5 Types of Garage Insulation to Consider

Fiberglass Insulation

Best for: Framing

Fiberglass is the most commonly used type of insulation in garages (just as it's the most popular type in homes). It's sold in precut batts and long blankets that fit between wall studs and ceiling joists. You can also get loose-fill fiberglass, which is suitable for blowing into a garage attic space above a finished ceiling.

If the walls and ceiling will remain open (not covered with drywall or plywood), it's a good idea to use paper-faced or encapsulated fiberglass bats that are wrapped in a plastic film. These will give the walls a slightly more finished look, and you won't have the itchy fibers of the insulation exposed and ready to catch dust at all times.

Cellulose Insulation

Best for: Finished garage walls and ceilings

Cellulose is a loose-fill insulation that is growing in popularity. Made primarily from recycled newspapers and treated with a fire retardant, cellulose is usually blown into wall and ceiling cavities with a special blowing machine that also aerates the cellulose and fluffs it up. Blowers can be rented at many tool rental stores, and home centers will sometimes loan you a free one if you buy your cellulose from them.

Because it's loose-fill, cellulose is suitable only for finished garage walls and ceilings. If the garage is already finished (but uninsulated), you can install cellulose by cutting strategic holes in the wall material, spraying the insulation into the cavities between framing members, then patching the holes.

Rigid Foam Insulation

Best for: Thin walls and garage doors

Rigid foam comes in 4-by 8-foot sheets and 1/2-inch to 4-inch thicknesses. The most common materials include expanded polystyrene (similar to Styrofoam), extruded polystyrene, and polyisocyanurate. Rigid foam offers a high R-value per inch of thickness and can be cut to fit almost any space. It's a good choice for thin walls and insulating garage doors.

If you're turning the garage into living space or a full-time workspace and want to insulate the floor, one option is to use rigid foam covered in plywood or other subfloor material.

Spray Foam Insulation

Best for: Garage-to-living-space conversions

Spray foam (beyond the low-expanding canned product) is excellent for both R-value and air sealing. As a high-end material typically used for energy-efficient construction, spray foam may be overkill for most garage projects. But it might make sense if you're converting the garage to a living space.

Garage Door Insulation

Best for: Garage doors

Don't insulate your garage walls and ceiling without insulating the big garage door, too. You can buy insulation kits for standard metal garage doors, or you can cut pieces of rigid foam insulation or Reflectix sheets to fit each door panel/section. Keep in mind that the structural metal ribbing of garage doors is an excellent conductor of heat, and this typically doesn't get insulated. As a result, the overall thermal performance of the door will be well below the rated performance of the insulation itself.

Air sealing is particularly important with garage doors. Create a seal along the sides and top of the door with special garage door trim with an integrated weather-seal strip. Seal along the bottom of the door with a new rubber gasket, or "bottom seal." It's available in different sizes to cover small or large gaps between the door and the garage floor.