This article was originally published in the September/October 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online September/October 1996

insulator using wet-spray cellulose


In the photo above, a new wall is insulated with wet-spray cellulose. After spraying, the insulation is trimmed down to an even level and then allowed to dry before closing the wall. Wastes are swept up and reused. 

by Jeanne Byrne

Home Energy's Consumer

If you're considering insulating, here's a guide to help you decide where to insulate, how much to install, and what type of insulation to choose.

Between 50% and 70% of the energy consumed in the typical American home goes toward heating and cooling, accounting for a large chunk of the total energy bill. Often, too little insulation and too much air leakage mean that a lot of this energy is being wasted.

Insulation not only saves money, it makes your house more comfortable. Walls, ceilings, and floors stay warmer in the winter and cooler in the summer, which helps maintain a uniform temperature throughout the house. Insulation can also cut down on noise from outside.

You'll get the most out of your insulation if you choose and install it correctly. You may be able to do the job yourself, or you may prefer to hire a professional insulation contractor. Either way, there are some new insulation materials available, along with new techniques that make insulation easier to install so that it performs well.

<img nosave= data-cke-saved-src=../picts/96092201.gif src=../picts/96092201.gif alt=insulator using x-sas-useimagewidth= x-sas-useimageheight= blow-in= blanket= system= = border=2 height=219 width=144>Controlling Air Leakage). You may never get another chance once the holes are hidden under a foot or more of insulation.

Types of Insulation

Some of the common materials used for insulation are glass fibers (fiberglass), fibers of molten rock or slag (rock wool), recycled newspapers (cellulose), urethane foams, and even recycled cotton fibers. Insulation comes in several forms--loose fill, batt, blanket, rigid board, or expanding spray foam.

Loose-Fill Insulation

Loose-fill insulation consists of loose fibers or granules, and is made from cellulose, fiberglass, rock wool, cotton, or other materials. This loose insulation conforms to the space in which it is installed. Loose-fill insulation comes in bags, and is usually blown into cavities or attics with special equipment. Insulation is sometimes blown at relatively high density into a wall or ceiling cavity to resist air infiltration--this technique is called dense-pack.

Sometimes loose-fill fibers are cosprayed with an adhesive or water in order to cover irregularly shaped and hard-to-reach areas or to install in walls before drywalling. The insulation dries within a few days and is resistant to settling. This technique is often used with cellulose and is called wet spray. Waiting for the insulation to dry before adding a vapor barrier to the wall can be inconvenient, so some newer processes (moist spray) use a lot less water to speed up drying time. Some installers also use drying machines.

Insulation can also be blown into open wall cavities by attaching a barrier to the studs to hold it in. In one system, a reinforced transparent vapor barrier is stapled to the studs and cellulose is blown in through small holes, which are later patched. A similar process involves blowing fiberglass into stud cavities behind a net. Another system uses a temporary frame to pack cellulose, fiberglass, or rock wool densely into the cavities. The densely packed insulation stays in place when the frame is removed.

Batts and Blankets

Batts and blankets are flexible, bound insulation made from glass or cotton fibers. They come in rolls or strips in standard widths, usually to fit between framing on 16- or 24-inch centers; thickness varies depending on the R-value desired. Blankets are available in continuous rolls, whereas batts are precut.

Batts and blankets can fit under floors, in attics, and in unfinished walls. Batts are easier to handle than blankets, but blankets can be cut with a knife or razor for a perfect fit, minimizing waste. Both are available with or without vapor retarder facings. 

insulator installing  dry cellulose insulation


An insulator at Canada's EnviroHome installs dry cellulose insulation. The cloth mesh stapled across the studs helps contain the cellulose during the installation process. Because of the dust generated, this man should be wearing eye protection in addition to his dust mask. 

Rigid Insulation

Rigid insulation is made from fibrous materials or plastic foams and is pressed or extruded into boardlike forms. These provide thermal and acoustic insulation, added structural strength, and air sealing.

Plastic foam board (or rigid foam) is the most expensive form of insulation and is made from polyurethane, polyisocyanurate, or polystyrene. It is commonly used in exterior walls (under the siding) and foundations. Since it provides a high R-value per inch of thickness, it is useful where a lot of insulation is desired in cramped quarters, such as cathedral or vaulted ceilings. Foam insulation must be covered with finishing material for fire safety.

