calcs.homes
calcs.homes
Add up your wall or ceiling assembly's layers — insulation, sheathing, drywall, and air films — to see the total R-value against your target. Uses the US/Imperial R-value scale printed on North American insulation products.
Estimate only — includes a standard air film allowance (R-0.85) for interior and exterior surfaces.
Total R-value is simply the sum of every layer's individual R-value: insulation (material R-value per inch × thickness), sheathing, drywall, and a small standard allowance for the air films that cling to interior and exterior surfaces. This calculator doesn't account for thermal bridging through studs, which lowers the real-world "effective" R-value below this material-only total.
It depends on your climate zone — many US codes call for R-13 to R-21 in 2x4 or 2x6 walls. Check your local energy code for the exact requirement.
Wood studs conduct heat faster than insulation (thermal bridging), so a wall's "effective" R-value is typically 10-20% lower than the simple sum of its layers — continuous exterior rigid foam is a common way to reduce this effect.