Garage Insulation 101: Best Types and Techniques

Garage insulation prevents energy loss in temperature-controlled garages. In most cases, you can use the same type of insulation in the garage as you would in your house. The biggest difference in insulation techniques is the overhead garage door and the floor.

Garage Insulation 101

Why Insulate Your Garage

Heated or air-conditioned garages need insulation to minimize heat loss or heat gain. Money spent on heating or cooling an uninsulated garage is better spent on insulating the garage. Insulation also improves the soundproofing qualities of the building, keeping noise out and sound in.

Many garages are used for more than–or instead of–storage and/or vehicle parking. These can include a workshop, hobby space, man cave, band practice room, or home theater/entertainment space–among others. All of which are more enjoyable in a warm or cool area.

When Not to Insulate a Garage

If the garage is unheated, insulating against heat loss is a waste of time and money. It is more effective to ensure that the garage is moisture-proof, rodent-proof, and pest-proof.

Types of Garage Insulation

The types of garage insulation include the following products.

1. Batt or Roll Insulation

Often called blanket insulation, batts are useful for insulating walls and ceilings. Types of batt insulation include:

  • Fiberglass Insulation. Most common and least expensive.
  • Mineral Wool Insulation. Also best for soundproofing
  • Denim Insulation. Most ecologically friendly but difficult to find and expensive.
  • Cellulose Batts. Expensive and difficult to find.

2. Cellulose or Fiberglass Loose-Fill Insulation

Cellulose insulation is a versatile option for a garage. Installers can blow it into the attic or into walls with netting to keep it in place until the drywall is installed. You can also blow cellulose wet to stick to walls until covered. If your walls are finished, you can add cellulose by drilling small holes into the drywall and blowing it in.

Cellulose is made from recycled newspapers with added borax to make it fire-resistant. The borax also repels insects and rodents.

Fiberglass loose-fill insulation can be blown into attics but is a poor option for walls–finished or unfinished.

3. Spray Foam Insulation

Spray foam insulation provides R-5 per inch. It expands to fill the stud cavities, cracks, and voids around electrical boxes and wires, plumbing pipes, nails, and framing. Spray foam installation is best left to professional installers. 

4. Rigid Foam Board Insulation

Rigid foam board insulation can provide up to R-6.5 per inch. Popular options include expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate (ISO)

Rigid foam board insulation goes between studs of the wall and between rafters on vaulted or sloped ceilings. You can also attach it to the face of studs and rafters unless retaining as much floor area as possible is essential.

Rigid foam is useful for non-standard framing, such as 2 x 2 and 2 x 3. XPS is effective for insulating the garage floor on the inside. (It’s also the best choice for insulating under a concrete floor if one needs to be poured.)

What to Do Before Insulating Your Garage

Potential problems are easier to deal with before installing insulation and drywall in your garage.

Repair or Replace Windows and Doors

Many garages were–and are–built on the cheap. That includes second or third-hand single-glazed windows and hollow core doors. Insulating a garage to R-12 or better without addressing painted-shut R-1.0 windows defeats the purpose.

Add energy-efficient windows if possible. It is much easier to modify openings before the insulation and drywall are installed.

Seal Gaps and Penetrations

Gaps in exterior sheathing and large wall penetrations are easier to see and fix from the inside. Seal smaller cracks with acoustic caulking – it never dries and will expand and contract while adhering to the surrounding material.

For larger holes, use low-expansion spray foam. If the hole is big enough to be a rodent pathway into the garage, stuff steel wool into the opening–then foam it. Steel wool is a great pest deterrent.

Repair Water Leaks

Find and repair any water leaks–roof, walls, or around windows and doors. If the roof is leaking, have a professional roofer do the repairs.

If possible, seal all leaks from the outside. Water pressure and wind pressure will only force sealant deeper into the gaps and cracks. Interior sealant fails more often, and water can find an easier pathway inside.

Garage Areas to Insulate

Insulating a garage can involve one or all of the following areas: the door, walls, ceiling, floor, and windows. The choices you make depend on garage use, how much insulation, cost, and time.

If the garage is to become a living area or a tiny house, local residential building codes may apply. Inquire before starting to avoid unnecessary costs and effort. Insulation R-values vary by climate zone.

How to Insulate a Garage Door

The garage door is the largest opening in the building and usually has the worst insulation. Newer doors often feature expanded polystyrene sandwiched between aluminum or steel panels. R-values range from R-8 to R-32. Old steel doors have an R-value of zero.

Garage door insulation kits are rated around R-8. These DIY kits are readily available from home improvement outlets or online. Many DIYers insulate overhead doors by cutting and installing rigid foam boards. The foam is attached with self-impaling clips and/or foamboard glue.

Most garage door insulation does not cover structural steel components or hinges. A quick, easy, and inexpensive option is stringing a line close to the door and hanging moving blankets. The blankets keep the heat in or out as required and absorb sound. You can remove and replace them as required.

Also, replace the weatherstrip. Garage door weatherstripping is notorious for poor adjustment, rips and tears, and becoming hard with age. Some old doors only used an L-shaped steel top piece. Replace sides, top, and bottom, and use a large door bottom seal that will accommodate uneven floors.

Garage Wall Insulation

You can insulate garage walls with any of the batt products mentioned above or with rigid foam boards between the studs or on the face of the studs before drywall installation. Cellulose can be wet sprayed onto the sheathing or installed dry behind netting. Professional installers can spray it into stud cavities without removing the drywall. 

Spray foam is another option that professionals can spray into the stud cavities. It has great insulation value but is poor at soundproofing. 

Garage Ceiling Insulation

You can insulate garage ceilings with batts, loose-fill cellulose, or loose-fill fiberglass. These are fairly simple DIY projects. You can rent blowing machines from building supply stores – sometimes, the machine is rent-free if you buy the insulation from the store, but the ceiling drywall has to be installed before insulating.

Blown-in insulation provides better insulation and R-values in comparison to batts. The material fills all the cracks and gaps. 

Insulate vaulted garage ceilings with rigid foam boards between the rafters against the underside of the roof deck. Seal any gaps with acoustic caulking or spray foam in a can. Since up to 30% of heat can escape through the roof, R-20 or better is advisable.

Garage Floor Insulation

Insulate your garage floors in one of two ways:

  • Batts. Lay 6 mil poly over the concrete. Install 2 x 4 sleepers on edge 16” on center. Install batt insulation. Cover with ¾” plywood and finish as desired.
  • Rigid Foam. Cover the floor with 2” XPS rigid foam. Cover the foam with ¾” plywood laid perpendicular to the foam so joints do not line up. (You may want to attach the plywood to the concrete using a powder-actuated nailer, but it is usually not necessary.) Add another layer of ¾” plywood perpendicular to the first. Screw it to the first layer and finish as desired.

Parking a vehicle on the foam floor will not affect it, but the batt floor may require another layer of plywood or sleepers at 12” on center to accommodate the weight.

Courtesy: YouTube > Hilti North America – Powder-actuated nailer

Window and Door Insulation

Ensure the gaps between window and door frames and the wall framing are well insulated. The preferred method is to spray about one inch of low expansion foam against the backsides of the exterior brick mold, then fill the rest of the gap with fiberglass. Do not pack the fiberglass tight. The tighter it is–the lower the R-value.