This building material R-value reference lists thermal resistance values for all common insulation products and building materials. R-values are shown per inch so you can calculate the total R for any thickness. Also includes DOE-recommended R-values by climate zone.
R-Value Calculator
Calculate total R-value for a given material and thickness.
How to Use the R-Value Reference
R-values are additive — add all the R-values in your wall or ceiling assembly to get the total thermal resistance. A typical 2×4 wall assembly: R-1.25 (½" drywall) + R-13 (fiberglass batt) + R-0.44 (½" plywood) + R-1 (vinyl siding) = approximately R-15.7 total.
Calculating Total R from Per-Inch Values
Multiply the R-per-inch value by the thickness in inches. A 2×4 stud cavity is 3.5 inches deep. Fiberglass batt at R-3.1/inch × 3.5 inches = R-10.85. Cavity fill (blown-in) at R-3.4/inch × 3.5 inches = R-11.9. Use the calculator above for any thickness and material.
Thermal Bridging Reduction
Wood framing studs have a much lower R-value than insulation (R-1.25/inch vs R-3.1-6.5/inch for insulation). In a standard 16" OC framed wall, about 15-20% of the wall area is solid wood framing, which reduces the whole-wall R-value significantly below the cavity R-value. To reduce thermal bridging, add continuous exterior rigid foam insulation — even 1" of polyiso (R-6.5) across the entire wall reduces thermal bridging substantially.
Climate Zone Overview
The US has 8 climate zones. Zone 1-2 covers Florida and Hawaii (hot/humid). Zone 3-4 covers the Southeast and mid-Atlantic. Zone 5 covers the northern US. Zone 6-7 covers the upper Midwest, New England, and mountain states. Zone 8 is Alaska. The DOE recommendations table shows target R-values for each zone and building section.
FAQ
Is this R-value reference free?
Yes, completely free with no signup required.
Is my data safe when using this tool?
Yes. This reference runs entirely in your browser. No data is sent to any server.
What does R-value mean in insulation?
R-value measures thermal resistance — how well a material resists heat flow. Higher R-values mean better insulation. R-value is additive: two R-13 batts combined give R-26. It is measured per inch for loose-fill and foam materials, or as a total for batts.
What R-value do I need for my attic?
The US Department of Energy recommends R-38 to R-60 for attics depending on climate zone. Climate Zone 1-2 (hot/humid, like Florida/Texas) needs R-30 to R-60. Climate Zone 5-7 (cold, like Minnesota/Maine) needs R-49 to R-60. New construction should target R-60 for maximum energy savings.
Is spray foam better than fiberglass insulation?
Closed-cell spray foam has the highest R-value per inch (R-6.5 vs R-3.1 for fiberglass batt). It also acts as an air and vapor barrier. However, it costs 3-5x more and requires professional installation. For tight spaces or areas needing air sealing, spray foam is worth the premium. For standard wall cavities, fiberglass or mineral wool batts are cost-effective.
What R-value should exterior walls have?
The International Energy Conservation Code (IECC) requires R-13 to R-21 for wall insulation depending on climate zone. Standard 2×4 walls with fiberglass batts achieve R-13 to R-15. 2×6 walls allow R-19 to R-21 batts. Adding rigid foam exterior insulation can bring walls to R-25 or higher.