9:00 am - 10:00 am | Room: Owens Corning Room | Session Chair: Bomani Khemet

Evaluating Building Air Tightness

Airtightness And Water Penetration Resistance Of Exterior Insulated Wall Assemblies

As the construction industry moves toward more energy-efficient buildings, installing continuous exterior insulation is an effective way to achieve higher thermal performance wall assemblies. When designed appropriately, an exterior insulated wall assembly can provide high effective R-values without compromising usable interior space. These thermal performance benefits of exterior insulated assemblies are well understood within the building industry, but other benefits, particularly those associated with air and water control, are often overlooked, and in some cases questioned due to the presence of cladding attachments through the exterior insulation which penetrate the sheathing membrane, potentially creating paths for air and water leakage.

This paper presents a summary of recent work completed by the authors investigating the performance of exterior insulated wall assemblies with respect to air and water control. In particular, the performance of these assemblies when using different insulation types (Rockwool Comfortboard 110TM and extruded polystyrene (XPS)), back-up walls (wood vs steel stud), cladding attachments (long screws through wood strapping or hat-track, vertical Z-girt, Z-clips with continuous vertical furring channel), and rainscreen cladding with open-joints (cladding option providing an increased exposure of water reaching the insulation and sheathing membrane) is investigated using quantitative airtightness testing, qualitative smoke tracer testing, and water penetration testing incorporating indicator dyes. These techniques are developed based on standardized testing techniques including ASTM E2357, ASTM E547, and ASTM E1186, with modifications made to better reflect observed failure conditions in the field. A unique drainage balance apparatus was also developed to measure the amount of water which drains on the various drainage surfaces within a wall assembly, as a means of determining the relative risk reduction provided by measures such as exterior insulation.

The results of this testing provide key information to inform design decisions for building enclosures, and also work to provide additional evidence as to the benefits of exterior insulation, beyond the widely discussed thermal performance considerations. By working to support the development of a more holistic understanding of exterior insulated assembly performance, the findings of this study support the broader application of exterior insulation as part of high-performance building design.

Lorne Ricketts, RDH Building Science

Working across a wide spectrum of RDH’s core practice areas in his roles as a consultant, researcher, and educator, Lorne is able to leverage his multifaceted expertise to identify optimal solutions to complex building science problems. Lorne’s typical projects include world-class architecture, industry-leading energy efficiency, and cutting-edge building technologies. In addition to his work with RDH, Lorne also passes on his knowledge to the next generation of engineers as an Adjunct Professor at the University of British Columbia, where he teaches building science in the Department of Civil Engineering.