Understanding Insulation - Spending Too Much?

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% 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 retards heat in its natural quest to move from a warmer to a cooler space. In the winter, when warm room air exits through walls, rises up through the attic and roof, and flows down through the floor, insulation blocks--or at least slows--its departure. And in the summer, when warm outdoor temperatures try to force their way into your air-conditioned rooms, insulation holds the heat at bay.

By slowing heat movement, insulation not only saves energy but reduces drafts, making a house more comfortable. Some types--foam in particular--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 (see chart at right). Insulation materials differ in the R-values they will deliver 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, R-11 in the walls and floors and R-19 in ceilings below ventilated attics. For moderate climates, R-19 in the walls and floors and R-30 in ceilings below ventilated attics. For cold climates, R-19 in walls and under floors and R-38 to R-49 in ceilings below ventilated attics. For more specific recommendations by region, call or write the Department of Energy for their Information Fact Sheet (see Resources).

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's living spaces.

The attic is the most important place. Buttoning-up an uninsulated attic can cut fuel bills by 30%. Bringing a minimally-insulated attic up to optimum 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 then figure out how long it will take to pay back the cost at a savings of from 16% to 20% of your fuel bills.

Insulating crawl spaces is also helpful--doing so can trim from 5% to 15% off heating costs. If crawl spaces 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 in these groups): batts and blankets, loose-fill, blown-in, plastic foam, rigid boards and reflective insulation. These categories are based primarily on the material's form and the method of its installation.

Batts and Blankets

These are the 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 pre-cut 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--the material must first be cut with a utility knife.

Loose-Fill Insulations

These are 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--only they're left loose or made into pellets. They're used in attics and walls. 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 (see below).

When using loose-fill insulation in an attic, it's usually necessary to install a vapor barrier (such as plastic sheeting) first. 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 cavities between wall studs.

The insulation itself may consist of cellulose, loose mineral fibers, fiber pellets or fibers that are coated with an adhesive (the latter type being the most effective at sealing a cavity and 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. NOTE: Urea-formaldehyde foam-in-place insulation should not be used because of potentially dangerous vapor emission.

Cellulosic insulation

This material 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).

Rigid foam board insulation

These 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 re-roofing) 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 indoors. The panels may have foil facings on one or both sides to reflect heat.

Reflective insulations

Made from aluminum foil, these 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 are 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, for 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.

And 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.


An R-value indicates an insulation's resistance to heat flow. The higher the R-value, the greater the insulating effectiveness.

The R-value depends on the type of insulation and includes its material, thickness, and density. When calculating the R-value of a multilayered installation, add the R-values of the individual layers. Installing more insulation in your home increases the R-value and the resistance to heat flow.

The effectiveness of an insulation's resistance to heat flow also depends on how and where the insulation is installed. For example, insulation that is compressed will not provide its full rated R-value. The overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists. Therefore, it's important to properly install your insulation to achieve the maximum R-value.

The amount of insulation or R-value you'll need depends on your climate, type of heating and cooling system, and the section of the house you plan to insulate

What is the basic difference among fiberglass, rock and slag wool, cellulose, and foam insulations?

Fiberglass is made from molten sand or recycled glass and other inorganic materials under highly controlled conditions. Fiberglass is produced in batt, blanket, and loose-fill forms.

Rock and slag wool are manufactured similarly to fiberglass, but use natural rock and blast furnace slag as its raw material. Typical forms are loose-fill, blanket, or board types.

Cellulose is a loose-fill made from paper to which flame retardants are added.

Foam insulations are available as rigid boards or foamed-in-place materials that can fill and seal blocks or building cavity spaces. Foams are also used in air sealing to fill gaps, cracks, or openings.

Reflective materials are fabricated from aluminum foils with a variety of backings such as polyethylene bubbles and plastic film. Reflective insulations retard the transfer of heat; they can be tested by the same methods as mass insulation and therefore assigned an R-value.

A Radiant Barrier is a building construction material consisting of a low emittance (normally 0.1 or less) surface (usually aluminum foil) bounded by an open air space. Radiant barriers are used for the sole purpose of limiting heat transfer by radiation.

How much will I save by adding insulation to the walls, ceilings, and floors of my home?

Insulation saves money, increases home comfort, and protects the environment by reducing energy use. According to the U.S. Department of Energy (DOE), the typical U.S. family spends close to $1,500 each year on energy bills. DOE statistics show that, typically, 44% of a homeowner's utility bill goes for heating and cooling costs. DOE states that homeowners may be able to reduce their energy bills from 10% to 50% by taking certain steps. One of the major steps is increasing the amount of thermal insulation in their existing homes or purchasing additional insulation when buying new homes.

Unless your home was constructed with special attention to energy efficiency, adding insulation will probably reduce your utility bills. The amount of energy you conserve will depend on several factors: your local climate; the size, shape, and construction of your house; the living habits of your family; the type and efficiency of the heating and cooling systems; and the fuel you use. Energy conserved is money saved, and the annual savings increase when utility rates go up. Insulation upgrades also add to the value of your home.

The U.S. Department of Energy recommends home insulation R-values based on where you live. These recommendations are detailed for various sections of the home including walls, ceilings, and basements. Click here to view these R-value recommendations on a U.S. map or view these recommendations from the R-value calculator. You can then use the U.S. Department of Energy's Zip-Code Insulation Program to determine how much insulation you should add and where to achieve the recommended insulation levels for maximum energy efficiency.