Home Insulation R-Value Calculator
Calculate the total thermal resistance (R-value) of your home insulation to determine energy efficiency. Add multiple insulation layers for a complete wall or ceiling assembly.
Insulation Layers
Add one or more insulation layers. R-values are additive for layers in series.
Surface Air Films (Auto-included)
Formulas Used
Total R-Value (series layers):
Rtotal = Rint.film + Σ(Rlayer) + Rext.film
Where for each layer: Rlayer = rmaterial × thickness (inches)
rmaterial = R-value per inch of the selected insulation material (h·ft²·°F/BTU per inch)
U-Factor: U = 1 / Rtotal
Heat Loss (BTU/hr): Q = U × A × ΔT, where A = area (ft²), ΔT = indoor–outdoor temperature difference (°F)
Assumptions & References
- R-values per inch are based on ASHRAE Handbook of Fundamentals and DOE/Oak Ridge National Laboratory data.
- Air film resistances follow ASHRAE 90.1 standard surface conditions.
- Recommended R-values by climate zone are from DOE Energy Saver / IECC 2021 guidelines.
- Calculations assume 1-D steady-state heat transfer (no thermal bridging through studs or framing).
- Actual performance may be lower due to thermal bridging, air leakage, and installation quality.
- Framing typically reduces effective R-value by 10–25% depending on stud spacing.
- R-values are in imperial units: h·ft²·°F/BTU.