The Best Types of Attic Insulation
Choose from these types of attic insulation to keep your house warm and your attic dry and mold-free. You'll also extend the life of your roof.
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Insulating an Attic
Have you been feeling a little cold in your house lately? Noticing your energy bills creeping upward? Seeing areas of your roof where snow melts more slowly than others? Perhaps you’ve detected moldy odors in your attic or seen mold growing on the framing.
All these signs indicate you need more attic insulation.
Attics need to be thermally separated from the rest of the house to keep warm air out. Warm air raises humidity levels, which promotes mold growth. It also heats up the roof and creates ice dams that break down the roof covering and cause leaks. And, of course, losing heat through a poorly insulated ceiling will drive up your heating costs
There are many types of attic insulation. One factor to consider when choosing between them is how much thermal protection your attic needs.
R-value, a measure of thermal resistance, varies by location. R-30 is the minimum requirement in Southern states and R-49 for Northern states. Ease of installation is another thing to think about, especially if you plan to do the work yourself.
There are also environmental considerations, although most insulation materials are made from abundant or recycled materials.
Here’s a rundown of the four types of attic insulation materials and installation methods at your disposal.
Air is one of the best thermal insulators, and fiberglass insulation makes use of it. Manufactured from glass fibers, fiberglass is woven into loose cotton candy-like bundles that can be installed multiple ways:
- Batts are bundles of a pre-determined thickness sized to fit snugly between the attic joists. You can buy batts with Kraft paper facing for walls, but in the attic they should be unfaced to allow the fiberglass to breathe. They’re installed by laying them in place and stuffing extra insulation in gaps around pipes, electrical boxes and other obstructions.
- Rolls are the same width as batts and about 40 feet long. They’re easier to install in long attic bays.
- Loose-fill fiberglass is typically installed with a blower. This method is easier and less time-consuming than laying batts, and allows you to adjust the thickness to achieve the optimum R-value. Blowing in loose fill supplements an attic with some insulation, but not enough. Just buy the insulation, rent a blower and have at it. Be sure to wear protective clothing, a respirator and goggles to protect yourself from the glass fibers. They aren’t carcinogenic like asbestos, but are still irritating and can cause respiratory distress.
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A green product derived primarily from recycled newspaper, cellulose insulation comes in a loose-fill format. Because it’s an organic material, cellulose is flammable. That means must be treated with a flame retardant to be safe as insulation. Most products are also treated with boric acid to repel mold and pests.
Cellulose is safer to install than fiberglass because it doesn’t irritate the skin and eyes. After application, it settles to form a denser insulating layer that provides some sound insulation. It costs about the same as fiberglass. Keep in mind cellulose absorbs moisture, so if you have a damp attic you may need to install a vapor barrier over it.
Mineral Wool Insulation
Also known by the brand name Rockwool, mineral wool insulation is manufactured by melting basalt rock together with slag — a byproduct of the copper and steel industry — and spinning the resulting material into fibers. The fibers are then woven into batts about the same size as fiberglass batts.
Mineral wool batts are thicker and denser than fiberglass ones. They’re also waterproof, crucially for attics with moisture problems. The batts won’t clump. And because they repel water, mold can’t grow on them. Their extra bulk also provides better soundproofing. Mineral wool batts are about 25 percent more expensive than fiberglass.
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Spray Foam Insulation
Many builders consider spray foam to be the gold standard for attic insulation. Inch-for-inch, it offers a higher R-value than other materials. It’s also moisture- and mold-resistant, and permanently seals cracks, gaps and other air passageways.
As you might expect, spray foam is also significantly more expensive than other insulation materials, and due in part because you almost always need professional installation.
Spray foam comes as a liquid, sprayed with a machine that resembles an airless paint sprayer. It expands and hardens on contact with air. Although the cured foam is chemically inert and non-toxic, toxic fumes are released during spraying. That, together with its incredible stickiness, is why it needs to be professionally installed.
Note: You can only install foam in an attic without any other type of insulation.