The Pros and Cons of Each Type of Garage Insulation
By Jacquelyn Nause
Garages are often uninsulated, but when adding heat for a workshop or finished apartment, insulating a garage is necessary. Insulation materials are the same as for other areas of the house, but some are better suited for garages. Let’s look at each.
Garage Insulation Basics
Use insulation to minimize heat loss through barriers such as walls, ceilings and floors. Garages are not usually insulated except in barriers that are shared with the main house, such as a connecting wall or ceiling that borders a livable area above or below the garage.
When adding insulation to temperature-control a garage, it’s also important to air-seal any gaps to the outside. Go around the garage with a can of spray foam and seal any gaps or cracks that allow air or light from outside.
Garage insulation needs to be fire-rated by law, due to the likelihood of combustible liquids being stored there. Insulation comes in batt or blanket sheets, or in loose-fill formats that can be sprayed into spaces with a special machine.
Fiberglass is currently the most common insulation material and is sold in pre-cut batts and blankets. Loose-fill fiberglass is also available and is suitable as blown-in insulation for attic spaces above a finished ceiling. Fiberglass batts are convenient material for insulation because they are highly flexible and able to be wrapped around pipes and hand-cut to fit nearly any space.
Ensure proper installation, as batting can be pushed into awkward spaces and lose effectiveness as a thermal barrier. For example, walls are usually covered with plywood or drywall, but if the walls or ceilings will remain open, use paper or plastic-encapsulated batts to keep the fiberglass fibers contained. The convenient rolls of fiberglass batting are easy to transport and install; however, the batting can lose effectiveness over time as the fibers degrade and compress.
With enclosed walls, the easiest and most cost-effective insulation option is blow-in cellulose. Cellulose is gaining popularity as an insulation material and is derived from recycled paper waste with added fire retardant. It can fit into irregularly shaped areas, making it great for awkward spaces and areas with wires or ductwork.
Because the walls are finished prior to installation, holes are drilled into the wall material to allow insertion of the blower nozzle. Walls are then patched up and painted. In attics, you can blow cellulose parallel to joists or lay it on top of existing insulation.
Rigid Foam Boards
Rigid foam boards come in various thicknesses and sheet sizes and can be hand cut to fit nearly any space. Made of dense foam, rigid boards offer a higher R-value per inch relative to other types of insulation. Proper installation requires the prevention of any gaps, which can be filled with a spray foam.
Made of polystyrene and polyurethane, the two main issues with rigid foam are its cost and environmental impact. The panels emit toxic smoke when burned and, while they can be recycled, facilities are hard to come by and the material ends up polluting landfills and waterways.
Spray Foam Insulation
Open-cell and closed-cell polyurethane spray foam are more expensive than batt insulation, and also have higher R-values. Spray foam forms a tight air barrier and is an effective sealant but does not prevent water vapor from passing through. These spray foams also release VOCs—volatile organic compounds—during application, so you will need to wait up to three days to re-enter. Once the foam is sprayed into framing cavities and allowed to dry, the excess can be cut away leaving a flat surface.
The best insulation for garage walls and attics depends on how you plan to use the space, if it is finished or unfinished as well as the recommended R-vales for the area you want to insulate. Insulating garage doors or floors requires different materials than walls or ductwork, so be sure to understand how the room will be finished and used before moving ahead.
Jacquelyn Nause is a contributing writer with specialties in real estate, parenting and wellness. She enjoys traveling with her husband, being a doting mother to her two incredible kids and enjoying the beautiful Pacific Northwest playground.