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Attic Insulation Calculator
Before you buy, check your attic.
Insulation is available in widths to fit joists spaced 15-16" apart or 23-24" apart. Check your joist spacing before buying insulation.
If your attic has no insulation: Use kraft-faced insulation, which creates a vapor retarder. The kraft paper should go down toward the interior of the building. If you need a second layer, use unfaced insulation.
If your attic already has some insulation: Is the insulation loosefill, or batts or rolls? Use unfaced insulation whenever you're adding to batt or roll insulation already in place.
Owens Corning does not recommend installing batts or rolls over loosefill insulation. Doing so can compress existing insulation and reduce its R-Value. Instead, we recommend Owens Corning AttiCat® Blown-in Fiberglas™ insulation. The AttiCat® Blown-in Fiberglas™ insulation machine fits in an SUV for convenient DIY installation. Rent one from a Lowe's near you.
Rolls required is an estimate based on 1000 square feet of uninsulated attic space. Bags required is an estimate based on information provided. Actual needs may be slightly more or less. See your insulation retailer for additional guidance.
The calculator results are determined using the U.S. Department of Energy (DOE) recommendations on the most economic level of insulation for a residential building, considering climate, local material costs and local fuel costs. An explanation of the recommended R-values can be found on the DOE Insulation Fact Sheet.
|Zone||Attic||2x4 Walls||2x6 Walls||Floors||Crawlspaces|
|7||R49 to R60||R13 to R15||R19 to R21||R25 to R30||R25 to R30|
|6||R49 to R60||R13 to R15||R19 to R21||R25 to R30||R25 to R30|
|5||R49 to R60||R13 to R15||R19 to R21||R25 to R30||R25 to R30|
|4||R38 to R60||R13 to R15||R19 to R21||R25 to R30||R25 to R30|
|3||R30 to R60||R13 to R15||R19 to R21||R25||R19 to R25|
|2||R30 to R60||R13 to R15||R19 to R21||R13||R13 to R19|
|1||R30 to R49||R13 to R15||R19 to R21||R13||R13|
How to measure
If your attic consists of only 1 section (a rectangle), you will only need to take two measurements - the length and width for the space. Refer to the diagram below:
If your attic consists of 2 sections ("L" or "T" Shaped), you will need to take a total of four measurements - the length and width for each section of the attic. Refer to the diagram below for details: