North Carolina

SECTION 6.(b) R402 Rules Amendment. – The Council shall amend R402 Rules to include, as an optional alternative to residential ceiling insulation minimums, minimum insulation requirements for the use of air-impermeable insulation in unvented attic and unvented enclosed rafter assemblies. In developing this amendment, the Council shall include in that optional alternative that where R402 Rules require R-38 insulation in the ceiling, installing air-impermeable insulation, as follows, to the underside or directly above the roof deck shall be deemed to satisfy the R-38 requirements: (i) R-20 (equivalent U-factor 0.05) for climate zone 3; (ii) R-25 (equivalent U-factor 0.037) for climate zone 4; and (iii) R-25 (equivalent U-factor 0.037) for climate zone 5. These air-impermeable insulation alternative R-value minimums apply in residences meeting the following criteria:

• The unvented attic or unvented enclosed rafter assemblies are constructed under Section R806.5 of the North Carolina Residential Code.
• The residence contains a mechanical ventilation system that operates on a positive, balanced, or hybrid pressure strategy.
• For residences with air-impermeable insulation installed below the roof deck, exposed portions of the roof rafters are wrapped by a minimum of R-3 insulation unless directly covered by drywall or finished ceiling material. For residences with air-impermeable insulation installed above the roof deck, roof rafters do not require insulation wrapping if air-impermeable insulation installed above the roof deck is continuous.
• The residence obtains an ACH50 blower door test result of less than 3.0.
• The residence contains heating, cooling, and ventilation equipment and ductwork within thermal envelope.

Citation: HB488 (2023)