Construction & Home
R-Value
Updated 2026-01-25
Definition
A measure of thermal resistance for insulation materials. Higher R-values mean better insulating performance. The Department of Energy recommends attic insulation of R-30 to R-60 for most U.S. climate zones, wall insulation of R-13 to R-21, and floor insulation of R-25 to R-30. Fiberglass batts deliver roughly R-3.1 to R-3.4 per inch; closed-cell spray foam hits R-6 to R-7 per inch but costs 3-4 times as much. R-values are additive: two layers of R-15 batts equal R-30.
Primary source: DOE insulation guide
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