Garage Insulation 101

Garage insulation is the same type of insulation used in houses. Quite often it is used in the same locations in the same ways. There are a few differences such as the overhead garage door and the floor.

Garage Insulation 101

Why Insulate Your Garage

Heated or air conditioned garages should always be insulated 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 greatly improves the soundproofing qualities of the building. Keeps 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.

Types of Garage Insulation

The types of insulation most often used in garages include the following products.

1. Batt or Roll Insulation

Often called blanket insulation, batts are most often used to insulate walls and ceilings. Types of batt insulation include:

  • Fiberglass Insulation. Most common. Least expensive.
  • Mineral Wool Insulation. Also best for soundproofing
  • Denim Insulation. Most ecologically friendly. Difficult to find. Pricey.
  • Cellulose Batts. Expensive. Difficult to find.

2. Cellulose or Fiberglass Loose-Fill Insulation

Cellulose insulation is a versatile option for a garage. It can be blown into the attic. It can be blown into walls with netting to keep it in place until drywall is installed. Cellulose can also be blown wet to stick to walls until covered. It can be blown into finished walls by drilling small holes into the drywall.

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. It 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 usually best left to professional installers. Wall insulation can also be a DIY spray foam project for some do-it-yourselfers.

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). It provides up to R-6.5 per inch.

Rigid foam board insulation can be installed between studs of the wall and between rafters on vaulted or sloped ceilings. It can also be attached to the face of studs and rafters unless retaining as much floor area as possible is essential.

Rigid foam is very 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 is also the best choice for insulating under a concrete floor if one needs to be poured.)

Garage Door Insulation

Installing a garage door insulation kit can add R-8 to your door. The kits are reflective foil insulation and contain everything necessary to complete the installation. Other options include attaching rigid foam panels or bubble wrap insulation.

Garage Areas to Insulate

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

If the garage is to become an extension of the living area of the home 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.

Resolve Potential Problems Before Insulating

Most potential problems are easier to deal with before insulation and drywall are installed. Better access. Easier to see. Usually less expensive.

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.

Replace them if you can. It is much easier to modify openings before the insulation and drywall are installed.

Seal Gaps and Penetrations

Gaps in exterior sheathing and excessively large holes made for 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, it may be time to 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 Door Insulation

The garage door is the largest opening in the building and usually has the worst insulation. Newer doors are often sandwich panels with 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. They can be removed and replaced as required.

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. Make sure to use a large door bottom seal that will accommodate uneven floors.

Wall Insulation

Garage walls can be insulated with any of the batt products mentioned above. They can also be insulated with rigid foam boards between the studs or on the face of the studs before drywall is installed. Cellulose can be wet sprayed onto the sheathing or installed dry behind netting. It can also be sprayed into stud cavities without removing the drywall. Installing cellulose in walls usually requires contractors with the equipment and experience.

Spray foam can be sprayed into the stud cavities. It has great insulation value but is poor at soundproofing. Spray foam should be professionally installed. Contractor-installed insulation will increase costs. It can also be installed by experienced DIYers.

Ceiling Insulation

Garage ceilings can be insulated 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 will be rent-free if you buy the insulation from the store. The ceiling drywall has to be installed before insulating.

Blown-in insulation provides better insulation and R-values. The material fills all the cracks and gaps. Batts can be difficult to fit properly.

Vaulted garage ceilings can be insulated with rigid foam boards installed between the rafters against the underside of the roof deck. Seal any gaps with acoustic caulking or spray foam in a can. Up to 30% of heat can escape through the roof. R-20 or better is advisable.

Garage Floor Insulation

Garage floors can be insulated efficiently in 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. 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

Make sure that 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.

When Not to Insulate a Garage

An insulated garage provides many benefits including increased sale value but it may be an expense not worth incurring. Many garages are only used for storage or parking vehicles. If the garage is unheated, insulating against heat loss can be a waste of time and money. It is more effective to ensure that the garage is moisture proof, rodent-proof, and pest proof.

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Written by Murat

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