Properly insulated homes can use 30 to 50 less energy than homes without insulation. Lining your "thermal envelope" - adding materials that don't readily allow heat to leak through your walls, ceilings, floors, from around your home's foundations and its ductwork - saves energy by keeping heat in during the winter and keeping heat out during the summer. Unless you live were you never need to use heating or air conditioning, insulation needs to be an important part of your home. Think of it like putting a sweater on your home in the winter.

The best insulation options depend on the choices you've made in other construction materials. Steel studs, for example, conduct heat much more readily than do wood studs. To compensate for this tendency, steel studs should be covered with an insulating sheathing, minimizing the thermal bridging effect. The same technique need not be used for a wood-framed house.

The effectiveness of a piece of insulation is measured by its R-value. The R-value in insulation designates its resistance to heat flow. The higher the R-value, the greater the insulating ability - the more effective it is. Generally speaking, each time you double the R-value of insulation, you cut your conduction heat loss in that area in half. Adding insulation to an uninsulated attic is the most cost-effective, energy-saving measure you can do. Most older houses were built with little or no insulation. In more moderate climates, the minimum recommended R-value is R-30 for an attic, R-11 for walls, R-19 for raised floors, and R-4.2 for ductwork.

Putting It In Place

You can greatly increase the energy efficiency and comfort of a home by installing insulation with an R-value higher than the minimum requirements. But to truly enjoy the benefits of insulation, it must be installed correctly. Compressing it or leaving gaps through which air can flow can cut insulation's effectiveness in half. When insulating your attic, it's important not to clog the attic vents under the eaves. Keep air circulating freely above the insulation by installing baffles (typically a piece of fiberglass batt placed several inches away from the vent). For fire safety, keep insulation clear of heat producing devices such as doorbell transformers and recessed lights, flues or vents from furnaces, water heaters, fireplaces, and exhaust fans.

Places to Insulate

  1. In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below. (1A) attic access door
  2. In finished attic rooms with or without dormer, insulate (2A) between the studs of "knee" walls, (2B) between the studs and rafters of exterior walls and roof, (2C) and ceilings with cold spaces above. (2D) Extend insulation into joist space to reduce air flows.
  3. All exterior walls, including (3A) walls between living spaces and unheated garages, shed roofs, or storage areas; (3B) foundation walls above ground level; (3C) foundation walls in heated basements, full wall either interior or exterior.
  4. Floors above cold spaces, such as vented crawl spaces and unheated garages. Also insulate (4A) any portion of the floor in a room that is cantilevered beyond the exterior wall below; (4B) slab floors built directly on the ground; (4C) as an alternative to floor insulation, foundation walls of unvented crawl spaces. (4D) Extend insulation into joist space to reduce air flows.
  5. Band joists.
  6. Replacement or storm windows and caulk and seal around all windows and doors.

Source: Oak Ridge National Laboratory

The Department of Energy has additional information.

Types of Insulation

There are four basic types of insulation:

  • loose fill
  • batts and blankets
  • rigid board
  • spray foam

Each type has benefits that make it better for insulating different parts of your house, depending on the type of construction. Some types are easier to use for remodeling - foam can be installed through a hole in the wall without removing wall board, for example.

Loose-fill Insulation

Loose-fill insulation can be blown into building cavities or attics using special equipment. It generally costs more than batt insulation, but can fill gaps and corners well. This reduces air leakage, and provides better sound insulation. Loose-fill insulation typically has a value of approximately R-3 to R-4 per inch.

Batt and Blanket Insulation

Batt or blanket insulation is used to insulate below floors, above ceilings, and within walls. Made of fiberglass or rock wool, batts typically come in lengths of 4 or 8 feet. Blankets come in long rolls that can be cut to the desired length. Both batts and blankets typically have an R-value of approximately R-3 per inch of thickness. It is usually 16 or 24 inches wide, the size between standard joists, rafters, or studs in most homes. Batt insulation is the least expensive wall insulation material but requires careful installation to be effective.

Rigid Board Insulation

Rigid board insulation can be made from fiberglass, polystyrene, or polyurethane, and comes in a variety of thicknesses. It typically is used to insulate flat roofs or cathedral ceilings, basement walls and the edges of concrete slabs. It offers a high insulating rating - approximately R-4 to R-8 per inch.

Spray Foam Insulation

Spray foam insulation is made from combining a containing a polymer such as polyurethane or modified urethane and a foaming agent. The resulting liquid is sprayed through a nozzle into wall, ceiling, and floor cavities where it expands and hardens into a solid plastic mass of small air-filled cells. Commonly used for remodels and retrofits, spray foam effectively fill gaps and holes and forms a good air and moisture barrier. Spray foam insulation, which needs to be applied by a professional using special equipment. It typically has an aged R-value of approximately R-6 per inch.

Insulation is made from various materials:

Fiberglass insulation available as blanket-like batts is the industry standard. It's actually glass, spun into long fibers, then woven and coated with a binding agent. Frequently made with 30 percent or more post-consumer recycled glass, fiberglass also comes as loose-fill and as rigid boards. Fiberglass batt insulation is popular because it's relatively easy to install, and batts are manufactured to fit the standard spaces between studs. Fiberglass is resistant to both fire and mold and small amounts of moisture have little effect on its R-value. The characteristics of fiberglass that make it popular can also be drawbacks. Batts of insulation designed for normal-sized cavities do not readily fit into irregular spaces. That can result in uninsulated spaces if installation isn't done carefully. Air movement around the insulation can significantly reduce its R-value.

