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Insulation Basics

Insulation is one of the most effective ways to save energy. Heating and cooling costs comprise more than 50% of the energy consumed in a single family home. Adding the recommended levels of insulation will save energy, reduce utility costs and improve comfort. Proper installation is critical; gaps and compressed areas will dramatically reduce effectiveness.

Insulation provides additional benefits including noise reduction, fire resistance and safety. Factors that affect the performance of insulation, and should be considered when choosing the appropriate type for the job, are insulating capacity, fire resistance, moisture control, convective heat loss, settling and loss of insulating capacity.

Before You Insulate

  • Conduct thorough air sealing. Adding insulation may make some air leaks difficult to access. The insulation itself typically will not stop these leaks. Air flowing through the insulation will waste energy. Moist air can damage the insulation and reduce its effectiveness.
  • Control moisture. Rain can penetrate through improper flashing and leaks around doors, windows, chimneys and poorly-installed siding. Fix these problems and install a vapor retarder. Remove any existing insulation that has gotten wet.
  • Check your building code to determine if you need to add ventilation (in attics and crawlspaces). Ensure that insulation will not block existing vents.
  • Inspect the area for any exposed wiring. Be sure it is in good condition and will not present a fire hazard.
  • Recessed light fixtures can be a major source of heat loss, but you need to be careful how close you place insulation next to a fixture unless it is marked "I.C."-designed for direct insulation contact. Check your local building codes for recommendations.

Where to Insulate

Energy professional installs cellulose insulation into walls. Walls, ceilings, attics, floors and ducts should be well-insulated. Insulation is rated according to its R-Value, or its ability to resist heat flow, with a high R-Value being a greater resistance.

Ceilings: Attics are easy to access in single family homes and low multifamily buildings with pitched roofs. Multi-family buildings with flat roofs should be insulated when roof replacement or repair work is needed.

Exterior Walls: Wall insulation is often difficult to upgrade unless the interior walls (drywall or other wallboard) or the exterior siding are being replaced in the rehabilitation project. Existing uninsulated frame walls can often have their cavities filled with blown-in cellulose insulation in a cost-effective manner. If the outside siding is being replaced, it is often cost effective to apply rigid foam insulation on the outside of the framing before the siding is installed.

Floors: Floors are usually easy to access. If the basement or space underneath the floor is not conditioned (like a garage), uninsulated floors can be a significant source of heat loss from the living space.

Basements: If the basement space is conditioned and the climate is cold, uninsulated basement walls will be a significant source of heat loss. Basement insulation systems must be carefully considered because of the inherent moisture problems and the resulting mold problems that may be exacerbated by inappropriately insulating a basement. Furring out and insulating the inside of the wall is often possible and cost-effective. Generally, if below-grade walls "sweat" or if moisture is a problem at these walls, only insulate the above-grade portion of the walls.

Crawl Spaces: The perimeter walls of enclosed crawl spaces should be insulated in cold climates. For ventilated crawl spaces, the floor above should be insulated.

**Caution: Many types of insulation used before the 1980s contain asbestos, which, if disturbed, is a dangerous material.

 Types of Insulation
 Duct Sealing and Insulation
 Air Sealing
 Vapor Retarders
 HVAC Main
 Incentives Available for Insulation
 DOE's Insulating Foundations
 DOE's Perimeter Slab Insulation Information
 DOE's How to Install Housewrap Fact Sheet (pdf)
 Basement Insulation Systems

Content updated May 28, 2009

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