ICC Subscriptions
 
R702.7.1 Class III vapor retarders.
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


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.
Insulated sheathing with R-value ≥ 2.5 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 3.75 over 2 × 6 wall.
5 Vented cladding over wood structural panels.
Vented cladding over fiberboard.
Vented cladding over gypsum.
Insulated sheathing with R-value ≥ 5 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 7.5 over 2 × 6 wall.
6 Vented cladding over fiberboard.
Vented cladding over gypsum.
Insulated sheathing with R-value ≥ 7.5 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 11.25 over 2 × 6 wall.
7 and 8 Insulated sheathing with R-value ≥ 10 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 15 over 2 × 6 wall.

For SI: 1 pound per cubic foot = 16 kg/m3.
a. Spray foam with a minimum density of 2 lb/ft3 applied to the interior cavity side of wood structural panels, fiberboard, insulating sheathing or gypsum is deemed to meet the insulating sheathing requirement where the spray foam R-value meets or exceeds the specified insulating sheathing R-value.