Envelope R-values by climate zone

North Carolina climate zones#

Most of North Carolina is in Climate Zone 3A. The northwest mountain counties and a few higher-elevation areas fall in Climate Zone 4A. Confirm the climate zone for the specific jurisdiction before designing the envelope.

The climate zone determines the prescriptive R-value path and the compliance margins for UA trade-off and RES-Check performance paths.

Prescriptive R-values (Climate Zone 3)Table N1102.1.2#

For a new home in Climate Zone 3 taking the prescriptive path, the minimums are typically:

• Ceiling: R-38
• Wood-frame wall: R-20 cavity, or R-13 cavity plus R-5 continuous exterior insulation
• Floor over unconditioned space: R-19
• Basement wall: R-5 continuous or R-13 cavity
• Slab perimeter: R-0 (not required in Zone 3)
• Crawl space wall: R-5 continuous or R-13 cavity

Three compliance paths#

You can prove energy code compliance using any one of three paths:

• Prescriptive: meet or exceed every R-value in the adopted table
• UA trade-off: use the REScheck tool or equivalent to show the assembly UA is equal to or less than the prescriptive UA
• Performance: use energy modeling software to show the design home uses no more energy than a reference home at the same square footage

Air sealingN1102.4#

Blower-door testing is required for new construction. The target is typically 5 ACH50 or less in Climate Zone 3, confirmed by a whole-house pressure test performed by a certified tester.

Common air-leak failure points: unsealed penetrations for plumbing and electrical, rim joist, attic access, and fireplace flue surround.

Common inspection flags#

Frequent energy-code failures:

• Wall assembly specified as R-13 cavity alone in Zone 3 without the R-5 continuous exterior
• Ceiling R-38 reduced at eaves where insulation is compressed against the roof deck
• Crawl space wall insulation missing where the crawl is conditioned
• Blower-door test result over 5 ACH50
• Rim joist not air-sealed before insulation