R-Value
A measure of thermal resistance — how well a material resists heat flow. Higher R-values mean better insulating performance.
In Detail
R-value is measured in ft²·°F·hr/BTU. IRC minimum R-values vary by climate zone: Zone 3 walls R-20, Zone 5 walls R-20+5ci, Zone 7 walls R-20+10ci. Assembly R-value (whole-wall) is lower than cavity insulation R-value due to thermal bridging through framing.