What Are the Requirements for Attic Insulation?

Thermal Envelope

• By creating a thermal envelope for your home that includes the roof, attic, walls and basement, you can achieve the most efficient system for cutting costs of heating and cooling your home. The Energy Star Thermal By-pass Checklist is a guideline that delineates the energy efficiency of the type of insulation used. Certain criteria must be met to comply with this checklist. Insulation in the attic is a crucial part of the thermal envelope.

Types of Insulation

• The requirements for insulating an attic are dependent on the type of insulation installed. A number of different types are used: loose-fill, rigid foam, sprayed foam or foamed-in-place and blankets, which are available in rolls or batts and are generally made of fiberglass, natural fibers and rock wool. Loose-fill insulation consists of these elements in addition to cellulose fibers and polyurethane and polyicynene. Foam insulation is available in polyisocyanurate, polyurethane and extruded or expanded polystyrene foam (XPS or EPS).

R-Values

• The thermal resistance, or R-value, of insulation measures its resistance to heat gain or loss. The higher the number, the more efficient the insulation. Energy codes regulating attic insulation vary from climate to climate and are based on the R-value. For example, an R-value of at least 38 is the requirement for both zones in the state of Washington, which is set by the Washington State Energy Code (WSEC). Check with the codes for your state to determine the R-value requirements. An R-38 constitutes a depth of 10 to 12 inches of insulation containing cellulose and about 14 to 17 inches for fiberglass insulation.

Vapor Retarder

• Condensation forms when moist air comes in contact with cooler air or a cold surface. This action occurs in your home in the same manner. A vapor retarder controls the movement of air and vapor through the insulation, restricting the moisture content. Different types of insulation require a certain vapor retarder, which may not be needed with polyurethane and polyicynene sprayed-in insulation. Blanket insulation generally incorporates the vapor retarder into the makeup of the insulation, and rigid board insulation is its own retardant when properly placed. Consult local building codes in regards to the vapor retarder requirements.