If your plan is to heat the space of your garage, insulating makes the most sense. You can use the same materials for insulation that you use around the house for your garage, but depending if your garage is finished or not, some insulation types are better than others.
The garage door may also need insulation, although there are different insulation requirements than walls or ceilings.
The main point of insulation is keeping in the heat if you are thinking of adding heat to your garage space. If you aren’t, then insulation may not be worth it. Insulation does not add warmth, despite the misconception. Insulation slows down the transfer of heat through an insulated barrier, such as the wall or floor.
It is said an unheated garage attached to the home may benefit from insulated walls and ceilings of the garage, as it can act as an additional thermal buffer between the exterior of the house and the outdoors.
The energy-efficiency mandates don’t require this in any states however. This minimal improvement will least likely reduce costs of extensive insulation due to the small difference in the energy transfer. If the walls are shared, insulation can provide maximum value.
Air-sealing with insulation can be extremely valuable. Garages usually have air gaps to the outdoors, making them not airtight friendly. To have the highest R-value possible, insulate the walls, door and ceiling of the garage. You will be wasting a lot of heat however if the air gaps are not filled.
Before insulating, use a can of low-expanding spray foam and seal cracks and gaps that let in the daylight. Alongside the bottom of the garage, make sure the weather-stripping is intact, along with the window and door frames sealed against drafts.
The most commonly type of insulation used in garages is fiberglass, which is also popular in homes. Sold in pre-cut batts and long blankets that fit between ceiling joists and wall studs. Loose-fill fiberglass is also an option, which is common in garage attic spaces above a finished ceiling.
Paper-faced or encapsulated fiberglass bats wrapped in a plastic film are a good idea if the walls and ceiling remain open, meaning they are not covered with drywall or plywood. Doing this will have the fibers tucked in, not exposed to dust that it usually catches and a finished look.
A loose-fill type of insulation that is growing in popularity, called cellulose. It’s made from recycled newspapers, treated with a fire inhibitor and blown into a wall and ceiling cavities with a specific blowing machine that ventilates and fluffs it up. The blowers can either be rented or loaned to you by your local hardware store.
Cellulose is only suitable for finished garage walls and ceilings however, because it’s loose-filled. In a finished uninsulated garage, install cellulose by cutting strategic holes in the wall material, spray into the cavities between frame members, then patch the holes.
Rigid foam is good if you’re turning the garage into a living space or a workspace and want insulation on the floor, by using the rigid foam covered in plywood or other subfloor material. Rigid foam produces a high R-value per inch of thickness and can fit in any space when cut properly.
It comes in 4 by 8 sheets and thickness of ½ inch to 4 inches. Expanded polystyrene, which is similar to Styrofoam, extruded polystyrene and polyisocyanurate are the most common materials. Always check the fire rating on rigid foam, as some are not fire-resistant and not fit for exposed applications.
If you want a combination of R-value and air sealing, spray foam is the right one for you. It’s a high-end material used for energy-efficient construction.
Some may consider spray foam an overkill for most garage projects, but is the best option is you want to convert the garage to a living space.
If you’re going to insulate your garage walls and ceiling, you must insulate the garage door too. Insulation kits are available for metal garage doors. Cutting pieces of rigid foam to fit each door section is also an option. The structural metal ribbing of garage doors conducts heat and doesn’t get insulated for the most part. The performance of the overall thermal conduction will be below the insulation itself because of this.
Because of it’s importance, air-sealing garage doors are a must. Along the sides and top of the door, create a seal with a special garage door trim with an embedded weather-seal strip. The bottom of the door should be sealed with a new rubber gasket.
Different sizes are available to cover large and small gaps between the floor and the garage door.