Insulating a garage requires air sealing the wall cavities and correctly applying the insulation, according to How To Home Insulation. To air seal the walls, look for obvious holes, gaps or cracks. Fill these in with several squirts of Great Stuff and silicone caulk. Insulation for walls attached to a home should be installed backwards, while insulation for non-attached walls should be installed with the paper-side facing outward.
When air sealing, it is important to focus attention on the bottom walls that are attached to a living space, because fumes, such as carbon monoxide, often leak into the home through the base of the wall. The most effective way to prevent this type of leak is to run a bead of silicone caulk along the bottom of the wall, between the wood and concrete. Then smooth out the caulk hand: This forces the caulk into the crack so the seal is complete. Use a can of Great Stuff to seal the perimeter of the 2 X 4's, where they touch the garage walls. Remember, the insulation is installed with the fuzzy part facing outward and the paper-side facing inward for attached walls. Most garages are framed with 2 X 4's, which matches 15" R 13 insulation.