Class III vapor retarders shall be permitted where any one of the conditions in Table R702.7.1 is met.
TABLE R702.7.1 CLASS III VAPOR RETARDERS
TABLE R702.7.1 CLASS III VAPOR RETARDERS
| CLIMATE ZONE | CLASS III VAPOR RETARDERS PERMITTED FOR:a |
| Marine 4 | Vented cladding over wood structural panels. |
| Vented cladding over fiberboard. | |
| Vented cladding over gypsum. | |
| Continuous insulation with R-value ≥ 2.5 over 2 × 4 wall. | |
| Continuous insulation with R-value ≥ 3.75 over 2 × 6 wall. | |
| 5 | Vented cladding over wood structural panels. |
| Vented cladding over fiberboard. | |
| Vented cladding over gypsum. | |
| Continuous insulation with R-value ≥ 5 over 2 × 4 wall. | |
| Continuous insulation with R-value ≥ 7.5 over 2 × 6 wall. | |
| 6 | Vented cladding over fiberboard. |
| Vented cladding over gypsum. | |
| Continuous insulation with R-value ≥ 7.5 over 2 × 4 wall. | |
| Continuous insulation with R-value ≥ 11.25 over 2 × 6 wall. | |
| 7 and 8 | Continuous insulation with R-value ≥ 10 over 2 × 4 wall. |
| Continuous insulation with R-value ≥ 15 over 2 × 6 wall. |
| For SI: 1 pound per cubic foot = 16 kg/m3. |
| a. Spray foam with a maximum permeance of 1.5 perms at the installed thickness, applied to the interior cavity side of wood structural panels, fiberboard, insulating sheathing or gypsum is deemed to meet the continuous insulation requirement where the spray foam R-value meets or exceeds the specified continuous insulation R-value. |