Rigid insulation is being used in innovative ways in new construction. Stressed skin walls can replace traditional framing with panels consisting of a foam core with structural sheathing glued to both sides. They usually use expanded polystyrene (EPS) or polyurethane foam, and are impermeable to moisture on both sides. Some new stressed skin wall systems actually use compressed wheat straw sandwiched between oriented strandboard (OSB). These also have high R-values, and have been used in other countries for years.

fiberglass batt


The fiberglass batt is one of the most well-known insulation types. Here, installers have carefully cut batts to fit around pipes and electrical outlets, insuring complete insulation coverage. 
Another new construction technique uses all-in-one exterior insulation and finish systems (EIFS) that have a finish similar to stucco and can be cut in various shapes. Unfortunately, many homeowners have had wall decay and termite problems when moisture became trapped under the EIFS. Meticulous installation is critical to avoid such problems.

Some builders now use rigid foam form blocks--generally made from expanded polystyrene--stacked so that their hollow centers are aligned. The cavities are then filled with concrete, and sometimes reinforcing bars, to create an insulated structural concrete wall.

Foam in Place

Foam-in-place materials require special equipment to meter, mix, and spray or extrude into place. They provide air sealing as well as insulation. Polyurethane and polyisocyanurate foams have high insulation values per inch. Another type of foam, called Icynene, is also becoming more popular in energy-efficient new construction. These foams can be sprayed into open wall cavities, where they expand to fill the space. Excess material is then trimmed off and, in some cases, used in the attic as loose fill. Spray foams are particularly helpful for insulating difficult areas like sill plates. 

Radiant Barriers

Radiant barriers are made of aluminum foil with backing. Rather than slowing heat conduction as insulation does, they stop heat from radiating through the attic. Radiant barriers can reduce attic temperatures in hot climates, so that the difference in temperature between the house and attic is not so great. Based on the same concept, a radiation control (reflective) coating on the roof can lower the summer roof temperature in hot places. Since they reduce radiant rather than conducted heat, it is difficult (and inappropriate) to associate R-values with radiant barriers or radiation control roof coatings.

Figuring Out What You Need

How much insulation your house should have depends on your climate, energy costs, budget, and personal preference. You may be able to get guidance on insulation levels appropriate for your area from your utility's energy conservation department, the local or state building code, an independent energy auditor, or an insulation contractor. Remember that the building code gives the minimum legal level of insulation for new homes. Put in more if you have high energy bills or want to be more comfortable.

The U.S. Department of Energy (DOE) has a list of recommended levels of insulation in ceilings, walls, floors, and foundations, broken down by zip code. In general, you should put at least R-30 in your attic even in milder climates, and up to R-49 in the coldest parts of the United States. Floor insulation may not be necessary at all in the warmer states, but in most parts of the country R-19 is recommended. Wall insulation is recommended in all climates, but the amount can be limited by the space in the wall cavity. Using fiberglass or cellulose in a 2 x 4 wall will usually give you from R-11 to R-13. However, you can get R-19 in a 2 x 6 wall cavity, and even more if you use rigid insulation beneath the siding. Call the Energy Efficiency and Renewable Energy Clearinghouse for DOE's specific recommendations for your zip code.

It is almost always easier and more effective to install more insulation during initial construction than to add it later. If you're building a new home, make sure all the areas in Figure 1 are insulated to code or beyond. Some areas are impossible to go back and insulate after the house has been built--for example, the sill plate (the joint between the top of the foundation and the bottom of the house frame).

Still, you can add insulation to most places in existing homes. Attics are typically the easiest to get to, but insulation can be blown into empty wall cavities, attached under floors, and added to basement or crawlspace walls. On the other hand, retrofit foundation insulation may be prohibitively expensive, and adding more insulation to partially insulated walls is usually difficult and impractical. 

rigid foam insulation


Rigid foam insulation can be used in exterior walls (under the siding), foundation, and other places where space is limited. The high R-value per inch of thickness is especially useful where a lot of insulation needs to fit into a small amount of space. 

