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Design Strategies for Metal Wall and Roof Systems

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Design Strategies for Metal Wall and Roof Systems I S S U E 4/2018 VOLUME 35 NUMBER 4 Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Design Strategies for Metal Wall and Roof Systems Russell M. Sanders, AIA and Craig A. Hargrove, AIA LEED AP Y ears ago, prefabricated metal panel Materials and Finishes wall and roof systems did not find Most metal wall and roof systems are wide acceptance in high-end commer- proprietary, each manufacturer having cial applications. While these systems their own profiles, method of attach- were cost-effective, aesthetic percep- ment, and performance specifications. tions relegated them to large storage However, there are basic similarities in buildings, manufactur- these assemblies. ing facilities, and big box Metal systems come in a variety of stores. However, versatility, materials, with aluminum being the reliable performance, and most common due to its relative relatively low installed- durability, corrosion resistance, and costs have now made light weight. Aluminum panels are these systems attractive in available in flat plates – solid plate ap- more sophisticated appli- proximately one-eighth inch thick – or cations. Today, owners and composite panels, where foam insula- architects often collabo- tion is sandwiched between two layers rate to use these prod- of thin sheet aluminum. ucts in distinctive and aes- Steel is another commonly used ma- thetically innovative design terial. Strong and providing superior solutions. Manufacturers, impact resistance, steel is often se- recognizing an opportu- lected for facades in high-traffic areas nity, have expanded their Once considered budget cladding consigned to warehouses and for roofs that must span longer and industrial facilities, today’s metal panel systems are viable product lines with the aim distances between supports. However, options even for high-end projects. of amplifying product use steel’s strength means it is heavier than across a range of building other materials, necessitating more types. Of course, no building enclosure underlying structure to support the system is without design challenges load. Steel also requires a protective and considerations. coating to prevent deterioration due From structural and weather-proofing to corrosion. to energy efficiency, the longevity and Zinc panels are also becoming more performance of metal wall and roof popular because of the distinctive systems depends on an understanding appearance and durability afforded of material properties, code require- by the surface patina acquired during ments, and best practices. weathering. Patina formation occurs Russell M. Sanders, AIA, Executive Vice President and Senior Director, Technical Services, oversees all technical operations of Hoffmann Architects. Craig A. Hargrove, AIA, LEED AP, Senior Vice President and Director, Architecture, manages the firm’s Manhattan office, where his project teams meet tough design challenges. JOURNAL naturally in the presence of moisture protective coating of zinc applied to of protection must be included behind and carbon dioxide. Care should be steel that has a silver-gray appear- the panels, with consideration given taken where moisture may be pres- ance and is used to prevent corrosion to the way in which moisture that per- ent without sufficient carbon diox- of the underlying steel. Anodizing, an meates the cladding can be directed ide, such as at the underside of roof electrolytic process used on aluminum back to the exterior. Rain screens are panels, where condensation and other to increase its corrosion resistance, is a common form of open system that incidental moisture can cause cor- only available in a limited range of col- have become increasingly popular in rosion. This can also occur in areas ors (typically black, bronze, and silver). the last decade. that see significant amounts of water It’s important to remember that not How metal wall panel systems are accumulation, such as gutters. When all finishes are compatible with all installed and attached to the sub- using zinc panels, protective coatings materials. Even when an appropriate strate (and ultimately to the building applied to the at-risk surfaces should coating or paint is selected, application structure) is another defining element be considered. timing can significantly impact longev- of their design. The panels are most Copper is an extremely durable mate- ity. Typically, it is best to apply coatings commonly secured to a metal sub- rial option that generally does not and paints after the metal has been framing system consisting of “z” girts, require a protective coating; although, formed, to avoid hairline breaks in the metal studs, or proprietary configura- as with zinc, the use of such coat- material at bends. tions. This securement can be achieved ings at the underside of panels can in two ways: by use of “exposed” or be advisable under certain conditions. “concealed” fasteners. Uncoated copper also tends to stain With exposed fastener systems, panels adjacent surfaces and materials over “ Metal panel are attached to the substrate using time. systems provide fasteners that are screwed through Stainless steel never requires a pro- the panel and left exposed for ease of tective coating and provides a bright superior long- installation and aesthetic effect. While appearance. An aesthetic alternative the fasteners are often gasketed to term resource limit water infiltration, this method is is terne plate, stainless steel coated most commonly employed in open with an alloy that is over 99% tin. conservation. ” panel systems. Terne plate provides a weathered ap- pearance similar to zinc but, like zinc, Systems using concealed fasteners requires ventilation behind the panels employ clips to secure panel ends to to prevent pitting and corrosion. Prefabricated Metal Wall Systems the sub-framing system with bolts. This method can provide a clean, uninter- Depending on the material used, any Generally speaking, there are two rupted look to the metal panel system number of finishes and coatings may types of metal wall systems available: in either closed or open assemblies. be selected based on aesthetic and “closed” and “open.” performance requirements. Paints, such Closed assemblies (also called “barrier” Prefabricated Metal Roof Systems as fluoropolymers, enjoy wide use in or “face-sealed” systems) use the met- metal wall applications, as they come Prefabricated metal roof systems are al wall panels to resist the infiltration broadly defined as being either “hy- in a range of colors, and are resistant of weather (air and water) into the drokinetic” or “hydrostatic.” to fading. building. The metal wall panel system Hydrokinetic systems are not necessar- Porcelain enamel coatings fuse pow- is the air and moisture barrier of the ily “water-tight.” These assemblies shed dered glass to the metal surface at a facade. To achieve weather protection, water by moving it across their surface high temperature. Like fluoropolymers, the joints between the metal panels and off the roof as quickly as possible. they are durable and offer designers a must be sealed to form a comprehen- This requires that hydrokinetic roofs number of appearance options. sive barrier. have adequate pitch to effectively Many finishes have been developed Open systems, as the name implies, do move water and limit infiltration be- more for their protective properties not provide the primary protection neath panels. Since panel joints are not than for their appearance options. against air and moisture infiltration. In weather-tight, hydrokinetic systems re- Galvanizing, for instance, is a sacrificial these applications, a secondary means quire a substrate/underlayment system 2 VOLUME 35 NUMBER 4 to protect the interior of the building and inter-story drift. It’s important to against incidental moisture that finds remember that every component of its way beneath the roof surface. the system, from the substrate to the Hydrostatic systems, on the other fasteners to the panels themselves, hand, are water and air barriers that must be considered when designing form the primary protection at roof the cladding to meet the necessary level against weather infiltration into structural requirements. the building. Expansion Metal roof systems are also classified Metals will increase or decrease in size by their ability to span between struc- in response to a change in tempera- tural members. Architectural systems Leak investigation at this steel panel facade ture. A metal’s tendency to be affected pointed to faulty installation practices. cannot span long distances and re- in this way is defined as its thermal quire a continuous substrate for sup- expansion coefficient. The higher or solder for additional weather port. As a result, these assemblies are the coefficient, the more a material integrity. often hydrokinetic, since the substrate will expand or contract because of that is required for support can also Design Considerations a change in temperature. Zinc and act as a surface for an underlayment aluminum, for instance, have rela- protection system. Whether designing a prefabricated tively high coefficients (19.0 and 13.1, Structural systems can span between metal wall system, roof system, or respectively), while that of steel is rela- structural members without the as- both, the architect or engineer must tively low (7.0). This means that zinc address certain fundamental design sistance of a continuous substrate. The panels will expand nearly three times
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