Insulation materials

Fiberglass is the most widely used insulation material, but it's not the only type available. Each insulation material has strengths and weaknesses, and it's important to be aware of these before you choose the best home insulation for your needs.

Fiberglass is made of tiny glass fibers that can irritate the eyes, nose and throat, so you must wear protective gear when working with it. It's primarily used to make loose-fill and blanket insulation. Typical R-values are 3 to 4 per inch of thickness for loose-fill fiberglass, depending on how densely it's packed.  R-values for blanket insulation, usually batts, range from 3 to 4, depending on whether they're low-, medium- or high-density fiberglass.

Fiberglass is nonflammable, but it can absorb moisture and thus must be protected by a vapor barrier (sometimes called a vapor retardant), a sheet of foil or plastic that restricts the flow of water vapor. Fiberglass batts often have a foil or heavy Kraft paper facing as a vapor barrier.

Cellulose is pulverized paper and contains up to 75 percent recycled newsprint, so it's the greenest home-insulation material available. It is used as loose-fill insulation, mainly in walls and attics. It can settle after it's installed, which reduces its R-value. Manufacturers typically rate the settled R-value of cellulose at 3 to 4 per inch. To prevent settling or gaps, cellulose insulation is sometimes mixed with an adhesive and water and blown in damp. If installed densely enough cellulose is not air-permeable, so unlike fiberglass, it does not lose any R-value in very cold temperatures.

Cellulose is treated with nontoxic borate to make it both fire- and pest-resistant. Some experts say it should be protected by a vapor barrier, and some municipal building codes require it. Other experts say no vapor barrier is necessary if it's installed at a density of at least 2.6 pounds per cubic foot.

Polyurethane is used primarily as spray foam insulation. It is considerably more expensive than fiberglass or cellulose, but it has some advantages. For example, it forms a natural air barrier, eliminating the need for a vapor barrier, and it is an excellent choice for attic insulation. The spray expands after it is installed and seals itself to the surfaces it comes into contact with. Most experts say it should be professionally installed in larger spaces, but you can buy it in spray cans to seal around doors and windows.

There are two kinds of polyurethane foam, high density and low density. Low-density foam has an R-value of 4 per inch of thickness. It is pliant, allowing it to flex with the house's framing materials as the temperature changes. High-density polyurethane has an R-value of 7 and is fairly stiff; some rigid foam board insulation is made of this material. Polyurethane is not flammable, but it must be covered with drywall or plaster to keep toxic gases from escaping during a fire, and professional installers must wear fully-body protection and respirators when installing spray foam insulation.

Polystyrene is typically used for rigid foam board insulation, but it is also used in insulated concrete blocks and other structural insulation products, and as loose-fill insulation. There are two main types, expanded (EPS) and extruded (XPS) polystyrene, also called beadboard and blueboard, respectively. EPS is made of small plastic beads that are fused into boards, while XPS is molten material pressed into sheets. Styrofoam is an XPS.

The main difference between XPS and EPS is that XPS is more rigid, which means that it resists both moisture and compression better than EPS does. It tends to cost more also, and has a slightly higher R-value, typically 5 per inch compared to 4 to 4.5 for EPS. Polystyrene is made from petrochemicals. In the U.S., most polystyrene insulation products must be protected with a fire barrier such as gypsum wallboard or plaster.

Polyisocyanurate, or polyiso, is also used in rigid board insulation and structural insulated panels (SIPs) and other structural insulation. A low-conductivity gas in its cells gives it a high R-value, generally 6 to 8 per inch, but over time some of the gas will escape, reducing the R-value slightly. This phenomenon, known as thermal drift, usually occurs within the first two years after the insulation is installed, and from that point on the R-value is relatively stable. Plastic or foil facings are sometimes put on rigid foam panels to keep the gas from escaping.

Although polyisocyanurate is made from petrochemicals, GreenHomeGuide.com says it is environmentally preferable to other foams used for insulation, like polystyrene and polyurethane. This is because polyiso is made from at least 9 percent recycled materials, has a higher R-value than the other two types of foam and is treated with a less toxic flame retardant than polystyrene and polyurethane are.

Mineral wool insulation is available as loose-fill, blanket and rigid or semi-rigid board insulation. In the U.S. it is used mainly for commercial buildings. Because of its limited availability, it is more expensive than other types of home insulation. The term mineral wool refers to both rock wool, which is made from natural minerals like basalt, and slag wool, made from a byproduct of the steel manufacturing process. Mineral wool batts have an R-value of about 4 per inch, contain up to 90 percent recycled material and are naturally resistant to fire, moisture and insects. 

Cotton blanket insulation is made from recycled cotton denim scraps treated with a nontoxic flame retardant and pest repellent. Cotton is more expensive than fiberglass insulation, but it is not irritating to the eyes, nose and throat, which makes it much easier to work with. Cotton blanket insulation has roughly the same R-value as fiberglass, and like fiberglass, it requires a vapor barrier. Many experts consider cotton insulation a green building material since it has a high percentage of recycled content and is recyclable.

Choosing the right insulation

Insulation makes your home more energy efficient by keeping heat in during the winter and out during the summer, so your heating and air conditioning systems don't have to run as much to maintain a comfortable temperature. Here are some common questions and answers about home insulation:

What is R-value?

Insulation is designed to inhibit the flow of heat from warmer to cooler spaces. Insulation's R-value is a rating of how effectively it does this, per inch of thickness. The higher the number, the more an inch-thick layer of the insulation slows the flow of heat.

Each manufacturer rates its insulation products and lists their R-values either on the products or on their packaging. You can get the same R-value with any insulation you choose if you install enough of it. However, if you choose insulation with a high R-value you don't need as much thickness to get the same overall R-value; an inch-thick layer of R-6 insulation has the same total R-value as 2 inches of R-3 insulation. 

How much insulation is enough?

If you have an existing home, you'll first need to find out what parts of your house are and are not insulated. The Department of Energy's Energy Savers website outlines the procedure. You also can have an energy auditor do an energy assessment (sometimes called a home energy audit), or your local utility company may offer an audit free of charge. The energy audit will tell you how much insulation you currently have and pinpoint air leaks that need to be sealed, among other things. A good place to search for a qualified energy auditor is the website of the Insulation Contractors Association of America, which lists members by state.

Once you know how much insulation you already have, or if you're insulating a new home or major renovation, the next step is to determine how much insulation you need to add. In its Guide to Home Insulation, the U.S. Department of Energy recommends total R-values for different parts of the home according to what climate zone you live in. The website also recommends R-values to add to uninsulated or under-insulated attics, crawl spaces and walls.  

What is a vapor barrier?

Insulation materials that are not moisture-resistant should be protected by a sheet of foil, plastic or another water-resistant material that restricts the flow of water vapor.  This sheet is called a vapor barrier or vapor retardant. Nonmoisture-resistant insulation loses R-value when exposed to moisture, and if it absorbs and retains enough moisture, mold and rot within walls and ceilings can become a problem.  Check with an insulation product's manufacturer or a construction pro to find out whether your insulation needs a vapor barrier. If it does, experts say that the vapor barrier should face inside in cold, heating climates and outside in warm climates where cooling the house is more of an issue than heating it is.

The Department of Energy discusses vapor barriers and their use as part of a moisture-control strategy for your home on their website.

What types of insulation are best for an existing home? 

If you're adding insulation to your current home, the best type to use depends on where you'll be installing it.

  • Walls: If you're retrofitting existing walls, you can rule out blanket insulation and rigid foam boards, which can't be installed in enclosed spaces. Choose between loose-fill and spray foam, either of which can be blown into the space through small holes that are then filled. Loose-fill is less expensive, and you can install it yourself, although you'll need to rent a machine to do it. Spray foam must be professionally installed, but it doesn't require a vapor barrier, while some building codes may require a vapor barrier with cellulose.
  • Attic floors: Either loose-fill or blanket insulation is typically used for attic floors, whether for retrofits or new construction. Blanket insulation comes in widths sized to fit standard spacing between wall studs and floor and ceiling joists, usually 16 and 24 inches wide, and most experts say installing it is a fairly easy DIY project. Loose-fill may be easier to blow in on top of an existing layer of insulation. Spray foam insulation may be used if there is no existing insulation.
  • Basement and foundation walls: Rigid foam board insulation made of extruded polystyrene is moisture resistant enough to be used below grade on exterior foundation walls. A Washington Post article by Ask the Builder's Tim Carter explains how to install it correctly. Rigid foam board insulation is also a good choice for unfinished basement walls and ceilings. Blanket or spray foam insulation may also be used.

Tax breaks for installing home insulation

The federal government offers incentives for purchasing energy-efficient products for your home. For the 2011 tax year, you can claim a tax credit of 10 percent of the cost of an "insulation material or system specifically and primarily designed to reduce the heat loss or gain of your home" up to $500. You can claim it only for your primary residence, and the cost does not include installation or labor. 

Many states offer financial incentives as well. To determine what your state may offer, check the Database of State Incentives for Renewables and Efficiency. Some local governments offer incentives as well.

