Insulating your garage is a project that can bring two good things to your life, cost savings and comfort. If your garage is attached to your house, the common walls are probably already insulated as required by code, but the other walls often aren't. So, insulating the other walls in your garage will save you some money on your home heating bills. The comfort part comes in two ways. Insulation will make your garage more comfortable, warmer in the winter and cooler in the summer, and since insulation also blocks sound, any project noises coming from inside the garage will be minimized and that's a comfortable bonus to anyone outside the garage.
Adding insulation to open garage walls
Perhaps the easiest way to add insulation to open garage walls is to install fiberglass bats between the studs. Bats are manufactured in widths of either 13" (to fit in between studs 16" on center) or 21" (for studs 24" on center). They are also commonly available in two thicknesses', 3 ½" (to fit into 2 x 4 framing) or 5 ½" (for 2 x 6 studs).
If you choose paper backed bats they are simply placed between the studs from the floor up to the ceiling with the paper side facing out then stapled in place. The paper backing provides a vapor barrier to help prevent moisture from moving between the warmer interior of the garage and the colder exterior (or vice versa in the summer).
Bats without paper backing can also be used. With no paper backing, they are held in place between the studs by friction, but they should be covered with an unbroken sheet of 6-mil plastic sheet stapled over top of the entire wall to provide the vapor barrier.
Insulating garage walls already drywalled
You may think that because your exterior walls are drywalled they are already insulated (and they may well be). However, unless you know who built the garage, you're safer to check for yourself - there isn't always insulation behind a sheet of drywall.
You might be able to see some indications of insulation at the bottom or top of the wall, but if you want to be really sure, poke a hole in the wall and use your fingers to reach in and feel or use a flashlight and look inside.
If there is no insulation you don't need to remove the drywall to add some. Blown spray foam insulation can be installed through holes in the top of the drywall and between the studs. The foam will run down the cavity and expand to fill in behind the drywall and providing high R-value insulation as well as totally blocking air movement once it has cured.
Slow curing foam insulation is designed to flow over obstructions before it sets up so it's ideal for an application like this where it needs to move in behind the drywall before expanding and curing.
Don't forget the doors
In an effort to minimize costs builders commonly provide uninsulated garage doors. Many garage door manufacturers make custom insulation panels for their garage doors, designed to fit right onto an overhead door.
Murray Anderson is an experienced freelance writer over 500 articles published on the web as well as in print magazines and newspapers in both the United States and Canada. He writes on a wide range of topics and is a regular contributor to DoItYourself.com. He can be contacted at firstname.lastname@example.org.