Calculate Blown Insulation Coverage in an Attic
Whether you are insulating a space for the first time or adding additional insulation, you will need to know how much insulation to buy. It would be very frustrating to begin a blow-in insulation job (setting up the machine, getting all your safety gear on, etc.) only to run out of insulation material before completing the job. Determining the amount of insulation needed is a reasonably easy and quick task that can save you some headache later.
Instructions
1. Determine the square footage of the attic space. Use a tape measure to get the length and width dimensions. Multiply these together to determine the square footage. For instance, if the attic is 12 feet by 20 feet, the square footage will equal 240 feet.
2. Measure the existing insulation depth. Use a tape measure to check the distance from top of the insulation to the attic floor. If there is no insulation installed, or if you are removing the old insulation, you can eliminate this step.
3. Determine the R value that you want to achieve. The R value is the industry number that states how well the insulation is working. R value is determined by the thickness of the insulation. Local codes vary. Check out the Department of Energy site listed in the resources for this article to determine how much insulation is recommended for your region. For the purposes of this article, we will use an example R value of 49.
4. Review the specifications of the insulation product you are going to use. AttiCat insulation, from Owens Corning lists an R value of 49 to be equal to 18 1/4 inches of insulation. Even if you have existing insulation and you don't know what kind it is, the R value to thickness ratio does not vary that much from product to product. For peace of mind, apply extra insulation. In this case we would calculate for 19 inches of thickness, subtracting the thickness of any existing insulation.
5. Further review the specifications to determine insulation coverage per bag. AttiCat states that 26 bags are required to insulate an attic space of 1000 square feet to an R 49 value. Divide 1000 by 26 to determine that one bag equals approximately 38 1/2 square feet of coverage. In our example, we would need seven bags of insulation (240 square feet divided by 38 1/2 square feet per bag equals 6.23 bags).
6. If you have subtracted existing insulation to determine that you need a lower amount of thickness to reach the recommended insulation, go back to Step 4. You can check the specs to determine what the thickness you need to add equates to in R value. For example, 10 inches of insulation would be an R value of 25. Then check the coverage specs for R 25 coverage to see that 14 bags are required for 1000 square feet of coverage. Complete the Step 5 calculations to see that you would need only four bags of insulation to bring the attic space up to the recommended R value.
Tips Warnings
Wear gloves, eye, and face protection when working with insulation. Fiberglass and cellulose fibers can be skin irritants and harmful when inhaled.
If you are unsure of the existing insulation type in your home, check with a reputable contractor to ensure that it is not an asbestos-containing material. Older homes often have asbestos materials in them.
Tags: calculate, blown, insulation, coverage, attic, existing insulation, square feet, attic space, square footage, 1000 square, 1000 square feet