Insulation materials

Fiberglass is the most widely used insulation material, but it's not the only type available. Each insulation material has strengths and weaknesses, and it's important to be aware of these before you choose the best home insulation for your needs.

Fiberglass is made of tiny glass fibers that can irritate the eyes, nose and throat, so you must wear protective gear when working with it. It's primarily used to make loose-fill and blanket insulation. Typical R-values are 3 to 4 per inch of thickness for loose-fill fiberglass, depending on how densely it's packed.  R-values for blanket insulation, usually batts, range from 3 to 4, depending on whether they're low-, medium- or high-density fiberglass.

Fiberglass is nonflammable, but it can absorb moisture and thus must be protected by a vapor barrier (sometimes called a vapor retardant), a sheet of foil or plastic that restricts the flow of water vapor. Fiberglass batts often have a foil or heavy Kraft paper facing as a vapor barrier.

Cellulose is pulverized paper and contains up to 75 percent recycled newsprint, so it's the greenest home-insulation material available. It is used as loose-fill insulation, mainly in walls and attics. It can settle after it's installed, which reduces its R-value. Manufacturers typically rate the settled R-value of cellulose at 3 to 4 per inch. To prevent settling or gaps, cellulose insulation is sometimes mixed with an adhesive and water and blown in damp. If installed densely enough cellulose is not air-permeable, so unlike fiberglass, it does not lose any R-value in very cold temperatures.

Cellulose is treated with nontoxic borate to make it both fire- and pest-resistant. Some experts say it should be protected by a vapor barrier, and some municipal building codes require it. Other experts say no vapor barrier is necessary if it's installed at a density of at least 2.6 pounds per cubic foot.

Polyurethane is used primarily as spray foam insulation. It is considerably more expensive than fiberglass or cellulose, but it has some advantages. For example, it forms a natural air barrier, eliminating the need for a vapor barrier, and it is an excellent choice for attic insulation. The spray expands after it is installed and seals itself to the surfaces it comes into contact with. Most experts say it should be professionally installed in larger spaces, but you can buy it in spray cans to seal around doors and windows.

There are two kinds of polyurethane foam, high density and low density. Low-density foam has an R-value of 4 per inch of thickness. It is pliant, allowing it to flex with the house's framing materials as the temperature changes. High-density polyurethane has an R-value of 7 and is fairly stiff; some rigid foam board insulation is made of this material. Polyurethane is not flammable, but it must be covered with drywall or plaster to keep toxic gases from escaping during a fire, and professional installers must wear fully-body protection and respirators when installing spray foam insulation.

Polystyrene is typically used for rigid foam board insulation, but it is also used in insulated concrete blocks and other structural insulation products, and as loose-fill insulation. There are two main types, expanded (EPS) and extruded (XPS) polystyrene, also called beadboard and blueboard, respectively. EPS is made of small plastic beads that are fused into boards, while XPS is molten material pressed into sheets. Styrofoam is an XPS.

The main difference between XPS and EPS is that XPS is more rigid, which means that it resists both moisture and compression better than EPS does. It tends to cost more also, and has a slightly higher R-value, typically 5 per inch compared to 4 to 4.5 for EPS. Polystyrene is made from petrochemicals. In the U.S., most polystyrene insulation products must be protected with a fire barrier such as gypsum wallboard or plaster.

Polyisocyanurate, or polyiso, is also used in rigid board insulation and structural insulated panels (SIPs) and other structural insulation. A low-conductivity gas in its cells gives it a high R-value, generally 6 to 8 per inch, but over time some of the gas will escape, reducing the R-value slightly. This phenomenon, known as thermal drift, usually occurs within the first two years after the insulation is installed, and from that point on the R-value is relatively stable. Plastic or foil facings are sometimes put on rigid foam panels to keep the gas from escaping.

Although polyisocyanurate is made from petrochemicals, GreenHomeGuide.com says it is environmentally preferable to other foams used for insulation, like polystyrene and polyurethane. This is because polyiso is made from at least 9 percent recycled materials, has a higher R-value than the other two types of foam and is treated with a less toxic flame retardant than polystyrene and polyurethane are.

Mineral wool insulation is available as loose-fill, blanket and rigid or semi-rigid board insulation. In the U.S. it is used mainly for commercial buildings. Because of its limited availability, it is more expensive than other types of home insulation. The term mineral wool refers to both rock wool, which is made from natural minerals like basalt, and slag wool, made from a byproduct of the steel manufacturing process. Mineral wool batts have an R-value of about 4 per inch, contain up to 90 percent recycled material and are naturally resistant to fire, moisture and insects. 

