Vapor Retarders in Cold Climate Zones (5, 6, 7 and Marine 4)

The International Residential Code requires either a Class I or II vapor retarder on the interior side of frame walls in climate zones:5,6,7,8 and marine 4 - refer to the climate zone map on page 16. A vapor retarder is not required for basement walls or on any portion of the wall that is below ground,or on walls made of materials that can't be damaged by moisture or its freezing.

Class III vapor retarders can be used on the interior side of the wall in the following climate zones when any one of the conditions in the table below apply:

Climate Zone

1, 2, 3 and 4 All wall assemblies

Marine 4	*Vented cladding over OSB Vented cladding* over plywood Vented cladding* over fiberboard Vented cladding* over gypsum**
	Insulated sheathing with R-value ≥ 2.5 over 2x4 wall
	Insulated sheathing with R-value ≥ 3.75 over 2x6 wall
5	*Vented cladding over OSB Vented cladding* over plywood Vented cladding* over fiberboard Vented cladding* over gypsum**
	Insulated sheathing with R-value ≥ 5 over 2x4 wall
	Insulated sheathing with R-value ≥ 7.5 over 2x6 wall
6	*Vented cladding over fiberboard Vented cladding* over gypsum**
	Insulated sheathing with R-value ≥ 7.5 over 2x4 wall
	Insulated sheathing with R-value ≥ 11.25 over 2x6 wall
7 & 8	Insulated sheathing with R-value ≥ 10 over 2x4 wall
	Insulated sheathing with R-value ≥ 15 over 2x6 wall

* Vented Claddings include vinyl lap or horizontal aluminum siding installed over a weather resistive barrier, typically housewrap or 15 lb. building paper. Or Brick veneer with a minimum of space of 1" between the brick and the weather resistive barrier.

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Vapor Retarders in Cold Climate Zones (5, 6, 7 and Marine 4)

Climate Zone

1, 2, 3 and 4 All wall assemblies

Marine 4

**Vented cladding* over OSB**

**Vented cladding* over plywood Vented cladding* over fiberboard**

**Vented cladding* over gypsum**

Insulated sheathing with R-value ≥ 2.5 over 2x4 wall

Insulated sheathing with R-value ≥ 3.75 over 2x6 wall

5

**Vented cladding* over OSB Vented cladding* over plywood Vented cladding* over fiberboard**

**Vented cladding* over gypsum**

Insulated sheathing with R-value ≥ 5 over 2x4 wall

Insulated sheathing with R-value ≥ 7.5 over 2x6 wall

6

**Vented cladding* over fiberboard Vented cladding* over gypsum**

Insulated sheathing with R-value ≥ 7.5 over 2x4 wall

Insulated sheathing with R-value ≥ 11.25 over 2x6 wall

7 & 8

Insulated sheathing with R-value ≥ 10 over 2x4 wall

Insulated sheathing with R-value ≥ 15 over 2x6 wall

* Vented Claddings include vinyl lap or horizontal aluminum siding installed over a weather resistive barrier, typically housewrap or 15 lb. building paper. Or Brick veneer with a minimum of space of 1" between the brick and the weather resistive barrier.