How Does Insulation Work For You?

Heat flows naturally from a warmer to a cooler space. In the winter, this heat flow moves directly from all heated living spaces to adjacent unheated attics, garages, and basements, or to the outdoors; or indirectly through interior ceilings, walls, and floors--wherever there is a difference in temperature. During the cooling season, heat flows from outdoors to the house interior. To maintain comfort, the heat lost in winter must be replaced by your heating system and the heat gained in summer must be removed by your air-conditioner. Insulating ceilings, walls, and floors decreases this heat flow by providing an effective resistance to the flow of heat.

Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness and resistance to heat flow. Typically, higher R-values are recommended for ceilings than for walls and floors. Although your local building codes should specify R-values for homes, these building codes often represent a minimum  level of insulation necessary for comfort, rather than a level recommended for optimal  energy efficiency. To find the optimum levels recommended by DOE for your general location, check the Energy Savers R-Value map in this section. The R-value of thermal insulation depends on the type of material, its thickness, and density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added. Installing more insulation in your home increases R-value and the resistance to heat flow

The effectiveness of an insulated wall or ceiling also depends on how and where the insulation is installed. For example, insulation which is compressed will not give you its full rated R-value. Also, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists. That is, the overall R-value of a wall with insulation between wood studs is less than the R-value of the insulation itself because the wood provides a thermal short-circuit around the insulation. The short-circuiting through metal framing is much greater than that through wood-framed walls; sometimes the metal wall's overall R-value can be as low as half the insulation's R-value. With careful design, this short-circuiting can be reduced. More information can be found on the Web about whole-wall R-values.

Insulation is available in a variety of forms, including batts and blankets, rigid board, and loose fill. Each type is made to fit in a different part of your house. Batts, usually made of fiberglass or  Rockwool, are made to fit between the studs in your walls or between the joists of your ceilings or floors Rolls or blankets, also usually made of fiberglass, can be laid over the floor in the attic. Loose-fill insulation, usually made of fiberglass,  Rockwool or cellulose, can either be poured in or blown in to spaces. Rigid foam boards are made of polyisocyanurate, extruded polystyrene (XPS or blueboard), expanded polystyrene (EPS or beadboard), or other materials. These boards are lightweight, provide structural support, and generally have an R-value of 4 to 7 per inch.

When adding insulation to your home, you will probably use batts or blankets on attic floors, to insulate first-story floors from crawl spaces or unheated basements, or to insulate exterior walls. Rigid boards can be added to basement walls, exposed foundations, cathedral ceilings, and exterior walls. If you are removing the plasterboard from exterior walls (or adding new walls), you should consider using rigid board insulation in exterior walls. Both types of insulation-batts and rigid boards-can be used to insulate the access openings to attic spaces.

Loose-fill insulation can be blown or poured into existing walls or attics. Loose-fill insulations require less energy to produce than other forms of insulation, and cellulose loose-fill insulation is made from recycled materials.

  • Should I insulate my home? The answer is probably "yes" if you:

  • Have an older home and haven't added insulation: in a recent survey, only 20% of homes built before 1980 were well insulated;

  • Are uncomfortably cold in the winter or hot in the summer-adding insulation creates a more uniform temperature and increases comfort;

  • Build a new house or addition, or install new siding or roofing;

  • Pay excessive energy bills;

  • Are bothered by noise from the outdoors-insulation helps to muffle sound;

  • Are concerned about the effect of energy use on the environment.

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