Attic Insulation Calculator — R-Value & Depth Guide

Understanding Attic Insulation R-Values and Depth

Attic insulation is one of the most cost-effective home improvements you can make, with the U.S. Department of Energy estimating that proper attic insulation can save 10-50% on heating and cooling costs. The key metric is R-value, which measures thermal resistance -- the higher the R-value, the better the insulation resists heat flow. The DOE recommends different R-values by climate zone, ranging from R-30 in warm southern climates up to R-60 in cold northern regions.

This calculator determines how much additional insulation you need by subtracting your existing R-value from the target for your climate zone, then dividing by the R-value per inch of your chosen material. Blown fiberglass offers about R-2.5 per inch, cellulose provides R-3.7 per inch, fiberglass batts deliver R-3.2 per inch, and open-cell spray foam achieves R-3.6 per inch. Material quantities are estimated based on your attic square footage and the required depth.

Homeowners typically insulate attics when upgrading older homes with insufficient insulation, preparing for extreme weather seasons, or reducing energy bills. Adding insulation on top of existing material is generally effective as long as the old insulation is dry and undamaged. Before insulating, seal air leaks around plumbing penetrations, electrical boxes, and recessed lights, since air sealing alone can improve energy efficiency by 15-25%.