How Much Do You Have Already?

To decide how much insulation to add to your home, you need to know how much is already there. If you don't have an energy auditor inspect your home, you should look for insulation in several places.

Check all the recommended insulation areas in Figure 1. In each location, measure the thickness of the insulation and identify which type of insulation was used (see Table 2). First, check the attic; take a few measurements with a ruler in different areas (away from the access hatch, where insulation is more likely to have been disturbed or compacted) and average them.

In unheated garages and basements and above crawlspaces, the structural framing (the joists of the floor above, or the wall framing studs) is often exposed, making it easy to examine the insulation. You may find batts, blankets, or rigid insulation there. An unvented crawlspace may also have insulation on the perimeter wall.

]If your house is relatively new, it may have insulation outside the basement or foundation wall. However, this insulation will not be visible, because it will be covered by a protective layer of plastic, fiberglass, metal flashing, or rigid protection board. The builder or the original homeowner may be able to tell you if such exterior insulation was used.

Next, inspect exterior walls. One method is to remove the cover plate from an electrical outlet or switch on the inside of the wall, and shine a flashlight around the sides of the box. Often you can catch a glimpse of insulation in the gaps around the outlet box. A plastic crochet hook (don't use metal unless you first turn off the power to the outlet) is useful for pulling out a bit of the material for identification. Check outlets on a few different walls on each floor, and make a separate check in any parts of the house that were built at a different time. Rigid insulation is difficult to identify in finished walls. One way to look for it is to remove and then replace a small section of the exterior siding and sheathing.

Selecting a Type

The type of insulation you use will depend partly on the spaces that you plan to insulate. For example, since you cannot conveniently blow insulation into an open overhead space, batts, blankets, or spray products are used between the joists of an unfinished basement ceiling. The only way to fill closed cavities in finished walls (without tearing them open) is with blown-in insulation. Table 1 provides a summary of the appropriate applications for the various types of insulation. See Comparing Insulation Materials for other considerations in choosing which type to use.

Table 1: Insulation Comparison Chart


Installing Insulation

After planning the R-values and type of insulation that will be put into your home, make careful installation a priority. Batts are particularly susceptible to poor installation--it is easy to leave gaps that drastically reduce their effectiveness. Blown-in loose fill insulation can also be improperly installed. Some installers fluff the insulation (adding more air than they should), so that it takes up more space, but has a lower insulation value. Certain brands of loose-fill insulation come with an Inches = R-value guarantee; they are guaranteed by their manufacturer to achieve a given level of R-value when installed to a designated thickness.


Adding insulation to an unheated attic is usually straightforward. If there is no attic flooring, either loose-fill insulation can be blown in or fiberglass batts can be laid between the joists. If existing insulation comes up to the top of the joists, an additional layer of unfaced batts can be added perpendicular to the joists. This helps to cover gaps in the first layer. Insulation should be even and should cover corners. Also insulate and weatherstrip the access door or hatch. If access to the attic is limited, blown-in insulation will work best.

To ensure proper air circulation, make sure the insulation does not block vents. For roof vents, 12 inches of clearance is usually recommended. For eave vents, little clearance is necessary, as long as the vents are not obstructed. Keep insulation away from recessed light fixtures, and other fixtures that emit heat, to avoid fire hazards. Some newer recessed lights are IC (insulation cover) rated and can safely be buried by insulation.

Unless the attic already has some insulation, add a vapor retarder when you insulate. Most batts and blankets have a kraft paper vapor retarder on one side. This prevents excessive moisture from condensing in the insulation, which could reduce its effectiveness. The vapor retarder must be installed on the warm side of the insulation (face down in cold climates, face up in hot climates), or it can do more harm than good. When additional insulation is placed over existing insulation, do not install a vapor retarder, as it may trap moisture in the insulation underneath.

Do not store anything on top of ceiling insulation. When insulation is packed down, it tends to lose effectiveness.

Insulating a sloped cathedral ceiling can be much more difficult. There is little room between the ceiling and roof, and the cavity is difficult to access. The best method is to add rigid foam on the outside when reroofing. Another method is to drill holes in the drywall from the inside and blow insulation into the joist cavities. However, moisture can accumulate in the insulation if there is no ventilation in the cavity. Some people go so far as to build an attic and put on a new roof, so that there's more room for insulation.


