1404.3 Vapor Retarders
Class I and II vapor retarders shall not be provided on the interior side of frame walls in Zones 1 and 2. Class I vapor retarders shall not be provided on the interior side of frame walls in Zones 3 and 4 other than Marine 4. Class I or II vapor retarders shall be provided on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4. The appropriate zone shall be selected in accordance with Chapter 3 [CE] of the International Energy Conservation Code-Commercial Provisions.
Exceptions:
- Basement walls.
- Below-grade portion of any wall.
- Construction where moisture or its freezing will not damage the materials.
- Conditions where Class III vapor retarders are required in Section 1404.3.2.
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 |
| Marine 4 | Vented cladding over wood structural panels Vented cladding over fiberboard Vented cladding over gypsum Continuous insulation with R-value ≥ R2.5 over 2 × 4 wall Continuous insulation with R-value ≥ R3.75 over 2 × 6 wall |
| 5 | Vented cladding over wood structural panels Vented cladding over fiberboard Vented cladding over gypsum Continuous insulation with R-value ≥ R5 over 2 × 4 wall Continuous insulation with R-value ≥ R7.5 over 2 × 6 wall |
| 6 | Vented cladding over fiberboard Vented cladding over gypsum Continuous insulation with R-value ≥ R7.5 over 2 × 4 wall Continuous insulation with R-value ≥ R11.25 over 2 × 6 wall |
| 7 and 8 | Continuous insulation with R-value ≥ R10 over 2 × 4 wall Continuous insulation with R-value ≥ R15 over 2 × 6 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.
The vapor retarder class shall be based on the manufacturer's certified testing or a tested assembly.
The following shall be deemed to meet the class specified:
| Class I: | Sheet polyethylene, nonperforated aluminum foil with a perm rating of less than or equal to 0.1. |
| Class II: | Kraft-faced fiberglass batts or paint with a perm rating greater than 0.1 and less than or equal to 1.0. |
| Class III: | Latex or enamel paint with a perm rating of greater than 1.0 and less than or equal to 10.0. |
For the purposes of this section, vented cladding shall include the following minimum clear airspaces: