x4s then use R-11 insulation. You can use either faced insulation or unfaced insulation.

However, if you use an unfaced insulation you will need to add a plastic vapor barrier over the garage walls after installing the insulation. If you used faced insulation the paper side should face the interior of the garage.

Cut the rolled or batt insulation into the appropriate lengths to fill the bays between the garage wall studs. Use a utility knife and a length of 2×4 to cut the insulation.

If you are using a faced insulation staple the paper face tabs to the wall studs. Apply staples every 12” or so along the height of the bay.

Insulating walls between garage and main house to keep the house warmer.

Next install pieces of insulation in-between window frames and wall studs and above and below the window and door frames. Use a screwdriver or a putty knife to work the insulation into the narrow spaces. Alternatively you can use a spray foam insulation that you can find at any home improvement center. These types of insulation work great and can typically do a better job getting into small narrow spaces.

Likewise make sure insulation is fastened snuggly around all electrical boxes.

Insulating Garage Ceiling / Attic Area

Next install insulation between the garage roof rafters, to insulate the garage ceiling. You should use a minimum of R-30 insulation. However before installing the insulation it is best to first install furring strips perpendicular to the roof rafters. The furring strips are 1”x3” lengths of lumber that are nailed on 16” centers perpendicular to the roof rafters. The furring strips will hold the attic insulation in place and allow drywall to be attached to the garage ceiling. Again, if you are using a faced insulation on the garage ceiling make sure the paper faces towards the interior of the garage.

Installing a Vapor Barrier

If you installed unfaced insulation it is imperative to install a vapor barrier. The vapor barrier slows the transfer of moisture from the warm moist room to the cold drier outside air.

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By slowing this moisture transfer rate, condensation is prevented from occurring inside the garage walls/ceiling. By preventing condensation the risk of rot, mold and mildew are reduced. To install a vapor barrier simply install polyethylene plastic over the insulation. Staple the plastic to the wall studs and/or furring strips. Make sure you overlap sections of plastic by at least 6 inches, or one additional bay.


For help on building a home addition, see HomeAdditionPlus.com’s Home Addition Bid Sheets. Our Home Addition Bid Sheets provide you with the knowledge and information on how to plan a home addition project, and what to look for when hiring contractors. They also include detailed cost breakdown tables and spreadsheets for estimating your own new home addition building costs.

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