Finished wall cavities are best insulated by an experienced contractor. The installer must drill holes in the sidewall and blow the insulation into each cavity between the studs.

For new construction, there are more options. Batts, wet-spray cellulose, or loose fill blown in through a barrier can be installed between the studs, and rigid board insulation can be put up before the siding is installed. Re-siding also presents a good opportunity to put rigid board insulation between the old siding and the new.

When installing batt insulation, don't compress it to fit behind electrical boxes--this will create areas around the boxes where the insulation is not fully expanded. Cut the insulation around any obstructions. Follow manufacturer's recommendations on stapling the facing to the studs.

Some people do use compressed batts for the whole wall, though. For instance, you can install a 6-inch R-19 fiberglass batt into a 3 1/2 inch stud cavity (which would normally take an R-13 batt). The compression will reduce the R-value to about R-17. This technique is especially useful in older homes, where 2 x 4 studs are truly 4 inches deep (modern 2 x 4s are only 3 1/2 inches deep).


If the basement space is unheated, it may be best to insulate between floor joists (basement ceiling) instead of around the foundation (basement floor and walls). Unfaced fiberglass batt insulation, supported from below with metal supports or wire mesh, can do the job. If you insulate above an unheated basement, also insulate any ducts or pipes running through this space (especially in cold climates where pipes might freeze), since the space will become colder in winter.
polyurethane foam insulation being sprayed


Polyurethane foam insulation is sprayed into open wall cavities. 
If you choose to convert an unheated basement into insulated living space, the simplest method is to build 2 x 4 frames against the concrete foundation walls, insulate with batts or blankets, and cover with drywall. Another method is to attach wood furring strips to the walls by nailing or bonding. The insulation can then be stapled or tacked into place. Drainage problems may need to be addressed to ensure that no exterior water leaks into the basement, and the concrete should be treated with water seal or vapor barrier paint.

Benefits of insulating the basement walls and floor can include decreased condensation (which can help prevent mold and mildew), reduced energy losses from ducts running through the basement, and reduced risk of pipes freezing in winter. 

Slab Floors

Insulating a slab foundation requires digging around the foundation at least 6 inches down. Attach rigid foam board; add a protective covering, such as fiberglass panels, treated plywood, or cement coating; then fill in and compact the soil. Although the slab will be insulated only at the edges, this is where most of the heat loss occurs.


If a crawlspace is ventilated, insulate the floor above it. Batts are generally installed between the floor joists and must be well supported so they don't sag or fall down. The batts should touch the floor boards continuously and should not be compressed. This is easier said than done. Insulating can be difficult while lying on your back, and getting the batts to stay up against the floor is a challenge. Common methods include using wire mesh (chicken wire) fastened to the joists under the batts, metal supports held up by tension between the joists, or wood lath supports attached perpendicular to the joists 18 inches apart. The best method is to use batts that are the exact thickness of the floor joists and support them with wire mesh. When you insulate the floor above a crawlspace, insulate all ducts and water lines running through the space, especially in cold climates where they might freeze.

Insulate crawlspace walls only if the crawlspace is dry all year, the floor above is not insulated, all ventilation to the crawlspace is blocked, and a vapor barrier (for example, 4- or 6-mil polyethylene film) is installed on the ground to reduce moisture migration into the crawlspace. Insulation batts can be fastened to the sill plate and draped down the wall. Because the insulation will be exposed, be sure to use either an unfaced product or one with the appropriate flame-spread rating. If you live in a very cold region, you should continue the insulation over the ground (on top of the moisture barrier) for about 2 feet from the wall.

fig. 1. Where to insulate in a home

Figure 1. Where to insulate in a home.

I In unfinished attic spaces, insulate between the floor joists.

