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Vapor Retardant Addresses Moisture Concerns

A newly introduced vapor retardant that breathes and allows excess moisture to escape from wall cavities will help minimize builders’ concerns over excess moisture trapped in walls and roofs leading to mold and liability problems, according to CertainTeed Corporation.

Headquartered in Valley Forge, PA, CertainTeed is a member of the National Council of the Housing Industry — the Supplier 100 of NAHB.

MemBrain™ is the first product of its kind to be introduced in the U.S., its manufacturer says. The sheeting has been designed for use with un-faced, vapor permeable mass insulation (fiber glass and mineral wool) in wall and ceiling cavities.

The product is ideal for areas with seasonal changes in temperature and humidity, says Glenn Singer, manager of building sciences for CertainTeed’s Insulation Group.

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The new vapor retardant is a polyamide film that can become more than 20 times more permeable at high relative humidity than during times when there is low humidity, such as in the winter.

More typical polyethylene vapor retardants allow moisture to condense on cold surfaces and accumulate in the wall cavity when the seasons change.

The concept of a “smart” vapor retardant was introduced seven years ago in Europe and has become widely accepted there, CertainTeed says.

With a high resistance to water vapor diffusion in winter, says the manufacturer, the pores of MemBrain™ react to increases in the relative humidity so that water vapor can pass through. This lowered resistance supports the drying process.
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