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vapour barrier info
Do I Need a Vapor Barrier?
Once thought to be essential throughout a home or office, vapor barriers are now strongly recommended only for certain conditions, and methods for creating a vapor barrier must be tailored to fit the climate, region, and type of wall construction. For example, the recommended vapor barrier in a home or office in a humid southern climate built with brick varies greatly from creating a vapor barrier in a cold climate in a home built with wood siding. Always refer to current local code recommendations when deciding if and how to install vapor barriers.
Avoid adding interior vapor barriers where the outer wall construction already includes a material with vapor barrier properties.
Most authorities recommend vapor barriers in certain situations:
In areas with high humidity—such as greenhouses, rooms with spas or swimming pools, and bathrooms—vapor barriers are often recommended. Consult building inspection offices for local recommendations.
In very cold climates, the use of polyethylene plastic vapor barriers between insulation and interior wallboard may be beneficial, provided all air gaps into any wall and ceiling cavities are also blocked. The exterior face of the wall or floor cavity should remain permeable in order to allow dissipation of any moisture that does enter the wall cavity.
Very hot and humid climates may benefit from an exterior vapor barrier that keeps outside humidity from penetrating into walls.
Below-grade walls and floor slabs transmit ground moisture through concrete walls or slabs. A vapor barrier against the concrete surface is generally recommended before wood framing or flooring materials are installed.
Crawl spaces benefit from a polyethylene moisture barrier placed directly over the exposed earth.
