Tips for Ensuring Garage Insulation Is Up to Par and Doing Its Job

Published on: December 4, 2014
Installing insulation | AC Southeast®

The expense and effort to air-seal and insulate your living spaces should be matched by attention to garage insulation, as well. In most residential construction, garages are typically not built to the same careful standards of energy efficiency and air-tightness as the houses they’re attached to. A frigid, uninsulated garage in winter acts as a heat sink that draws heat out of adjacent rooms in the home, increasing heating expenses; in the summer, the garage can be a reservoir of 24/7 heat energy that seeps into the home through air leaks. A garage is also a repository of fumes from paint and gasoline that can contaminate indoor air quality and even deadly carbon monoxide gas. Noise pollution is also a problem in a house with an attached garage. Garage insulation and air sealing help mitigate all these problems.

The goal of proper garage insulation is not to make your garage a conditioned zone like your living room or bedroom. It’s to make it a temperate zone, moderately resistant to acute temperatures. You may not want to move into your garage after it’s properly insulated, but you’ll feel better about being attached to it.


The function of insulation is to slow the conduction or radiation of heat through solid surfaces like a wall or a ceiling. How well a specific material fulfills this role is indicated by its R-value. “R” means heat resistance and the higher the numeral that follows it, the more efficiently the specific insulation holds back the transfer of heat. Insulation has a base R-value that indicates its estimated resistance per inch. To figure the total installed R-value—usually the way it’s expressed in consumer recommendations and manufacturers specs—multiply the depth of the installed installation in inches times the base R-value.

Types of Insulation

Materials used to insulate the garage are for the most part no different from those used for insulating living spaces.

Fiberglass batts are insulation blankets that are pre-cut to specific standard widths and lengths for easy installation and sold in rolls. Batts will normally fit without alteration into the 14.5-inch space between studs in the wall or between the attic joists. This makes a fiberglass batt installation generally the easiest type of garage insulation project for the typical DIY-er. A standard fiberglass batt has a base R-value of around 3.2 per inch.

Cellulose loose fill garage insulation closely resembles snowdrifts when installed in the attic. It’s actually composed of fragments of pulverized paper and cloth that have been treated with a special chemical to make them fire-resistant. Unlike fiberglass batts, cellulose requires special equipment for installation since it’s blown into the attic or finished walls by air pressure through large-diameter hoses. Also, since it’s a loose-fill product, it can’t be installed into the walls of the typical unfinished garage without closing the walls first with drywall or other covering. However, a professional insulation crew can blow it into an attic easily. At 3.8 per inch, cellulose provides a higher R-value than fiberglass.

Expanded polystyrene (EPS) rigid foam board is a common product used to insulate walls and floors. In a garage insulation application, it’s usually the material of choice for insulating the inside of the garage door. EPS cuts easily and is very light weight, so installation presents no major challenge to most do-it-yourselfers. To simplify insulation of a garage door, kits are available that provide all materials and tools in a single package for standard size garage doors. Most EPS board used in homes has an R-value of 4.8 per inch.

Insulating Walls

Before insulating to retard heat transfer, seal direct air leaks that carry air into or out of the garage. Fill visible gaps or cracks in the plywood between the studs of the unfinished wall with silicone caulking. On the wall shared with the home, pay attention to any electrical switch boxes or outlet boxes that protrude the wall. Caulk around the edges of the back of these boxes and also along the contact point between the lower 2 x 4 framing member and the concrete foundation. Using polyurethane spray foam, apply a sealing bead where the wall studs contact the plywood that forms the interior wall of the home or the garage’s exterior wall.

Fiberglass insulation releases fibers that may irritate and be hazardous to breathe, so don protective eyewear, a dust mask and gloves. Per the Department of Energy insulation climate zone map, the southeastern part of the country requires wall insulation ranging from R13 to R15. This makes common R15 fiberglass batts a perfect fit for our climate. Standard width 15-inch batts fit without alteration into most wall voids.

Measure the height of the wall void between the studs and cut a length of batt to fit the height with a razor knife. Fluff the batt like a pillow, then push it gently between the studs and into the wall void. If you’re installing insulation in the wall shared with the home, the paper side of the batt should face toward the plywood wall. If you’re insulating one of the garage’s exterior walls, face the paper side toward you. Once the batts are pressed into the wall space, staple the paper flaps of the batts to the 2 x 4 stud on each side to secure them.

Insulating the Attic of the Garage

Because garage insulation has no effect on air leaks—except to conceal them and make them that much harder to pinpoint later—seal air leaks first, then insulate. Use silicone caulking or polyurethane spray foam in a can. Seal around any points where plumbing pipes or vent stacks pass through the ceiling into the attic. Also take note of recessed lights in the garage ceiling that protrude into the attic and seal around the perimeter of those, as well.

The gap between attic joists can be filled with standard 15-inch fiberglass batts that insert snugly into the space. Here in the southeast region, the D.O.E. map specifies fiberglass attic insulation ranging from R30 to R60, a depth of 10 to 18 inches. Fiberglass batts with this total R value can be installed using roughly the same procedure to measure, cut and place the batts. In the attic, however, make sure the paper side of the batt faces down toward the garage.

Though a commercial insulation installer with the right equipment is the best choice for installing loose-fill cellulose, the preparation work including sealing air leaks is very doable for the do-it-yourselfer. In our climate zone, install cellulose loose-fill in the attic to a minimum depth of 8 inches.

Insulating and Weatherstripping the Garage Door

Expanded polystyrene (EPS) rigid foam board is supplied in kits to insulate standard sized doors. Depending on the kit purchased, the process will require cutting the boards with a razor knife to the dimensions of the garage door panels, then affixing the boards to the door with double-sided tape or some other retaining method.

The opening surrounding the perimeter of a garage door is a gaping pathway for cold or hot outdoor air that turns your garage into either a frigid or overheated unconditioned zone. Standard lengths of PVC garage door weatherstripping can be mounted along the moulding that surrounds the door, positioned at the proper distance to effectively seal this large breach. Screws or nails driven through holes pre-drilled in the weatherstripping secure the material.

A rubber gasket seals the garage door where it contacts the cement floor. Most are installed in twin tracks near the bottom of the door and replacements are available in standard lengths. On most doors, a screwdriver can be used to pry open the end of the tracks and allow you to pull out the existing, worn-out gasket. After lubricating the tracks with spray silicone, the new gasket can be threaded into the track. Methods for securing the protruding ends of the gasket around the end of the door differ, so consult the directions that came with the gasket.

For answers to your questions about adequate garage insulation or to find a contractor specialist in the southeast, contact AirConditioningSouthEast.com