Insulation batts and rolls come in specific widths and R-values, and the combination you need depends on your climate zone and framing spacing. Plug in your numbers and this calculator tells you exactly how many packages to buy.
Wall Dimensions
ft
ft
Insulation Specs
in
Scenario: You're insulating 56 ft of exterior wall that's 8 ft tall (448 sq ft total) with 16-inch stud spacing.
Result: With 16-inch stud spacing, batt width is 15 inches. Each batt (15 x 93 inches) covers 9.7 sq ft. You need 47 batts and 12 rolls (at ~40 sq ft per roll).
It varies by climate zone and where you're insulating. Attics: R-38 to R-60. Exterior walls: R-13 to R-21. Floors over unheated spaces: R-25 to R-30. Look up your zip code on the DOE climate zone map for exact requirements.
For R-38 batts at 15-inch width: about 189 batts. For R-38 batts at 23-inch width: about 123 batts. Alternatively, 30 rolls of unfaced R-38 at 15-inch width would cover 1,000 sq ft.
Use faced (with vapor barrier) for exterior walls and floors where moisture control matters. Use unfaced for adding layers to existing insulation in attics, or for interior walls where you're insulating for sound only.
Yes, in attics. Lay unfaced batts perpendicular to the existing insulation to reduce thermal bridging at the joists. Don't compress old insulation -- it reduces its R-value. Make sure the attic has proper ventilation.
Want to learn more before you start your project?
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