Commercial Building Inspector B2Building EnclosureHard
A commercial building inspector is examining the installation of exterior wall insulation in a Climate Zone 6 commercial building. The insulation is installed in 2x6 wood stud cavities and consists of fiberglass batts. According to IECC Table C402.1.3, what is the minimum prescriptive R-value required for the cavity insulation in this opaque wall assembly?
- AR-19
- BR-13
- CR-20
- DR-21
Show answer & explanationAnswer & explanation
Correct answer: C. R-20
According to IECC Table C402.1.3 for Climate Zone 6, the minimum prescriptive R-value for wood-framed walls with cavity insulation is R-20. This assumes the wall also has continuous insulation (CI) as part of the overall R-value requirement, but for cavity insulation specifically in 2x6 framing, R-20 is the minimum.
Why the other options are wrong
- A. R-19 is a common batt size for 2x6, but in Climate Zone 6, R-20 is the prescriptive minimum for cavity insulation.
- B. R-13 is typically for 2x4 framing in less severe climate zones.
- D. R-21 is a higher R-value batt sometimes used in 2x6, but R-20 is the minimum.
Cavity Insulation R-Value (IECC Climate Zone 6)
The minimum thermal resistance (R-value) required for insulation installed within the stud cavities of wood-framed walls in Climate Zone 6.
- Climate Zone 6 is a cold climate zone.
- IECC Table C402.1.3 specifies prescriptive R-values.
- For 2x6 wood-framed walls, minimum R-20 cavity insulation.
Memory trick: Six zones, Twenty R-value for 2x6 cavity.