Types of Insulation

 

When it comes to insulating your home, there is a variety of options from which to choose. To select the best type for you, consider the area you want to insulate and which R-value—the material’s resistance to heat flow—is recommended to achieve the best results.

Batts & Blankets

Insulation batts and blankets are made of glass fiber or mineral wool (along with other synthetic fibers) and are most commonly used in new construction or unconfined areas, like unfinished attics, roofs, and under floors. Blankets come in rolls of up to 64 feet.

Batts are simply blankets pre-cut into 4-foot or 8-foot lengths. Widths are standard 16 inches or 24 inches, making these forms of insulation best for wood framing that uses the same dimensions between studs. Thicknesses include 3 inches, 6 inches and 9 inches, but a 1-inch version is available for special applications, like around sills and narrow spaces inside masonry walls. The R-value for each of these thicknesses varies with the material.

The choice between batts or blankets balances convenience against costs. Blankets are clumsy to install, but if many batts must be trimmed to fit, greater waste results. Batts or blankets are available faced or unfaced, meaning they come with or without backing materials made of foil or paper. Backing materials can serve as vapor barriers. Foil backing works well as a vapor barrier, paper not as well unless it has been treated to reduce moisture permeability.


Cellulose

Cellulose insulation is made from paper products, primarily recycled newsprint. The paper is shredded and milled to produce a fluffy, low-density material. Large amounts of chemicals, primarily boric acid, are added to provide flame resistance. The great advantages of cellulose are its relative low cost, ease of installation and high R per inch, roughly 25% higher than glass fiber. Its disadvantages are it can absorb moisture, which may alter its physical and chemical properties, and it may settle if not applied at the correct density.


Composite Insulating Panels

Composite insulation panels include structural insulating panels (SIP) and insulated roof panels. Structural insulated panels, “insulated sandwich panels,” or “stress(ed)-skin panels,” consist of an insulated core sheathed on two sides.

The insulation is usually a foam-based plastic such as polystyrene or isocyanurate, but foam-straw composites are occasionally available. Sheathing materials include plywood, oriented strand board (OSB), and waferboard; interior sheathing materials also include drywall. The panels range in size, but are most common in 4 « 8 and 4 « 9 foot (1.2 « 2.4 and 1.2 « 2.7 meter) varieties.

Because of its integral strength, composite panel systems reduce the need for structural lumber, opportunities for air leaks, and job site assembly time. A comparison of stick-built and panel-built test houses shows a slight energy saving with structural panel construction. Because these panels also reduce sound transmission, some professionals use them for interior partitions.

Insulated roof panels have a nailable sheathing layer over an insulation base, typically rigid foam. Use this product only where you need sheathing on one side–for example, a retrofit application over an existing sheathed roof. These panels are very effective at increasing the R-value of a roof. Scandinavians have used this type of application for years to help prevent condensation inside attics. The insulated roof panels are also available with air channels just under the exterior sheathing for ventilated roof designs.


Cotton

Cotton thermal insulation is available as batt or loose fill. It consists of recycled cotton, polyester and nylon fibers, and is treated with a flame retardant and insect/rodent repellents. It meets the same Class I standards for fire resistance as fiberglass insulation. The batts come in standard widths, thicknesses and R-values with a Kraft paper facing on one side. Unlike conventional fiberglass insulation, cotton insulation does not irritate the skin when being installed. Cotton insulation is not yet readily available in all sections of the country. Check with a participating contractors for ordering information.


Foam Insulation

Foam insulation, usually composed of urethane, can be injected into wall cavities or sprayed onto roof or floors. Once applied, it expands and sets in about a minute. After it sets, it shrinks slowly for several weeks. Properly applied, shrinkage is less than 5%. Like rigid boards, foam insulation has the advantage of high R per inch. Similarly, it shares the disadvantage of requiring a fireproof covering material when installed inside the home.


Glass Fiber (Fiberglass)

Glass fiber, best known by its trade name fiberglass, is one of the most common insulation materials and is standard in newly constructed wood-frame homes. It is made of long, spun glass fibers coated with resins to create bonding between the fibers.

Fiberglass has the advantages of being relatively inexpensive, easy to install, resistant to moisture damage while being relatively nonflammable. In batt or blanket form, it has the advantage of not settling and creating gaps after installation. In its rigid board form, it offers the advantages of high R per inch and some structural stability.

Glass fibers can be irritating; therefore, installing it requires some special handling. Masks, gloves, long sleeves and other protective apparel should be worn when handling this type of insulation.


