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Do you need a vapor barrier with spray foam insulation?

In houses with spray foam insulation, however, vapor barriers are not necessary. Quality closed cell foam insulation acts as a vapor barrier and does not absorb moisture; at the same time, the insulation prevents leakage by closing air gaps.

nesbuildingsolutions.com - Do I need a vapor barrier with spray foam insulation?
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Do I need a vapor barrier with spray foam insulation?

Spray insulation foam itself acts as a vapor barrier.

Vapor barriers were traditionally applied as an attempt to curb utility costs. The thought was that preventing water movement from outside the house to inside would reduce energy costs. Ultimately vapor barriers often caused more harm than good. Moisture can come inside a house through air leaks or gaps at the edge of baseboards. If these gaps were fully sealed, we would have no need to worry about vapor. However, existing gaps and the vapor barriers themselves can provoke these issues. Vapor barriers can be damaging to walls in the case that water gets trapped inside the house. When the temperature difference is great enough, a house can “sweat.” If the vapor barrier prevents this moisture from escaping, it risks damaging the wood and integrity of the walls. With traditional insulation, the moisture can quickly become a mold problem. For these reasons, a house needs to breathe while preventing the walls from retaining moisture. A house that has movement of air can more easily control the movement of water. There are a few environmental conditions where they advise installing a vapor barrier. In very hot climates or very cold climates, the vapor barrier serves to prevent moisture from being trapped in the house. Hot, humid climates should install vapor barriers and may add exterior vapor barriers for extra protection. Cold climates should use polyethylene plastic vapor barriers between the wall and insulation. Vapor barriers are often installed in basements and crawl spaces to prevent ground moisture from leaking in.

In houses with spray foam insulation, however, vapor barriers are not necessary.

Quality closed cell foam insulation acts as a vapor barrier and does not absorb moisture; at the same time, the insulation prevents leakage by closing air gaps. With proper installation of foam insulation, the house should be well sealed and allow the house to breathe.

Go back to home for: Minnesota spray foam insulation

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What material can be used as a vapor barrier?

Materials such as rigid foam insulation, reinforced plastics, aluminum, and stainless steel are relatively resistant to water vapor diffusion. These types of vapor retarders are usually mechanically fastened and sealed at the joints.

energy.gov - Vapor Barriers or Vapor Retarders - Department of Energy

In most U.S. climates, vapor barriers, or -- more accurately -- vapor diffusion retarders (vapor retarders), should be part of a moisture control strategy for a home. A vapor retarder is a material that reduces the rate at which water vapor can move through a material. The older term "vapor barrier" is still used even though "vapor retarder" is more accurate. The ability of a material to retard the diffusion of water vapor is measured in units known as "perms" or permeability. The International Residential Code describes three classes of water vapor retarders:

Class I vapor retarders (0.1 perms or less):

Glass

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

Plywood

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

Brick

15-pound asphalt coated paper

House wrap

Vapor retarders can help control moisture in:

Basements

Ceilings

Crawlspaces

Floors

Slab-on-grade foundations

Walls

Effective moisture control in these areas and throughout a home must also include air-sealing gaps in the structure, not just the use of a vapor retarder. How, where, and whether you need a vapor retarder depends on the climate and the construction of your home.

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