Cotton blanket insulation is made from recycled cotton denim scraps treated with a nontoxic flame retardant and pest repellent. Cotton is more expensive than fiberglass insulation, but it is not irritating to the eyes, nose and throat, which makes it much easier to work with. Cotton blanket insulation has roughly the same R-value as fiberglass, and like fiberglass, it requires a vapor barrier. Many experts consider cotton insulation a green building material since it has a high percentage of recycled content and is recyclable.

Choosing the right insulation

Insulation makes your home more energy efficient by keeping heat in during the winter and out during the summer, so your heating and air conditioning systems don't have to run as much to maintain a comfortable temperature. Here are some common questions and answers about home insulation:

What is R-value?

Insulation is designed to inhibit the flow of heat from warmer to cooler spaces. Insulation's R-value is a rating of how effectively it does this, per inch of thickness. The higher the number, the more an inch-thick layer of the insulation slows the flow of heat.

Each manufacturer rates its insulation products and lists their R-values either on the products or on their packaging. You can get the same R-value with any insulation you choose if you install enough of it. However, if you choose insulation with a high R-value you don't need as much thickness to get the same overall R-value; an inch-thick layer of R-6 insulation has the same total R-value as 2 inches of R-3 insulation. 

How much insulation is enough?

If you have an existing home, you'll first need to find out what parts of your house are and are not insulated. The Department of Energy's Energy Savers website outlines the procedure. You also can have an energy auditor do an energy assessment (sometimes called a home energy audit), or your local utility company may offer an audit free of charge. The energy audit will tell you how much insulation you currently have and pinpoint air leaks that need to be sealed, among other things. A good place to search for a qualified energy auditor is the website of the Insulation Contractors Association of America, which lists members by state.

Once you know how much insulation you already have, or if you're insulating a new home or major renovation, the next step is to determine how much insulation you need to add. In its Guide to Home Insulation, the U.S. Department of Energy recommends total R-values for different parts of the home according to what climate zone you live in. The website also recommends R-values to add to uninsulated or under-insulated attics, crawl spaces and walls.  

What is a vapor barrier?

Insulation materials that are not moisture-resistant should be protected by a sheet of foil, plastic or another water-resistant material that restricts the flow of water vapor.  This sheet is called a vapor barrier or vapor retardant. Nonmoisture-resistant insulation loses R-value when exposed to moisture, and if it absorbs and retains enough moisture, mold and rot within walls and ceilings can become a problem.  Check with an insulation product's manufacturer or a construction pro to find out whether your insulation needs a vapor barrier. If it does, experts say that the vapor barrier should face inside in cold, heating climates and outside in warm climates where cooling the house is more of an issue than heating it is.

The Department of Energy discusses vapor barriers and their use as part of a moisture-control strategy for your home on their website.

What types of insulation are best for an existing home? 

If you're adding insulation to your current home, the best type to use depends on where you'll be installing it.

  • Walls: If you're retrofitting existing walls, you can rule out blanket insulation and rigid foam boards, which can't be installed in enclosed spaces. Choose between loose-fill and spray foam, either of which can be blown into the space through small holes that are then filled. Loose-fill is less expensive, and you can install it yourself, although you'll need to rent a machine to do it. Spray foam must be professionally installed, but it doesn't require a vapor barrier, while some building codes may require a vapor barrier with cellulose.
  • Attic floors: Either loose-fill or blanket insulation is typically used for attic floors, whether for retrofits or new construction. Blanket insulation comes in widths sized to fit standard spacing between wall studs and floor and ceiling joists, usually 16 and 24 inches wide, and most experts say installing it is a fairly easy DIY project. Loose-fill may be easier to blow in on top of an existing layer of insulation. Spray foam insulation may be used if there is no existing insulation.
  • Basement and foundation walls: Rigid foam board insulation made of extruded polystyrene is moisture resistant enough to be used below grade on exterior foundation walls. A Washington Post article by Ask the Builder's Tim Carter explains how to install it correctly. Rigid foam board insulation is also a good choice for unfinished basement walls and ceilings. Blanket or spray foam insulation may also be used.

Tax breaks for installing home insulation

The federal government offers incentives for purchasing energy-efficient products for your home. For the 2011 tax year, you can claim a tax credit of 10 percent of the cost of an "insulation material or system specifically and primarily designed to reduce the heat loss or gain of your home" up to $500. You can claim it only for your primary residence, and the cost does not include installation or labor. 

Many states offer financial incentives as well. To determine what your state may offer, check the Database of State Incentives for Renewables and Efficiency. Some local governments offer incentives as well.

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