Effects of Exterior Insulation on Moisture Performance of Wood-Frame Walls in the Pacific Northwest: Measurements and Hygrothermal Modeling

Author: Glass, Samuel V.; Yeh, Borjen; Herzog, Benjamin J.; 

Date: 2016

Source: 3rd Residential Building Design & Construction Conference - March 2-3, 2016 at Penn State, University Park PHRC.psu.edu 2016 

Publication Series: Scientific Journal (JRNL)

Description: Continuous exterior insulation on above-grade walls is becoming more common in many parts of North America. It is generally accepted that exterior insulation provides advantages for energy performance, by reducing thermal bridging, and for moisture performance, by warming the wood structural members, thereby reducing the potential for wintertime moisture accumulation. However, the effects of vaportight rigid foam insulation on the drying capability of the wall systems are not fully understood. In this study, temperature and moisture conditions in north-facing and south-facing wall assemblies with vapor-open and vapor-tight exterior insulation were monitored in a natural exposure test facility in the Marine 4 Climate Zone over a two-year period. The wall assemblies included interior gypsum board with latex primer and paint, 2×4 framing with nominal R-13 batt insulation, 11 mm (7/16 in.) oriented strand board, nominal R-5 exterior insulation, and white-color vinyl siding. Exterior insulation was either extruded polystyrene or mineral wool. Measurements and hygrothermal simulations indicated that walls with extruded polystyrene and mineral wool exterior insulation in north and south orientations perform similarly. Moisture content in wood framing and oriented strand board were within safe levels.

Keywords: exterior insulation, continuous insulation, energy performance, building envelope, building enclosure, hygrothermal modeling, Pacific Northwest, wood-frame walls, drying capability, wall systems, temperature, moisture, insulation

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Glass, Samuel V.; Yeh, Borjen; Herzog, Benjamin J. 2016. Effects of exterior insulation on moisture performance of wood-frame walls in the Pacific Northwest: Measurements and hygrothermal modeling. 3rd Residential Building Design and Construction Conference, 2-3 March 2016. Penn State, University Park PHRC.psu.edu 2016.

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