For rainscreen-style overcladding systems—whether insulated metal panel, panelized EIFS, terra cotta, or fiber cement board—the system generally is supported by a light-gauge metal subframe of either galvanized steel or aluminum. The subframe is cantilevered from the backup with a rail system
or with adjustable brackets. In consultation with structural engineers, the sub-framing system must be designed to address dead load, wind load, seismic concerns, thermal expansion and contraction, and deflection for different backup conditions.
Regarding cost impacts, masonry overcladding solutions tend to be driven by budget-conscious solutions. For this reason, variations in costs associated with particular products or assembly components tend to be marginal, in the author’s experience.
Moving onto thermal bridging, metal frames, brackets, and rail systems do carry the potential for thermal transfer. Metal brackets and subframes attached directly to the masonry backup tend to conduct cold temperatures, contributing to the building’s heat loss. For these reasons, many manufacturers produce components made from low-thermal-conducting metals, and systems incorporated with thermal breaks. Whether or not the building team specifies products from one of these manufacturers, it is critical to design an assembly that includes thermal breaks in the subframe system to avoid thermal bridging, and to enhance the enclosure’s thermal performance.
Face-sealed systems and climate region appropriateness
Regarding assembly design for management of water vapor and moisture, it is important to consider whether face-sealed systems are appropriate as an overcladding solution in any climate region. Whether a given face-sealed solution is stucco, EIFS, or system such as metal paneling with joints sealed with caulk or similar, these systems for exterior overcladding create challenges for enclosure design teams, who understand there must be a way for moisture to drain or dry—as they are not ideal in most climates.
The recommended and appropriate uses of face-sealed overcladding systems would be generally for low-rise buildings in very or relatively dry climates with lots of sun and little rain. Even in these scenarios there could be benefits for designing and specifying one of the open, drained system types recommended for many climate regions, whether conventional metal panels, fiber cement panel, or EIFS.
Notes
1 See the article by McKelvey, Wilson, Copley, and Foster, “A Sustainable Repurposing of the Aging Facility,” published by BEST5 Technical Committee, April 16, 2018, www.brikbase.org/content/sustainable-repurposing-aging-facility.
2 Read the paper by Anis, Wagdy, FAIA, “Air Barrier Systems in Buildings,” Whole Building Design Guide, www.wbdg.org/resources/air-barrier-systems-buildings.
3 Visit the EIFS Industry Members Association, “Standards,” www.eima.com/technical/standards.
Author
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