A multifamily building within the 2021 IECC commercial scope is in Climate Zone 5. Its above-grade wood-framed wall uses the Table C402.1.3 R-13 cavity plus continuous-insulation option. If the specified rigid foam provides a rated R-5 per inch, what minimum thickness provides the continuous-insulation R-value for that option?
- A1 inch
- 1.5 inches
- C2 inches
- D3 inches
Where to look it up
https://www.iccsafe.org/wp-content/uploads/errata_central/2021-International-Energy-Conservation-Code-Errata-Complete.pdf
Why B is correct
For Group R in Climate Zone 5, this wood-framed-wall option requires R-13 cavity insulation plus R-7.5 continuous insulation. At the stated product rating, 7.5 / 5 = 1.5 inches. This is a calculation for the specified option and product, not a universal foam thickness; greater thickness is not disqualified merely for exceeding the minimum. The table also provides other assembly options. Source: ICC, 2021 IECC errata, corrected Table C402.1.3, PDF p.4; https://www.iccsafe.org/wp-content/uploads/errata_central/2021-International-Energy-Conservation-Code-Errata-Complete.pdf