Insulation R-Value by Climate Zone (IECC 2021)
Minimum R-values for new construction per 2021 IRC N1102.1.2. Values shown are the prescriptive path — the simplest option, not the only one. More insulation always outperforms the minimum.
ci = continuous insulation (exterior foam board or similar). If you're unsure of your zone, look it up at energycodes.gov. Most of the continental US falls in Zones 3–6.
| Zone | Ceiling (attic) | Wall cavity | Floor | Basement wall |
|---|---|---|---|---|
| Zone 1 | R-30 | R-13 | R-13 | R-0 |
| Zone 2 | R-38 | R-13 | R-13 | R-0 |
| Zone 3 | R-38 | R-20 or R-13+5ci | R-19 | R-5ci or R-13 |
| Zone 4 | R-49 | R-20 or R-13+5ci | R-19 | R-10ci or R-13+5ci |
| Zone 5 | R-49 | R-20+5ci or R-13+10ci | R-30 | R-15ci or R-19+5ci |
| Zone 6 | R-49 | R-20+5ci or R-13+10ci | R-30 | R-15ci or R-19+5ci |
| Zone 7 | R-49 | R-21+12ci or R-13+15ci | R-38 | R-15ci+R-4 or R-19+8ci |
| Zone 8 | R-49 | R-21+16ci | R-38 | R-15ci+R-4 |
Important notes
- • Values are minimums for the prescriptive path — performance and U-factor paths may differ.
- • Local code amendments can require higher R-values. Always verify with your local building department.
- • Existing homes doing energy upgrades may qualify for exceptions — check your local adopted code edition.
- • Vapor retarder class requirements depend on climate zone and assembly type.