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Home Insulation

Inadequate insulation and air leakage are leading causes of energy waste in most homes. Added insulation can make your house more comfortable by helping to maintain a uniform temperature throughout the house. Insulation can also act as a sound absorber or barrier, keeping noise levels down. Adding insulation in the attic, walls, floors, basements, and crawl spaces may be the best way to improve your home's energy efficiency.
Check the insulation in your attic, ceilings, exterior and basement walls, floors and crawl spaces to see if it meets the levels recommended for your area. Insulation is measured in R-values—the higher the R-value, the better your walls and roofs will resist the transfer of heat.

The easiest and most cost-effective way to insulate your home is to add insulation in the attic. To find out if you have enough attic insulation, measure the thickness of insulation. If there is less than R-19 (6 inches of fiber glass or rock wool or 5 inches of cellulose) you could probably benefit by adding more.

Insulation usually comes in four types—batts, rolls, loose-fill and rigid foam boards. Each type is made to fit in a different part of your home.

Insulation priorities

  • Insulate your attic to the recommended level, including the attic door or hatch cover.
  • Provide the recommended level on insulation under floors above unheated spaces, around walls in a heated basement or unventilated crawl space, and on the edges of slab-on-grade foundations. Use the recommended levels of insulation for exterior walls for new house construction. When remodeling or re-siding your house, consider using the levels recommended for new construction in your existing walls.

Insulation Tips

  • Consider factors such as your climate, building design and budget when selecting insulation R-value for your home.
  • Use higher density insulation, such as rigid foam boards in cathedral ceilings and on exterior walls.
  • Ventilation plays a large role in providing moisture control and reducing summer cooling bills. Install attic vents to help make sure that there is one inch of ventilation space between the insulation and roof shingles. Attic vents can be installed along the entire ceiling cavity to help ensure proper airflow from the soffit to the attic, helping to make a home more comfortable and energy efficient.
  • Do not block vents with insulation, and keep insulation at least 3 inches away from recessed lighting fixtures or other heat-producing equipment unless it is marked "I.C"—designed for direct insulation contact.
  • These recommendations are based on the assumption that no structural modifications are needed to accommodate the added insulation.

The R-value of a wall is a measurement of its thermal resistance.

Many homes are still built using the traditional standard of 2 by 4 walls and R-11 fiberglass batt insulation. But most builders don't consider this old standard to be adequate. Insulation dealers now sell enhanced batts for 2-by-4 walls that are rated at R-13 or R-15.

The effectiveness of insulation is measured in R-value per inch. The total R-value of your insulation depends both on its type and its depth. To determine the total R-value of your insulation, decide what type of insulation is installed, and multiply the R-value per inch times the number of inches installed. Cellulose loose-fill insulation, for example, is rated at about R-3.5 per inch. If your attic has 4 inches of cellulose, that's 3.5 x 4 = R-14. Your attic insulation should be R-30. In cold winter climates many attics are insulated to at least R-40.

The U.S. Dept. of Energy makes R-value recommendations for different areas of the country. The Zip Code Insulation program can tell you the most economic insulation level for your new or existing home.

Batts have a heavy paper backing on one side and a pink, fibrous material—usually made of either fiber glass or rock wool—on the other. Batts are simply blankets pre-cut into 4 ft. or 8 ft. lengths. Widths are standard 16 in. or 24 in. Batts are made to fit between the studs in your walls or between the joists of your ceilings or floors.

Rolls or blankets are usually made of fiber glass and can be laid over the floor in the attic.

Loose-fill insulation, usually made of fiber glass, rock wool or cellulose, is blown into the attic or walls.

Rigid Foam Boards
Rigid foam boards are made of extruded polystyrene, expanded polystyrene or other materials. These boards are lightweight, provide structural support and generally have an R-value of 4 to7 per inch. Rigid board insulation is made to be used in confined spaces such as exterior walls, basements, foundation and stem walls, concrete slabs and cathedral ceilings

Slab-on-grade floors are often the least expensive foundation system. It consists of a concrete slab poured over at least four inches of gravel and a layer of polyethylene. Homes use slab-on-grade floors in two ways: Either as the bottom floor in a home, or the floor in a daylight basement where the floor level is about even with the outside earth. Areas with mild winters do not require a deep foundation. In these regions, slab-on-grade foundations may provide an ideal choice for flat lots. In most sections of the country, insulating the exterior edge of the slab can reduce winter heating bills by 10 to 20 percent.


U.S. Department of Energy, Energy Efficiency and Renewable Energy

James Dulley, House Insulation Guide

John Krigger, Saturn Resource Management. Author of numerous energy efficiency books including Surviving the Seasons and Residential Energy: Cost Savings and Comfort for Existing Buildings

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