Wall Insulation Calculator

Insulation R-value here comes from exactly two inputs -- Cavity / insulation depth and Insulation material -- and nothing else touches it: Total wall area, IECC Climate zone, and Energy cost per therm are all completely inert on Insulation R-value across their full declared ranges, since the achieved-R formula is simply the material's R-per-inch multiplied by depth. Deeper cavities always raise Insulation R-value, monotonically across the full 1-12 in. range. Which single input matters more for R-value -- depth or material choice -- actually depends on where you're standing: a small nudge around the calculator's defaults makes switching Insulation material look like the bigger lever (the six materials span more than 2x in R-per-inch), but sweep Cavity / insulation depth across its whole 1-12 in. range and it ends up moving Insulation R-value more than any single material swap, since depth's own range is a 12x span.

Annual wall heat loss cost responds in the opposite direction to depth: deeper insulation always lowers it, monotonically across the full range, because it directly reduces the wall's U-factor. Energy cost per therm scales it the other way -- a straightforward linear multiplier, always raising the estimated annual cost as the price of heat goes up. Code-required R-value, meanwhile, is a pure lookup: IECC Climate zone is the only input that ever changes it, since the recommended minimum comes straight from a zone table and never depends on wall area, material, depth, or energy cost.