How to Measure an Attic for Cellulose

Measure the width and depth of your attic using measuring tape. Measure from the outermost part of the attic and not from the rafters or floor joists. If the attic has several sections, then treat each area separately, squaring off each section and measuring its width and depth.

Multiply the width of the attic, or the width of an attic section, by its depth to obtain the area's square footage. Multiply the square footage by 16 inches. The result is the maximum amount of cellulose insulation the attic or section should need. Sixteen inches is the recommended depth for insulating an attic to an R-60 value with cellulose fiber.

Subtract the amount of insulation already in the attic from the amount of insulation needed. If, for instance, the attic has 6-inch thick fiberglass batting, subtract its 6 inches from 16 inches to get 10 inches of insulation depth. Use the result in conjunction with the square footage to arrive at the amount of cellulose insulation to obtain for the attic.