2 In finished attic rooms with or without dormer, insulate:

2A between the studs of knee walls
2B between the studs and the rafters
2C between the studs of knee walls
2D extend insulation into joist space to reduce air flows

3 Insulate all exterior walls, including:

3A walls between living spaces and unheated garages or storage areas
3B foundation walls above ground area
3C foundation walls in heated basements

4 Insulate floors above cold spaces, such as vented crawl spaces and unheated garages, and:

4A any portion of the floor in a room that is catilevered beyond the exterior wall below
4B slab floors built directly on the ground
4C foundation walls of crawl spaces and perimeter plates
4D Extend insulation into joist space to reduce air flows

5 Caulk and seal around all windows and doors

If You Do It Yourself

Whether to install insulation yourself depends on several factors. Placing batts in the attic floor is usually relatively easy (if the attic is roomy), requiring only laying the material between the parallel ceiling joists. A homeowner can often insulate basement or crawlspace walls, or floors over unheated areas, using rigid, batt, or blanket insulation. Installing loose-fill insulation with blowing equipment is a job best left to the professional installer, and sprayed-on insulation also requires a qualified contractor. Adding insulation to a mobile home is complex and should generally be done by specialists, as well.

If you do decide to do it yourself, follow the manufacturer's instructions, and take these precautions:

  • Wear clothing adequate to protect against skin contact and irritation. A long-sleeved shirt with collar and cuffs buttoned, long pants, gloves, hat, safety glasses, and dust respirator are advisable in all do-it-yourself insulation projects.
  • Do not cover or pack insulation around bare stovepipes, electrical fixtures, motors, or any heat-producing equipment, such as recessed lighting fixtures unless they are IC rated--insulation can trap heat and prevent air from circulating. Install baffles to prevent insulation from getting within 3 inches of these fixtures.
  • Do not cover attic vents with insulation. Proper ventilation in attics helps prevent overheating in summer and moisture buildup all year long.



Table 2. Identifying Old Insulation
Material                        Description                     R-Value per inch(1)   Fiberglass batts            Pink, yellow, or white,                    3.2                              blanket-like    Loose-fill fiberglass       Pink, yellow, or white                     2.2                              loose fibrous material   Loose-fill rockwool         Denser than fiberglass,                    2.9                              wooly, usually grey                              with black specks                              (some newer products                              are usually white                                      Loose-fill cellulose        Shredded newspaper,                        3.5                              gray, dusty   Vermiculite                 Gray or brown granules                     2.2   Perlite                     White or yellow granules                   2.7   Misc. wood products         Sawdust, redwood bark,                      1                              balsa wood   Urea formaldehyde foam(2)   Whitish grey or yellow,                     4                              very brittle foam   Asbestos(3)                 May be mixed with other                     1                              materials--difficult                              to identify _____________________________________________________________________________   1. These R-values are for old insulation only. They take into account settling, as  well as average R-values for old materials that may have changed with new products.   2. Urea formaldehyde foam is no longer sold due to concerns about formaldehyde  off-gassing   3. If you suspect you have asbestos, consult a hazardous material specialist before  disturbing the insulation

If You Have It Done Professionally

Obtain cost estimates from several contractors for a stated R-value. But remember that you want good quality materials and labor, not just a good price. Ask them to describe the procedure they will use, as well as the insulation type and R-value.

Ask the contractor to attach vertical rulers to the joists prior to an attic loose-fill installation. This can help you to see if the proper depth was installed. Also, the installer should provide a signed and dated statement describing the type of insulation; the thickness, coverage area, and R-value; and the number of bags used or pounds installed.

You may want to have your attic R-value evaluated to ensure that you are getting what you paid for. Cookie-cutting (measuring and weighing a sample section of insulation) is the insulation industry recognized procedure of evaluating installed loose-fill insulation. Many independent companies offer cookie-cutting services to homeowners throughout the country. Contact the Insulation Contractors Association of America for a list of companies that offer these services.

Many companies offer home energy audits, in which professionals evaluate the energy efficiency of the home, identify the amount of insulation needed, and indicate where retrofits will be most economical. Energy utilities may also offer this service, as well as loans or other incentives to insulate. Another useful resource is the state energy office. Some states offer technical advice, tax credits for money spent on home insulation, and financing for retrofits. 

installer putting fiberglass rigid board insulation in place


This installer puts extruded polystyrene rigid board insulation in place. Like rigid foam, this board insulation fits in tight spaces. It can be installed in walls during new construction or when residing an existing wall. 


