In this article:

• How much insulation is enough?
• Where insulation belongs
• Types of insulation
• Having insulation installed

Are you spending too much on your energy bills? If your home’s insulation isn’t up to snuff, you may well be. According to the U.S. Department of Energy, 44% of the energy used in the average American home goes toward heating and cooling. If your attic, walls, or floors are underinsulated, a large part of your costly conditioned air may be making a beeline for the great outdoors.

Insulation saves you money by minimizing heat loss and reducing drafts, making a house more comfortable. Some types seal out air infiltration, a major contributor to heat loss. Just how well insulation resists heat flow is measured and rated by an R-value. Insulation materials differ in their R-values per inch of thickness.

How much insulation is enough?
Houses built in the last few years may or may not have optimal levels of insulation, depending on how much attention was given to energy conservation when they were built. But nearly all older homes are likely to be lacking. The best way to find out if your house has enough is to call your local utility company and request information about getting an “energy audit.”

Recommended minimum R-values for homes vary by climate and may be affected by how a house is built and the type of heating used. Here are a few rules of thumb:

For mild climates, have R-11 in the walls and floors and R-19 in ceilings below ventilated attics. For moderate climates, have R-19 in the walls and floors and R-30 in ceilings below ventilated attics. For cold climates, have R-19 in walls and under floors and R-38–R-49 in ceilings below ventilated attics. (Visit the Department of Energy’s website at www.energy. gov for more specific recommendations by region.)

Where insulation belongs

Insulation should be installed inside any barrier that’s located between heated and unheated spaces. In essence, it should form an envelope around a home.

The attic is the most important place for insulation. Buttoning up an uninsulated attic can cut fuel bills by 30%. Bringing a minimally insulated attic up to optimum insulation levels can yield comparable results relative to the amount added. And, if an attic is unfinished, insulating it is a relatively easy job.

If an attic is finished with walls and ceilings, insulation should be installed in the end and knee walls, the ceiling joists beyond the knee walls, and, if possible, between rafters of the attic ceiling (however, ventilation between the rafters from the eaves to the ridge should not be blocked).

It’s also important for house walls to be insulated, but, in an older, uninsulated house, this doesn’t always pencil out. Insulating walls during construction before wall coverings are applied is a breeze, but insulating them after the fact is an expensive and complicated proposition (unless you’re remodeling or re-siding the house). If your home has uninsulated walls and is located in a cold climate, ask two or three insulation contractors for bids, and then figure out how long it will take to pay back the cost at a savings of 16%–20% per year on your energy bill.

Insulating crawlspaces is also helpful; doing so can trim 5%–15% off heating costs. If crawlspaces are reasonably accessible, insulating is generally pretty easy. Outer walls and foundations in finished basements also should be insulated.

Types of insulation
It’s easiest to consider the various insulation materials by category (though there is some overlap): batts and blankets, loose-fill, blown-in, plastic foam, rigid boards, and reflective. These categories are based primarily on the material’s form and installation method.

The batts-and-blankets variety is most familiar to homeowners and the type most commonly installed by do-it-yourselfers. The main insulating material is mineral fiber, either fiberglass or rock wool fibers. Batts are sold as precut strips and blankets as continuous rolls. Both are sold in widths that match conventional wall-stud and ceiling-rafter spacings so they may simply be pressed or stapled into place. They are sold both with and without kraft or reflective foil/vapor- retarder facings. (A vapor barrier is faced toward the warm-in-winter side; types without a barrier are used when adding to existing insulation.)

The advantages of batts and blankets are that they’re readily available, easy for do-it- yourselfers to install, and relatively affordable. Installing them in non-standard stud or joist spacings takes a little extra time since the material must first be cut with a utility knife.

Loose-fill insulations—meant to be poured, stuffed, or blown in place—are made from glass and rock wool fibers, cellulose fiber, or expanded vermiculite and perlite. They’re made from the same spun minerals as batts and blankets but are left loose or made into pellets. They’re used in attics and walls.

Cellulosic insulation is made from recycled paper and wood fiber treated with a fire retardant. It’s used in both attics and walls.

Vermiculite is made from mica ore, and perlite comes from volcanic rock; both are heated and expanded into a fluffy, non-combustible material that is used to insulate ceilings and some walls (mostly concrete block).

Loose-fill materials are sold in bags or bales and work well for insulating between ceiling joists in an accessible attic. To fill up wall cavities, pneumatic equipment is often necessary. When using loose-fill insulation in an attic, it’s usually necessary to install a vapor barrier (such as plastic sheeting) first.

Having insulation installed

Before hiring a professional to insulate your home, get two or three bids. To compare apples with apples, be sure each bid clearly describes the material to be used and specifies the R-values that will be installed in each area of the house. When the material arrives, bags should be labeled with R-value information; with loose-fill insulation, check to be sure the appropriate number of bags is installed.

Also talk with your contractor about both ventilation and moisture control. Ventilation is important to ensure your home’s air quality is maintained without unnecessary energy loss. And in most climates vapor barriers must be installed when you insulate to prevent vapor, naturally present in the air, from collecting inside insulated walls, ceilings, floors, and roofs. In most climates, a vapor retarder—such as the foil facing on batts and blankets or, with loose-fill, 6-mil polyethylene plastic sheeting—must be installed at the warm-in-winter side of the insulation. Existing walls that are filled with blown-in insulation can be coated with a low-permeability paint to repel vapor.

Last but not least, be sure to seal up all cracks and crevices that allow air infiltration, using caulking compound and weatherstripping. Doing so is key to capitalizing on the energy savings and comfort of your new insulation.