Do you need a Vapor Barrier or Vapor Retarder?

In this video, we’re going to discuss how vapor moves through these two, their different perm ratings, where they are used and how climate zones affect their installation.

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Chapters
0:00 Introduction
0:26 Diffusion
0:59 Perm ratings
3:05 Where to use
4:18 Sponsorship
4:58 Climate zones
5:34 Conclusion

Diffusion is the movement of water vapor molecules through porous materials, typically from the side with high vapor pressure or warm air to the side with low vapor pressure or cold air. In cold climates, water vapor moves from the warmer interior to the cooler exterior. In hot climates, water vapor moves from the warm exterior to the cooler interior. Vapor barriers like this plastic sheet keep rain out and stop vapor diffusion. Vapor retarders stop water but slow down vapor diffusion.

Perm ratings measure the ability of a material to let water vapor pass through. The lower the number, the less likely it is to allow water vapor through. Class 1 materials are vapor impermeable or vapor barriers and have a perm rating of 0.1 or less. Some examples are glass, aluminum foil, cork, rubber or vinyl flooring, 6mil polyethylene, sheet metal and foil faced polyiso

Class 2 materials are semi-impermeable and have a perm rating of 0.1 to 1. Some examples are vapor retarder latex paint, oil based paint, asphalt coated kraft paper, foil faced fiberglass insulation, 2” closed cell spray foam, 1” XPS and kraft paper on insulation

Class 3 materials are semi-permeable and have a perm rating of 1 to 10. Some examples are 3” EPS, OSB or Oriented Strand Board, tar paper, 2” MDF or Medium Density Fiberboard, fluid applied vapor retarders, latex paint and plywood sheathing

Class 4 materials are vapor permeable and have a perm rating of over 10. Some examples are wood siding, zip coating, plaster on metal lath, rockwool, cellulose insulation, brick and Tyvek

Now let’s discuss where these are used. In the past, builders used plastic sheets behind drywall. Unfortunately, these vapor barriers caused mold to build up behind the wall, because vapor couldn’t escape. Products like thick XPS, polyiso and closed cell spray foam can also act as vapor barriers.
There are certain instances where you’d want a vapor barrier in your wall. Interior pools or museums, which have high humidity levels need a vapor barrier to stop an excessive amount of vapor entering the walls.

Even though vapor barriers aren’t used in walls anymore, they are still used underneath slab-on-grade foundations, under the concrete slab of basements, and under crawl spaces. Plastic sheets protect concrete from moisture in the ground. They are also resistant to corrosion and punctures. Two popular brands are ISI Building Products and Stego.

Vapor retarders that also act as air and water resistive barriers are widely used on walls nowadays. They can either be peel and stick membranes or attached with staples to a substrate. Some examples are Siga, Delta and Zip system sheathing.

Finally, the code requirements for vapor barriers and vapor retarders. These vary depending on the climate zone you live in. In warm climate zones 1,2,3 and 4, the International Residential Code does not require or prohibit the use of vapor retarders. You can use one exterior side to slow the movement of vapor. In cold climate zones 5,6,7 and Marine 4, code requires either a Class 1 or 2 vapor retarder on the interior side to limit the movement of vapor through the wall assembly. Any water vapor on the outside can still dry out provided your cladding is properly vented.

So, the consensus is to avoid plastic sheets and vapor barriers. Water vapor is going to get in either through air or through your foundation. You can’t avoid it, so let the walls dry out by using vapor retarders. Another trend in the building science community is to prioritize air barriers and stop air infiltration. A study has shown that in most cold climates, over an entire heating season, a 4’x8’ sheet of drywall will let just ⅓ quart of water through by diffusion. But if that same sheet of drywall has a tiny 1 inch by 1 inch hole, moisture-laden air can sneak through and bring in 30 quarts of water.
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#vapor #retarder #zip #barrier #moisturecontrol #vaporcontrol

Видео Do you need a Vapor Barrier or Vapor Retarder? канала Belinda Carr