Loose-Fill Insulations, DOE/GO-10095-060, FS 140, Energy Efficiency and Renewable Energy Clearinghouse (EREC), May 1995.

Insulation Fact Sheet, U.S. Department of Energy, update to be published 1996. Also available from EREC. Call EREC with your insulation and other energy questions. Tel:(800)363-3732.

 Lowe, Allen. Insulation Update, The Southface Journal, 1995, No. 3. Southface Energy Institute, Atlanta, GA.

ICAA Directory of Professional Insulation Contractors, 1996, and A Plan to Stop Fluffing and Cheating of Loose-Fill Insulation in Attics, Insulation Contractors Association of America, 1321 Duke St., #303, Alexandria, VA 22314, (703)739-0356.

Jeanne Byrne is managing editor of Home Energy.



Controlling Air Leakage

Most people are aware that air leaks into their houses through small openings around doors and window frames and through fireplaces and chimneys. Air also enters the living space from other unheated parts of the house, such as attics, basements, or crawlspaces. It leaks in through gaps around electrical outlets and switch boxes, recessed fixtures, pull-down stairs, furred or false ceilings, and plumbing connections.

The attic--not the front door--is the best place to start air sealing. Hot air rises, and you're likely to find bigger holes between your house and attic than around doors and windows. Look for and seal the tops of wall cavities that open into the attic, especially over interior walls for the kitchen and the bathroom. Gaps may also be found where the attic level changes. In the basement, look at the joint where the basement ceiling meets the foundation wall. Seal all these holes before insulating, using gypsum board (such as Sheetrock) or any permanent rigid barrier, such as sheet metal, plywood, foam board, or cardboard. (Anything exposed should be fire resistant.) Cut the barrier to fit and seal it with caulk. Also weatherstrip the edges around the attic trapdoor or entry door.

There are often large holes around pipes (look under your sinks and behind your toilets) and ducts penetrating the walls or the attic floor. If the pipes or ducts are metal, you can fill the area around them with urethane foam. If the pipes are plastic, foam won't work well because the pipes will change size depending on their temperature. You can put insulation into a plastic garbage bag and stuff this tightly into the gap.

Other areas to seal before insulating the attic are chimney or furnace flue penetrations. Most fire codes allow sheet metal to bridge the gap between the chimney and the attic floor, and the joint between the sheet metal and the chimney can be sealed with furnace cement.

Some insulation methods actually air seal as well, and are useful for areas that are difficult to get to. For instance, dense-pack cellulose is very effective at reducing air leakage and is often used for walls and restricted ceiling cavities. Rigid board insulation and urethane foams also provide air sealing along with high R-values as insulation.

Next, seal cracks around windows and doors where you notice drafts and leaks. Windows and doors should be weatherstripped, and gaps between the framing and rough opening should be filled with caulk or foam sealant.

You may want to call a professional air sealing specialist, energy services company, or insulation contractor to seal your house. They should use air leakage detection and measuring tools, such as blower doors and infrared cameras, to help them find the biggest leaks.



Comparing Insulation Materials

There are often several types of insulation that will suit a particular job. While they all serve the same purpose, there are some differences.


The greater the R-value, the greater the insulating power. However, it is total R-value that is important. An insulation's R-value per inch is most significant when only a few inches are available--as in walls or cathedral ceilings, or in attics with very low roof slopes. Rigid foam boards have the highest R-value per inch. Fiberglass batts have higher R-values per inch than loose-fill fiberglass. Of the loose-fill insulations, cellulose and rock wool have somewhat higher R-values per inch than fiberglass.

Rigid foam and sprayed-in foams pack the most insulating capability into the thinnest area. Another advantage to using rigid insulation under wall siding is that the insulation covers the studs. In contrast, since loose-fill or batt insulation fills in between the studs, a significant part of the wall--the studs themselves--remains at only about R-3.


Cellulose tends to settle by about 20% over the first few years after installation, losing about 20% of its R-value. Therefore, manufacturers are required to state the settled thickness needed to achieve a given R-value. Initially, you need to install 20%-25% more than the settled thickness. Fiberglass and rock wool settle too, but not nearly as much.

