Recommended Attic Insulation Depth

Climates

• Houses in cold climates require more insulation than those in warm climates. Insulation is important in both climates as both heating and air conditioning costs are reduced with adequate insulation. Locations with climates similar to those north of the Mason-Dixon Line need about R-49 insulation. More southerly locations require about R-38 insulation values.

Existing Insulation

• Most houses, even old ones, have some insulation in the attic. The existing R-value in your attic can be subtracted from the total R-value required. For instance, a house in a warm climate that already has R-20 in the attic needs another R-18 to bring it up to par.

R-Value to Inches Ratio

• Each type of insulation material has a specific R-value per inch of material. Blown-in cellulose is R-3.5 per inch, fiberglass batting is R-3.2 per inch and blown-in fiberglass is R-2.5 per inch. As an example, if you are starting with no insulation in your Georgia attic, you'll need 10.8 inches of blown-in cellulose to achieve the recommended R-38. Likewise, if you already have R-24 in your Minnesota attic, you'll need to add 7.8 inches of fiberglass batting to reach R-49.

Tips/Safety

• Do this job in spring and fall, when the attic is a comfortable temperature. Wear clothing that covers your whole body and follow your product's safety precautions regarding face or dust masks and eye protection. Protect your head from overhead nails with a hard hat. Be careful wear you step. If the attic has a permanent subfloor, it's safe to walk and crawl upon. Otherwise, take about four boards up with you that you can spread across the joists to give your knees and shoes a secure place to rest without falling through the ceiling below.