Abstract
Long-term moisture performance is a critical consideration for design and construction of building envelopes in energy-efficient buildings, yet field measurements of moisture characteristics for highly insulated wood-frame walls in mixed-humid climates are lacking. Temperature, relative humidity, and moisture content of wood framing and oriented strand board (OSB) structural panel sheathing were measured over a period from mid-November 2011 through March 2013 in both north- and south-facing orientations in test structures near Washington, DC, USA. Wall configurations varied in exterior cladding, water-resistive barrier, level of cavity insulation, presence of exterior continuous insulation, and interior vapor retarder. The combination of high interior humidity and high vapor permeance of painted gypsum board led to significant moisture accumulation in OSB sheathing during winter in walls without a vapor retarder. In contrast, wintertime moisture accumulation was not significant with an interior kraft vapor retarder. Extruded polystyrene exterior insulation had a predictable effect on wall cavity temperature but a marginal impact on OSB moisture content in walls with vinyl siding and interior kraft vapor retarder. Hygrothermal simulations approximately captured the timing of seasonal changes in OSB moisture content, differences between north- and south-facing walls, and differences between walls with and without an interior kraft vapor retarder.
Highlights
The long-term moisture performance of exterior wall assemblies is a critical consideration for energy-efficient building envelopes
oriented strand board (OSB) moisture content is plotted in Figure 6 for wall configurations with and without a kraft vapor retarder for north and south orientations
Wintertime OSB moisture contents in north-facing walls with kraft facing remained below 15% MC with the exception of walls clad with manufactured stone veneer and stucco, which reached 16%–18% MC
Summary
The long-term moisture performance of exterior wall assemblies is a critical consideration for energy-efficient building envelopes. Designers and builders have many options in contemporary wood-frame wall construction for selecting materials such as exterior cladding, insulation, and vapor retarders. Recent changes to model energy codes, the 2012 International Energy Conservation Code (IECC) [1], have increased minimum insulation levels and tightened air leakage requirements for all light-frame wood wall systems (relative to the 2009 IECC [2]), and continuous exterior insulation may be an option or a requirement, depending on climate zone. With moisture performance increasingly becoming a concern and a design consideration, practical guidance is needed that will minimize the risk of moisture performance and durability problems in wood-frame buildings. Research-based design guidance is needed as various industry groups are advocating specific wall design solutions based on incomplete information
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
