Are you spending too much on your monthly energy bills? If your home’s insulation isn’t up to snuff, you may well be. According to the Department of Energy, 44 percent of the energy used in the average American home goes toward heating and cooling. If your attic, walls, or floors are under- insulated, 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 upon how much attention was given to energy conservation when they were built. But nearly all older homes, unless recently retrofitted with insulation, are likely to be lacking. The best way to find out whether or not your house has enough is to call your local utility company for information on 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, use R-11 in the walls and floors and R-19 in ceilings below ventilated attics. For moderate climates, use R-19 in the walls and floors and R-30 in ceilings below ventilated attics. For cold climates, use R-19 in walls and under floors and R-38 to R-49 in ceilings below ventilated attics. For more specific recommendations by region, visit the Department of Energy’s website at www.energy.gov.
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 percent. 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 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 eaves to 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 difficult 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 to 20 percent of your fuel bills.
Insulating crawlspaces is also helpful; doing so can trim 5 to 15 percent 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 major categories (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 the method of installation.
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 be simply 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 at nearly all building supply centers, 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 several materials: glass and rock wool fibers, cellulosic fiber, and expanded vermiculite and perlite. Loose-fill fibers are made of the same spun minerals as batts and blankets, but they’re left loose or made into pellets. They’re used in attics and walls.
Cellulosic insulation is made from recycled paper (mostly newspaper) and wood fiber that has been 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.
R-values per appx. 1" thickness Material | R-value
per 1" |
| Fiberglass batt & blanket | 3.27 |
| Rock wool batt & blanket | 3.2 to 3.7 |
| Fiberglass loose fill (blown) | 2.2 to 4.0 |
| Rock wool loose fill (blown) | 2.9 to 3.6 |
| Cellulose loose fill (blown) | 3.2 to 3.8 |
| Vermiculite loose fill (poured) | 2.27 |
| Perlite loose fill (poured) | 2.7 |
| Sprayed polyurethane foam | 6.0 to 7.3 |
| Fiberboard sheathing | 1.32 |
| Expanded polystyrene (extruded) | 5.0 |
Expanded polystyrene (molded)
| 3.85 to 4.35 |
| Polyisocyanurate board (unfaced) | 5.8 to 6.2 |
| Polyisocyanurate board (faced) | 7.1 to 8.7 |
Blown-in loose-fill insulation is installed by professional installers or, in some cases, homeowners who rent the special pneumatic equipment needed. Effectiveness is a direct result of the application technique, so it’s usually best to have this done by a pro.
The material is loaded into a machine that then fluffs and blows it through a hose into the areas between ceiling joists or the cavities between wall studs. The insulation itself may consist of cellulose, loose mineral fibers, fiber pellets, or fibers coated with an adhesive (the latter type being the most effective at sealing a cavity and the least prone to settle once inside a wall).
Foamed or sprayed-in-place insulation (typically polyurethane) is installed by professionals who have special equipment for monitoring the mix and application. It provides very high R-values, doesn’t shrink or settle once in place, blocks drafts caused by air infiltration because it conforms to every nook and cranny, and offers a barrier to moisture.
Sprayed-in-place types are designed for new construction and can be used in walls, beamed ceilings, and around the foundation’s perimeter. They are relatively expensive. Take special note: Avoid urea-formaldehyde foam-in-place insulation because of potentially dangerous vapor emissions.
Rigid foam-board insulations are made from a number of different materials: asphalt-impregnated fiber board, polystyrene, polyurethane, and polyisocyanurate. These rigid panels are generally used in new construction (or re-siding and reroofing), where they may be installed as wall or roof sheathing, insulation beneath interior walls, or around foundations. Because they are classified as combustible, they cannot be left exposed. The panels may have foil facings on one or both sides to reflect heat.
Reflective insulations, made from aluminum foil, are most effective in hot climates at blocking radiant heat. Effectiveness depends on whether the foil is simply a flat sheet, used to block heat transfer through roofs, or a barrier that has multiple layers separated by air spaces, appropriate for reducing heat gain through roofs, ceilings, walls, and floors.
Getting it done
Before hiring a pro to insulate your home, get two or three bids. To compare apples with apples, be sure each bid clearly describes the material being 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 be sure 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.
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