Mineral-fiber insulation includes slag wool, which is made from blast furnace slag (the scum that forms on the surface of molten metal) that is spun into fibers. The fibers, treated with oil and binders to suppress dust and maintain the material's shape, can be woven into batts. A second type of mineral-fiber insulation called rock wool is manufactured in a similar way using natural basalt or diabase rock instead of slag.

Mineral-fiber insulation looks, feels and performs much like fiberglass. It, too, is sold as batts, loose-fill and rigid boards, and has the same benefits and drawbacks as fiberglass insulation. Since it doesn't melt or support combustion, it is a good material for insulating around chimneys.

Vermiculite is a mineral closely related to mica. When heated, it expands to form a lightweight material with insulating properties. Both treated and untreated vermiculite are used as insulation. Untreated vermiculite readily absorbs water and dries very slowly. The treated material is coated with asphalt to make it water-repellent for use in high moisture areas. Both types of vermiculite are usually installed by hand, a simple process. It is non-combustible, odorless and non-irritating. It doesn't offer as high an R-value as other types of insulation, however. Because it can contain asbestos, it is less common today and is found mostly in homes built before 1950.

Cellulose thermal insulation is made from recycled paper products, primarily finely shredded newsprint that is chemically treated to resist fire, corrosion, vermin and fungal growth. It generally contains approximately 85 percent recycled paper. Only available in loose-fill form, it is either poured in place or installed with a blower. Because of the small size of the particles, cellulose can 'flow' around obstructions such as nails, electrical wires, trusses and braces to fill cavities uniformly. One drawback of insulating with cellulose is that it can settle over time if the insulation is not blown or poured to manufacturer's recommended density.

Rigid foam insulation is applied directly to framing as rigid sheets. Several types of foam are available, some with post consumer recycled content made from reclaimed fast-food containers and cups.

Rigid foam is the insulation of choice where space is very limited but a high R-value is needed. It can be installed on the interior or exterior of a wall, but on the inside it must be covered by a fire-resistant material like wallboard. When the joints between panels are properly sealed, rigid foam insulation can act as both an air and vapor barrier.

"Expanded" types of rigid foam insulation are CFC-free; they are now manufactured with a non-chlorofluorocarbon (CFC) gas. "Extruded" types, which offer higher performance, originally were made with CFCs before manufacturers switched to using hydrochlorofluorocarbons (HCFCs), substances with far less potential to deplete the Earth's fragile ozone layer. While new extruded products that don't even contain HCFCs will soon become available, they contain chemicals that are still being evaluated to see what their effect will be on global warming. One drawback to most foam insulation is that it deteriorates unless it is protected from prolonged exposure to sunlight and water. It also tends to be more expensive than most other types of insulation.

Polyurethane foams are also high-performance insulating materials available as rigid boards or sprayed-in-place material. Sprayed or foamed-in-place polyurethane insulation is usually cheaper than the foam boards, and usually perform better because the liquid foam molds itself to all of the surfaces, sealing holes and filling gaps. All closed-cell polyurethane foam insulation made today is produced with a non-HCFC (hydrochlorofluorocarbon) gas as the foaming agent.

Low-density, open-cell polyurethane foams use air as the blowing agent and provide a steady R-factor of about R-3.6 per inch. Some low-density varieties use carbon dioxide (CO2) as the foaming agent.

Low-density foams are sprayed into open wall cavities and rapidly expand to seal and fill the cavity. Slow expanding foam is also available, which is intended for cavities in existing homes. The liquid foam expands very slowly, reducing the chance of damaging the wall from overexpansion.

Soy-based, polyurethane liquid spray-foam products are also available. The cured R-value is about R-3.5 per inch. These products can be applied with the same equipment used for petroleum-based polyurethane foam products.

Natural Fiber Insulation, Insulation made from natural fibers such as cotton, sheep's wool, straw, and hemp is becoming increasingly popular.

Cotton insulation is made up of 85 percent recycled cotton and 15 percent plastic fibers that have been treated with borate, the same flame retardant and insect-and-rodent repellent used in cellulose insulation. Perhaps you have heard of the product that uses recycled trimmings and waste from manufacturing blue jeans. As a result of its recycled content, blue jeans insulation uses minimal energy to manufacture.

Cotton insulation is available in batts with an R-value of R-3.4 per inch. It is nontoxic and can be installed without using respiratory or skin exposure protection. However, cotton insulation costs about 15 percent to 20 percent more than fiberglass batt insulation.

Sheep's wool insulation is also treated with borate to resist pests, fire, and mold. It can hold large quantities of water, which is an advantage for use in some walls, but repeated wetting and drying can leach out the borate. The thermal resistance or R-value of sheep's wool batts is about R-3.5 per inch, similar to other fibrous insulation types.

Straw bale construction, a popular way to construct well-insulated walls 150 years ago on the Great Plains, is becoming popular again. Thick straw bales are stacked like bricks to provide insulation.

Straw can also be fused into insulating boards without adhesives, a process developed in the 1930s. Panels are usually 2 to 4 inches thick and are faced with heavyweight kraft paper on each side. Although manufacturers claims vary, R-values realistically range from about R-1.4 to R-2 per inch. The boards also make effective sound-absorbing panels for interior partitions. Some manufacturers have developed structural insulated panels built from multi-layered, compressed-straw panels.

Hemp insulation is relatively unknown and not commonly used in the United States, mainly because it comes from varieties of the Cannabis plant that farmers are prohibited from growing. But hemp and flax fibers can be an environmentally sustainable alternative to conventional insulation, offering comparable or better thermal and acoustic performance with all the environmental benefits of a natural product.