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.
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 →
Requirement
Model Code Standard
Section
Climate zone
Every county maps to a climate zone (1–8); the zone selects your column in the insulation table
IECC 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 enforce
IECC R402.1.3 / IRC N1102.1.3
Wood-frame walls
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
Basement & crawl walls
Conditioned basements in cold zones typically need R-10 continuous or R-13 cavity insulation on the walls
IECC R402.1.3
Air sealing
A blower-door test with a maximum leakage rate (3–5 ACH50 depending on zone and edition) is mandatory alongside the R-values
IECC R402.4.1.2
Alternate compliance
UA trade-off, simulated performance, and the Energy Rating Index paths can trade insulation against windows and equipment
IECC 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.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.