The July 2017 Technical Bulletin published by the Duke Energy Progress RNC Program, “Grading Insulation Installation,” contained an omission regarding Grade I insulation in Climate Zone 3. Insulation in these homes may still achieve a Grade I rating without interior sheathing/enclosure provided insulation is adequately supported (e.g. with webbing, staples, straps, etc.) and meets all other requirements for Grade I insulation.
Please note that while allowable, omitting interior sheathing in homes in Climate Zone 3 is not recommended by the Duke Energy Progress RNC Program due to negative air sealing impacts. Failing to install interior sheathing will hurt a home’s chances of meeting the 4.0 ACH50 requirement of the HERO Code.