Moisture-Related Durability of In-Service High-R Wall Assemblies in Pacific Northwest Climates

The Passive House program is becoming increasingly well-known in North America. This program aims to produce a superior thermal enclosure such that the space conditioning systems may be minimized, if not appreciably eliminated. Many Passive House designs use double-stud or thick wall enclosures. By adding significant thicknesses of cavity insulation, this approach provides a high level of thermal performance (R-value). However, the decreased heat flow through these walls reduces drying and can therefore place colder building components at risk of moisture damage. Constructing walls with exterior continuous insulation is a method that helps minimize these effects by warming critical layers, reducing potential condensation and moisture concerns.

This paper reports on two projects that assess the durability of these assemblies by comparing a 2 × 10 wood-framed wall with nominal exterior insulation in Portland, Oregon to a 2 × 10 wood-framed wall with an interior insulated service cavity in Victoria, British Columbia. The threshold of performance for these assemblies is discussed along with solutions to address potential concerns. Analysis of preliminary data shows that it is consistent with past research, and supports the conclusion that exterior insulation can improve durability relative to double-stud walls.

Note: This article was published in Proceedings of Buildings XIII, 2016. Copyright 2016 ASHRAE. Reprinted by permission at rdh.com. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about the Buildings XIII Conference Proceedings, visit http://web.ornl.gov/sci/buildings/2016/proceedings/.