1404.3.2 Class III Vapor Retarders
Class III vapor retarders shall be permitted where any one of the conditions in Table 1404.3.2 is met. Only Class III vapor retarders shall be used on the interior side of frame walls where foam plastic insulating sheathing with a perm rating of less than 1 is applied in accordance with Table 1404.3.2 on the exterior side of the frame wall.
CLASS III VAPOR RETARDERS
|ZONE||CLASS III VAPOR RETARDERS PERMITTED FOR:a|
|Vented cladding over wood structural panels |
Vented cladding over fiberboardVented cladding over gypsum Continuous insulation with R-value ≥ R3.75 over 2 × 6 wall
|5||Vented cladding over wood structural panels |
Vented cladding over fiberboardVented cladding over gypsum Continuous insulation with R-value ≥ R7.5 over 2 × 6 wall
|6||Vented cladding over fiberboard |
Vented cladding over gypsumContinuous insulation with R-value ≥ R7.5 over 2 × 4 wall
|7 and 8||Continuous insulation with R-value ≥ R10 over 2 × 4 wall|
For SI: 1 pound per cubic foot = 16 kg/m3.
- Spray foam with a maximum permanence 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 insulating sheathing R-value.