Loose-Fill

Blown-in loose fill is one of the easiest forms of insulation to install. Commonly made of cellulose, glass fiber or mineral wool, it can be blown into areas needing insulation. Equipment for blowing insulation into walls or attics can be rented, or contractors with their own equipment can be hired to do the job.

To ensure getting the maximum R-value from the insulating material, watch the density setting used. Properly blown loose fill generally has a higher insulating value per inch than poured loose fill because of the loft added by blowing. As with all insulation types, vapor barriers are often needed.

A new and increasingly popular form of this insulation involves blowing glass or wool fibers mixed with an adhesive into building cavities. The resulting installation cures in a few days, is resistant to settling, and provides effective sealing of the cavities.

Types of Loose-Fill

Poured

Loose fill is perhaps the easiest form of insulation to install. Commonly made of cellulose, glass fiber or mineral wool, it comes in bags that can be poured into areas needing insulation. For unfinished attics, the material can be poured between joists and spread with a rake. Loose fill pours easily into cavities that are difficult to fill with batts or rigid insulation.

Loose fill has the disadvantage that over time, it can settle. This is particularly a problem in vertical cavities such as walls. Taking care to install it at the proper density minimizes this problem. As with all insulation types, vapor barriers are often needed.


Mineral Wool

Mineral wool, also known as rock or slaq wool, is similar to glass fiber insulation except the raw material is steel, copper or lead slags, or naturally occurring rock rather than glass. Mineral wool’s insulating ability is about 10% greater than that of fiberglass. Since mineral wools are made from rock or slag melted at temperatures over 219°F, the base material of batt or blowing wool is non-combustible. However, binders added to them may be flammable. Mineral wools can be irritating; therefore, masks, gloves, long sleeves and other protective apparel should be worn when handling this type of insulation.


Polystyrene Insulation

This molded synthetic is an excellent insulator, but is somewhat expensive and flammable. It is manufactured in two ways: one is extrusion, which results in fine, closed cells, containing a mixture of air and refrigerant gas. The other is molded or expanded, which produces coarse, closed cells containing air.

Commonly called beadboard, molded or expanded polystyrene has a lower R-value than extruded polystyrene because it is less dense and does not contain refrigerant gas. It is also less expensive than the extruded form.

Both types of polystyrene insulation have the advantages of high R-value, good moisture resistance, and high structural strength compared to other rigid insulation materials. They are easy to work with and can be used as sheathing. The disadvantages are they can be expensive, are flammable (meaning they require a fire-protective covering), and can degrade when exposed to sunlight or temperatures over 165°F.


Reflective Insulation

Reflective or radiant barrier insulation dates back to the 1930s. It is a potentially inexpensive way to protect a building from undesirable heat gain. Reflective insulation differs from other insulating materials in the manner in which it retards heat transfer. Unlike the others, it works by reflecting incident infrared radiation, thus reducing radiant heat transfer.

Reflective insulation is fabricated from aluminum foil with backings applied to provide a series of closed air spaces. Its insulating value is derived from the heat-reflective surfaces separated by air spaces into which the radiation is reflected. Studies show it is more effective in keeping heat out of homes in hot climates than keeping heat in homes in cold ones. It is typically installed between roof rafters, floor joists or wall studs. The R-value depends on the heat flow direction and is most effective in reducing downward heat flow. Single foil radiant barriers placed in attics reduce heat transfer from roofs.


Rigid Boards

Rigid boards are plastic foams or fibrous materials pressed or extruded into board-like forms. Common materials include polystyrene, urethane or glass fiber.

Polystyrene and urethane have superior insulating qualities, and would therefore be a better choice than batts or blankets if it were not for their flammability. When installed inside a house, the boards require an additional covering of a minimum of 1/2-inch-thick fireproof material, such as gypsum wall board. Rigid board has the advantages of structural strength, low weight and high R per inch. To achieve an R-30 using glass fiber blankets would require roughly 8.5 inches. With rigid urethane boards, R-30 can be attained with only 5.5 inches. Rigid boards come faced and unfaced. Some are faced with a reflective material that acts as a vapor barrier and reduces heat flow when facing a dead air space.


Urethane Insulation

Urethane insulation is made of plastic polymers and features 80-90% closed cells containing refrigerant gas rather than air. It is one of the most effective insulators, but is flammable. When it burns it emits cyanide gas and is therefore banned in some areas of the country.


Vermiculite/Perlite Insulation

Vermiculite is a mica-like laminar material; perlite, a naturally occurring volcanic glass. Both are heat-expanded materials often used by gardeners as planting media. Because they are inexpensive insulators, they are useful as home insulation. Besides their relatively low cost, other advantages include being easy to install because they pour to fill irregular spaces. They are also non-corrosive, non-combustible and vermin resistant.