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Illustration of high-r wall systems.

The research from this project examined the moisture characteristics of high-R wall systems as part of a broader effort to offer solutions that increase builders’ confidence with the adoption of energy-efficient technologies. The high-R walls feature increased wall insulation levels, reduced wall air leakage, and often reduced permeance of material layers. Wall assemblies were subjected to various moisture loads, such as bulk water, built-in moisture (construction moisture), water vapor, and capillary transport through materials in contact with water or in contact with the ground. Some recommendations from this project include:

  • Because polyethylene continues to be used as an interior vapor retarder by builders in colder climates, it should be accompanied with air sealing details and drainage plane details so as to avoid or minimize the potential for water leaks and moisture accumulation.
  • Walls that rely on the combination of exterior insulation and a Class II vapor retarder show promise for increased R-value (with minimum impact to construction practices).
  • For walls without exterior sheathing and an interior vapor retarder in climate zone 4A or 4C, control of the interior relative humidity levels should be integrated into the house design strategy.

Read more about this success story on the project web page.