Characterization of the Moisture Performance of Energy Efficient and Conventional Light Frame and Wood Wall Systems

The recent changes in the minimum energy codes (2012 IECC) resulted in increased wall insulation levels and reduced wall air leakage for all light-frame wood systems (relative to 2009 IECC). The long-term moisture performance of these new wall systems is not well understood with regard to vapor drive, condensation risk, and drying capability. With moisture performance increasingly becoming a design consideration in the selection of wall systems, home builders and designers need practical guidance for construction of walls that ensure durability of wood buildings. This type of design guidance is particularly needed as various industry groups are advocating specific wall design solutions based on incomplete information.

The project this report is based upon involves monitoring of the moisture performance of wall assemblies with specific design characteristics using the Home Innovation Research Labs outdoor Test Hut facility located in Climate Zone 4. Six configurations of energy-efficient walls are studied: four with exterior rigid foam with the study variables including different levels of cavity insulation and types of water resistive barrier; and two with 2x6 framing with different interior vapor retarders (Kraft-facing vs. gypsum with interior paint only). In addition, six conventional 2x4 wood-frame wall systems with varying cladding materials including stucco, manufactured stone, vinyl siding, brick, and fiber cement siding are under continued monitoring as follow-up research to the previous studies. Specifically, the impact of the interior vapor retarder on the performance of these conventional systems in Climate Zone 4 is studied. Cedar siding has been added in this monitoring phase to expand the library of cladding systems under testing at Home Innovation.

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