How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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Why is housewrap installed on exterior walls under the siding?
Saturday, September 22, 2018
Siding applied over a wood stud frame house structure is water-resistant but not waterproof. It doesn’t matter whether its wood, vinyl, or fiber-cement siding, brick, or stone: water will occasionally get behind it. Also, exterior siding materials do not provide an effective seal against air leakage through the wall.
Modern housewrap—the white plastic sheeting with repetitive company logos stamped across the surface—is a barrier sheet that has the special ability to resist liquid water penetration but allow water vapor to pass through. This allows moisture to escape from the inside of the home, instead of condensing on the interior of the wall assembly and possibly causing mold growth. At the same time it prevents air movement through the wall when properly installed and taped, which adds insulation value to the wall. The most popular housewrap brand is Tyvek, manufactured by DuPont from flash-spun, high-density polyethylene fibers; but black roofing felt, also called tar paper, was the original housewrap and continues to be used by some builders.
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To learn more about exterior walls and structures, see these other blog posts:
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