Understanding R Value

The classification used for insulation is the R value. The R value indicates how much heat can pass through the insulation. Typical insulation R values range from 11 to 60, and the larger the number is, the less heat can pass through.

Consider the Climate

The U.S. Department of Energy recommends R values of 30 to 60 for attic insulation, depending on your area's climate. Typically, homes located in the southern U.S. need less insulation than homes in the north. The U.S. Department of Energy provides an insulation calculator based on your zip code on their website.

Batts or Blown-in

Insulation batts, which are blanket-like pieces, and blown-in insulation are the most common types of attic installation. Batts have a set R value. Blown-in insulation requires a machine for installation and the thickness of application determines R value.

Calculating Amount

Measure the length and width of your attic in feet and multiply to calculate square footage. Insulation bags are labeled by the number of square feet they cover, so divide your total square feet by the square feet per bag to get the total number of bags you need.

Other Factors

R value is cumulative, so existing insulation in your attic counts towards the total R value. Measure existing insulation to find its R value, which is approximately three times the thickness in inches. Never compress insulation batts when installing them, as this will reduce their R value.

Source:

U.S. Department of Energy

Resource:

Zip Code Insulation Calculator