GlenCalc

Insulation calculator

Insulation bags state how much area they cover at each R-value. Enter the area and that coverage figure to get the bags to buy.

From the chart on the bag: blown-in bags cover less area at higher R-values.

For batts between studs or joists, about 10% of a wall is framing. For blown-in over joists, use 0.

Your answer

Bags34 bags
Area to insulate1,200 sq ft

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How we worked it out

Updated as you change the numbers.

  1. Area = length × width = 40 ft × 30 ft = 1,200 sq ft.
  2. Bags = area ÷ 36 sq ft per bag at R-49, rounded up.
An area to cover, with its length, width and depth markedlengthwidthdepth

Method and assumptions

The coverage chart on each bag already accounts for the depth needed for each R-value, so bags = area ÷ coverage. The US Department of Energy recommends roughly R-30 to R-60 for attics depending on climate zone; walls are limited by stud depth (R-13 to R-15 for 2×4, R-19 to R-21 for 2×6).

Questions

How many bags of blown-in insulation for a 1,200 sq ft attic?

At 36 sq ft per bag for R-49, 34 bags.

Sources

Method and figures checked on . Every worked answer on this page is covered by an automated test. Found a mistake? Tell us.

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