How To Insulate Your Garage

Create the ideal climate in your man cave by adding insulation.

If a man’s home is his castle, then the garage is the ultimate playpen. After all, it’s where we keep our best and most expensive toys – everything from automobiles and motorcycles to woodworking machines and other pricey equipment. But often the garage is more like a dungeon: too hot, too cold or too drafty to comfortably work in (let alone hang out in with our buddies). The good news is that, just like other living spaces, the garage can be insulated to create a comfortable environment in which to work, play, entertain or create.

Insulating your garage is an easily accomplished task for most homeowners. Some types of insulation, such as Dow's SafeTouch shown here, don't require the usual safety gear.

Though many types of insulation materials – from cotton and wool to recycled paper and even shredded blue jeans – have been tried throughout the years, a handful have proved to work best in modern stud-frame construction. They all provide decent insulating properties, and with the proper tools and the right safety gear, you can install most of them yourself with minimal effort.

At times referred to as “glass wool,” fiberglass insulation has been around for decades and basically consists of molten glass that’s been spun into very thin threads. Although it is available as a loose-fill material (which requires you to rent a mechanical blower to install), the most common type of fiberglass insulation comes in blanket form, also known as “batts” (photo below). Available in various densities, widths and lengths to fit specific stud-bay configurations, batts are sold with or without an attached vapor barrier, which is typically installed toward the “warm-in-winter” portion of the home to help combat moisture vapor’s natural tendency to move to a cold surface where it can condense.

Fiberglass insulation is not only the most common type available but also the most economical. Because its abrasive fibers can penetrate skin and irritate the lungs, it’s important to wear proper safety gear when installing it.

Residential fiberglass batts often contain a resin binder that can emit formaldehyde fumes into the air. Some brands off-gas faster than others, but over time any insulation that uses formaldehyde can cause lung irritation in people who are sensitive to formaldehyde exposure.

Although fiberglass is the least expensive of all insulation choices, its low density makes it susceptible to every mode of heat transfer, and its insulating value is less dependent on the material itself than it is on the air trapped in the fibrous web. Therefore the smallest error in installation can dramatically affect its performance.

When installing fiberglass, it’s imperative that you wear the correct safety gear: goggles, a dust mask or another form of respirator, long pants and a long-sleeve shirt. For added protection, tape your pant legs around your ankles and your sleeves around your wrists. After you’ve installed the insulation, wash your work garments separately to avoid contaminating other clothing.

Cellulose insulation is made mostly from shredded newspaper mixed with a variety of chemicals to reduce its flammability. Typically installed by a professional, it is blown into wall cavities in either new construction or an existing structure that already has finished interior walls.

Blown-in cellulose has a similar R-value to that of traditional fiberglass, but it is usually thinner – often by as much as 2 to 3 in. It does a good job of suppressing heat transfer by convection, but it is susceptible to heat transfer by conduction and relies heavily on the low conductivity of its fibers for its insulating properties. Although it can be installed in many existing structures, it may cause some corrosion on metal that it touches.

Rigid foam
Applied either to the interior of a wall between the studs or on the exterior of a structure between the sheathing and the siding, rigid foam insulation can be an effective choice for insulating a garage. It consists of large stiff boards of varying thicknesses of different foam materials. The most common types include expanded polystyrene (EPS), extruded polystyrene (XPS) and polyisocyanurate (ISO).

Rigid foam is available in a variety of thicknesses and R values. Specific installation care is required, as foam can break down from prolonged exposure to sunlight and is susceptible to damage by certain types of adhesives.

EPS is a white closed-cell material that has the lowest average R-value of all rigid foam products (about R-4 per inch). At about 19 cents a square foot, it’s also the least expensive. Besides being formed into sheets of insulation, EPS is used to make everyday items such as coffee cups and shipping materials.

Easily recognized by its blue, green or pink color, XPS falls in the middle of the foam category both in R-value and price. At about R-5 per inch, XPS costs about 42 cents a square foot and is available both with and without a facing.

ISO panels are expensive, costing as much as 70 cents a square foot for a 1-in.-thick panel, but at about R-6.5, they have the highest insulating properties of all the rigid foam products. ISO panels are always faced, often with a foil covering, and are typically used as a covering over exterior wall sheathing.

All types of rigid foam insulation have specific installation requirements, so it’s essential to follow the manufacturer’s instructions, both in interior and exterior applications.

Spray foam
Polyurethane spray-foam insulation is a two-part system that’s available in a two-tank kit for small DIY applications, or it can be professionally applied by an insulation contractor. Spray foam relies on the low conductivity of the gas or trapped air within its cellular structure and the low conductivity of its plastic content to create a high R-value.

Because of its fluid nature, spray foam is ideal for getting into small spaces and filling all air gaps. DIY kits are available for smaller areas; professional installers can apply it to larger areas, as shown here with Dow’s Styrofoam brand spray polyurethane.

Spray foam expands to about 100 times its original volume and creates an airtight cavity that effectively fills in all air gaps. It can be applied between wall studs and sprayed to the underside of garage roof sheathing to enhance the roof’s thermal performance.

For filling gaps, cracks and air leaks, spray foam is also available in small cans (see photo below). Products such as Great Stuff can be used in a variety of applications and can go a long way toward making your garage a comfortable place.

For sealing small air leaks or other gaps that would allow heat to enter or escape, use individual cans of spray foam, such as Great Stuff.

Alternative materials Although fiberglass may be the most-often purchased insulation material, air-quality concerns and the care that’s required to properly and safely install it have prompted the development of alternatives. For example, Dow’s SafeTouch is made from the same fibers used to make clothing and bedding, so it’s soft, it doesn’t irritate skin, and you don’t need to wear special protective gear when installing it. As an added benefit, it’s made without formaldehyde, acrylic binders or borates, so it doesn’t emit any fumes that might cause breathing or allergy problems.

Another alternative insulation material (which has been available for many years but has been overshadowed by fiberglass) is slag, rock or stone wool (photo, below). Manufactured from molten rock through which a stream of air or steam is blown, the material is spun at high speeds in a process similar to making cotton candy, and the result is a mass of fine intertwined fibers with a typical diameter of 6 to 10 micrometers.

Rock-wool insulation, such as that from Roxul, is made from basalt rock and recycled slag. According to the manufacturer, it is resistant to rot, mildew, mold and bacteria growth.

Choosing what’s best for you
Considering all of the choices available, picking the right insulation for your garage may seem daunting. So it’s reassuring to know that any of these products will make your space more comfortable. When properly installed, these materials will deliver years of performance and will help you control heating and cooling expenses.

Although the cost of materials should always be considered, don’t let it become the only deciding factor when choosing what to use in your garage-insulation project. Consider which material will deliver the best performance and the greatest return on investment. If you plan to do the work yourself, factor in ease of installation. The best insulation solution may combine multiple materials, such as fiberglass batts within the walls and spray foam for the ceiling.

Insulating your garage will not only increase your home’s overall value but also contribute to a better quality of life. Reduced road noise, fewer pests and more comfortable temperatures are just a few of the benefits. When you consider the rewards, the question becomes not what insulation to use, but why you didn’t insulate your garage sooner.

To make the best decisions about your garage’s insulation, it’s essential to understand two concepts: heat transfer and R-value.

Heat transfer explains how heat moves from the warm side of the insulation to the cold side in three ways: radiation, conduction and convection. Radiationsuch as the warmth that is created by sunlight, is the transfer of heat from one object to another through airspace. Conduction, on the other hand, is the transfer of heat between two objects that are actually touching. For example, if it weren’t for the air that’s trapped within their structure, insulation materials such as mineral wool or fiberglass would actually transfer heat from the outside wall to the inside wall simply because the material touches both surfaces. But while trapped stationary air within insulation helps its performance, moving air – convection – hinders it. Convection can occur when cold air displaces hot air, causing it to rise and create what’s known as a “convective loop,” which can transfer heat out of the home in winter and into it during the summer.

To combat heat transfer, it’s necessary to increase a wall surface’s R-value – the higher the R-value, the greater the insulating power. Manufacturers of insulation products print the R-values of their products either on the packaging materials or on labels. In most cases, R-values are also printed on the facings of fiberglass batts and rolls.

Although some manufacturers promote the “per inch” R-value of their products, the overall R-value when the product is installed is what counts. Common R-values for home- and garage-insulation products range from R-8 to R-38, depending on the materials.

Bonus Video: