Insulation R-Value & Heat Loss Calculator

Build up a wall, roof or floor assembly layer by layer and get its total R-value and U-factor, then estimate the conduction heat loss through a given area at a given indoor-outdoor temperature difference. Each layer's R-value is its per-inch R-value times its thickness; inside and outside air-film resistances are added on top. Useful for comparing insulation upgrades, sizing supplemental heat, and checking whether an assembly meets code R-values. Steady-state conduction only — real building heat loss also includes air infiltration, thermal bridging at studs, and solar/internal gains. Pure arithmetic, in your browser.