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Home / Code Guides / Insulation R-Values

Insulation R-Value Requirements by Climate Zone

There is no single “code R-value” — there is a table, keyed to your climate zone and your state’s adopted energy code edition. The 2021 IECC raised the attic bar substantially, and states are scattered across three editions.

WOOD-FRAME WALL — INSULATION BY CLIMATE ZONE (IECC 2021)D18INTERIOREXTERIORGypsum boardCavity insulationfirst value in the tableStudsSheathingContinuous insulation (ci)second value in the tableWater-resistive barrierCladdingSection is schematic, not to scaleCLIMATE ZONEWALL R-VALUE (R402.1.3)WALL U-FACTOR MAX (R402.1.2)0–113 or 0 + 100.084213 or 0 + 100.084320 or 13 + 5ci or 0 + 150.0604 except Marine20+5 or 13 + 10ci or 0 + 150.0455 and Marine 420+5 or 13 + 10ci or 0 + 150.045620 + 5ci or 13 + 10ci or 0 + 200.0457 and 820 + 5ci or 13 + 10ci or 0 + 200.045R-values are minimums; U-factors are maximums. first value = cavity insulation, second value = continuous insulation(ci = continuous insulation).Example: 13 + 5 means R-13 cavity insulation plus R-5 continuous insulation. Layer order is illustrative; table valuesgovern.WALL INSULATION · IECC 2021 TABLE R402.1.3 (R-VALUE) · TABLE R402.1.2 (U-FACTOR)
Wall assembly R-values by climate zone — IECC 2021 Table R402.1.2. Check the edition your jurisdiction has adopted; the table is renumbered between editions.Open full diagram →
RequirementModel Code StandardSection
Climate zoneEvery county maps to a climate zone (1–8); the zone selects your column in the insulation tableIECC R301 / IRC N1101
Ceilings (2021 IECC)R-49 in zones 2–3 and R-60 in zones 4–8 — up from R-38/R-49 in the 2018 edition many states still enforceIECC R402.1.3 / IRC N1102.1.3
Wood-frame wallsRanges from R-13 cavity in the warmest zones to R-20+5ci or R-13+10ci class assemblies in cold zones; continuous insulation options trade against cavity depthIECC R402.1.3
Basement & crawl wallsConditioned basements in cold zones typically need R-10 continuous or R-13 cavity insulation on the wallsIECC R402.1.3
Air sealingA blower-door test with a maximum leakage rate (3–5 ACH50 depending on zone and edition) is mandatory alongside the R-valuesIECC R402.4.1.2
Alternate complianceUA trade-off, simulated performance, and the Energy Rating Index paths can trade insulation against windows and equipmentIECC R405, R406

Worth knowing

  • Which edition your state adopted is the whole question — a zone-5 attic is R-49 under 2018 but R-60 under 2021. Check your state’s page before quoting.
  • Raising attic insulation is cheap at the table and hard at the eave: R-60 needs ~17 in. of loose fill, which forces raised-heel trusses or baffled compression at the edges.
  • Existing homes are governed by the existing-building provisions — exposed-cavity work generally must be filled, but nobody makes you demo drywall to add R-value.
  • Insulation certificates and settled-depth markers are required at inspection for blown products — installers know this; verify it lands in the file.

Common questions

What does the code say about climate zone for Insulation R-Values?

Every county maps to a climate zone (1–8); the zone selects your column in the insulation table. (IECC R301 / IRC N1101)

What does the code say about ceilings (2021 IECC) for Insulation R-Values?

R-49 in zones 2–3 and R-60 in zones 4–8 — up from R-38/R-49 in the 2018 edition many states still enforce. (IECC R402.1.3 / IRC N1102.1.3)

What does the code say about wood-frame walls for Insulation R-Values?

Ranges from R-13 cavity in the warmest zones to R-20+5ci or R-13+10ci class assemblies in cold zones; continuous insulation options trade against cavity depth. (IECC R402.1.3)

Related sections and guides

This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org.Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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