Roof Vapor Barriers/ Vapor Retarders
What is a roof vapor retarder vs a roof vapor barrier?
A vapor retarder whether in the basement or on the roof is a material that reduces the rate at chich water vapor can move through a material. Theoretically a "vapor retarder" permits less permeance as it is a layer with a permeance greater than 0.1 pers but less than or equal to 1 perm. A "vapor barrier" is defined as a layer with a permeance rating of 1 perm or less. The way this is measured is by a testing facility.
At the bottom of this page will be the various classes of vapor retarders explaining each class's ability to diffuse water vapor.
The biggest differential between a crawl space vapor retarder and a roof vapor retarder is the temperatures. On the roof the heat can be intense. A heavy-duty roof vapor retarder will not only withstand the heat but be highly resistant to punctures and tears.
If building codes require a fire retardant vapor retarder, the fire retardant liners listed below will pass various fire tests. Please click on each product name below to view the data sheet to learn more about each vapor retarder.
Griffolyn® Type-65- Reinforced high density 3 ply. General-purpose that meets the strength & permeance requirements of most applications
Griffolyn® Type-85- Reinforced high density 5 ply. Offers greater strength & lower permeance for a higher level of integrity in roofing and under slab applications
Griffolyn® Type-105- Reinforced high density 7 ply. Extra strength and extra-low permeance needed to meet additional requirements
Griffolyn® VaporGuard®- 3 ply. Combines HDPE/LLDPE & aluminum to provide extremely low permeance for special applications such as radon protection, cold storage, museums & computer rooms
Griffolyn® Type-1200 FR- Reinforced 3 ply. Offers Greater strength and lower permeance. Qualifies as a Class 1 building product
Griffolyn® Type-90 FR- Reinforced fire retardant 5 ply. Delivers extra strength and extra-low permeance for applications with extreme temperature variation
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The International Residential Code describes three classes of water vapor retarders:
Class I vapor retarders (0.1 perms or less):
- Sheet metal
- Polyethylene sheet
- Rubber membrane
Class II vapor retarders (greater than 0.1 perms and less than or equal to 1.0 perms):
- Unfaced expanded or extruded polystyrene
- 30 pound asphalt coated paper
- Bitumen coated kraft paper
Class III vapor retarders (greater than 1.0 perms and less than or equal to 10 perms):
- Gypsum board
- Fiberglass insulation (unfaced)
- Cellulose insulation
- Board lumber
- Concrete block
- 15-pound asphalt coated paper
- House wrap
Vapor retarders can help control moisture in:
- Slab-on-grade foundations