Settling of wall insulation is particularly troublesome, because it can leave a void at the top of the wall cavity that is completely uninsulated. Settling can be avoided by blowing insulation at higher than usual density (3 1/2 lb/cubic foot for cellulose, and 1 1/2 lb/cubic foot for fiberglass). This technique is referred to as dense-pack and also helps prevent air leakage.

Weight and Density

Cellulose and rock wool are generally denser, and therefore heavier, than fiberglass. When high R-values (R-38 or more) are installed, their weight could cause some drywall ceilings to sag, but only if the ceiling is 1/2 inch drywall with framing spaced 24 inches on center--a rare combination. For most ceilings, the drywall is 5/8 inch thick or the framing is 16 inches on center, and there should be no problem with any of the insulation types.

Insulation that is installed at low density tends to lose R-value in extremely cold weather, due to natural air circulation through the insulation. This affects fiberglass loose-fill insulation blown in at typical densities of 1/2-1 lb/cubic foot, sometimes cutting its insulation capability in half. It may also occur with some new low-density cellulose loose-fills. If you live in a climate that has extremely harsh winters, use denser loose-filll products (rock wool or standard or dense-pack cellulose), blankets, or sprayed-in foam, which do not suffer from this problem.

Fire Resistance

All loose fill insulation must meet Consumer Product Safety Commission standards for fire safety. Fiberglass and rock wool are naturally fire resistant, and cellulose is treated with fire-retardant chemicals. The kraft paper or standard foil facing on some batt insulation is flammable and should not be exposed once installed. It's generally fine in attics or crawlspaces where it's installed against the ceiling or floor. Some batt facings are rated as flame resistant, and unfaced batt insulation is flammable and should not be exposed once installed. It's generally fine in attics or crawlspaces where it's installed against the ceiling or floor. Some batt facings are rated as flame resistant, and unfaced batts are available. Use rigid foam insulation in an exposed area only if it has a flame-spread index at or below 25 (the label should say FS25).

Health Considerations

Recently questions have arisen as to whether airborne glass fibers cause lung cancer. The fire-retardant chemicals, dust, and newspaper ink in cellulose also may cause irritation or health problems. If you're installing insulation yourself, avoid any such risks by using a good respiratory filter mask, as well as safety glasses, gloves, and any other protection recommended by the manufacturer.

 If you've ever handled fiberglass before, you know that skin contact can make you itch. A new type of fiberglass batt called Miraflex has curly fibers designed to be less itchy and to create less dust. Other options for the do-it-yourself installer include fiberglass batts wrapped in perforated polyethylene plastic or thin fabric, which prevent the fibers from getting onto your skin and clothing.

Environmental Concerns

Several types of insulation use recycled materials. Fiberglass is made from molten glass, usually with about 20%-30% recycled content (mostly industrial waste glass, but some manufacturers use postconsumer bottles). Cellulose is made from waste newspaper and sometimes boxes, shredded into small, fibrous particles, which are mixed with fire-retardant chemicals. Rock wool is made from industrial by-products, mainly iron ore blast furnace slag. A new cotton insulation is made from mill waste cotton and polyester.

 Urethane, styrene, and isocyanurate foams are made from petrochemicals. Some polystyrene insulation uses as much as 50% recycled resin, half of which is postconsumer plastic. Polyisocyanurate foam usually has at least 9% recycled plastic (some of it PET beverage containers).

The production of foam insulations creates some toxic pollution. Most foam insulations no longer use chlorofluorocarbons (CFCs) as blowing agents because they deplete the ozone layer. However, some still use hydrochlorofluorocarbons (HCFCs), which are less potent ozone depleters. There are several products available that use neither CFCs nor HCFCs, such as Icynene, which uses a mixture of carbon dioxide and water.

 It takes energy to save energy, at least when it comes to insulation manufacturing. Cellulose requires much less energy to produce than any other type of insulation. However, any of the insulation types should still save far more energy in your home than was used to produce it.


Publication of this article was made possible through funding from the U.S. Environmental Protection Agency and the U.S. Department of Energy's Office of Building Technologies.


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