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A field investigation of wood-framed wall assemblies was conducted to monitor the moisture performance of various exterior wall constructions with intentional air leakage and seasonal moisture injections between the cladding and sheathing over a 20-month period from November 2013 to June 2015. The research focused on four specific studies: moisture performance of Extended Plate and Beam (EP&B) walls, walls with air leakage versus air sealing, 2x4 walls with various types of exterior insulation, and baseline walls insulated with kraft-faced batts and unfaced batts. This report covers the field monitoring results and compares the performance of the 10 wall pairs.
This study is designed to document construction practices and obtain performance data for new houses framed in the fall of 2009 in the same geographical areas and by the same builders that experienced buckling of OSB wall sheathing in the winter of 2008-2009.
Recent changes in the minimum energy code (2012/2015 IECC) significantly increased wall insulation levels and reduced wall air leakage targets for light-frame wood walls, relative to the 2006 and 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 residential buildings.
High-performance homes offer improved comfort, lower utility bills, and assured durability. The next generation of building enclosures is a key step toward achieving high-performance goals through decreasing energy load demand and enabling advanced space-conditioning systems. Yet the adoption of high-R enclosures and particularly high-R walls has been a slow-growing trend because mainstream builders are hesitant to make the transition. In a survey of builders on this topic, one of the challenges identified is an industry-wide concern about the long-term moisture performance of energy-efficient walls. This study takes a step toward addressing this concern through direct monitoring of the moisture performance of high-R walls in occupied homes in several climate zones. In addition, the robustness of the design and modeling tools for selecting high-R wall solutions is evaluated using the monitored data from the field. The information and knowledge gained through this research will provide an objective basis for decision-making so that builders can implement advanced designs with confidence.
The addendum is intended to complement the Moisture Performance of High-R Wall Systems report. This Addendum summarizes the results of extended monitoring that continued through April of 2018. The goal of the extended monitoring is to capture the performance through an additional winter season, after the construction moisture had an opportunity to dissipate, so that the observed results are representative of expected long-term trends in wall performance. Monitoring through an additional year also provides data for a different set of climatic and indoor conditions.
A 22-month field investigation of nine different north- and south-oriented wood-framed wall assemblies was conducted to determine the moisture performance of various wall construction types, most of which incorporated absorptive cladding. The study was conducted on the campus of the National Association of Home Builders (NAHB) Home Innovation, in Upper Marlboro, MD, 20 miles east of Washington, DC, in a mixed humid climate.
Vapor retarders are used primarily in cold climates to prevent moisture present in warm indoor air (as water vapor) from entering wall assemblies and condensing on cold exterior sheathing. Where installed properly, vapor retarders such as Kraft paper or polyethylene sheeting have been used successfully for decades in conventional wall assemblies. However, changing wall construction practices which include new energy efficient materials and solutions that dramatically alter the moisture behavior of walls prompted questions from many builders on the appropriate selection of vapor retarders.
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. This report provides some of that guidance and the research findings behind it.