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 appearance 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

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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 considerations. While manufacturers panels of these systems derive their as much, and aluminum nearly twice as can be instrumental in this effort, a strength in a variety of ways, includ- much, as steel. design professional with knowledge of ing the use of stronger metals, thicker the building enclosure is often indis- Accommodation for such movement panels, raised panel ends, intermedi- pensable. The following is a brief list must be built into the design to avoid ate ribs, and/or corrugation in the of some of the issues to be addressed issues such as buckling, fastener failure, panel profile. Since structural systems during design. and deterioration of system integrity. require no substrate, they are often Movement tolerance can be achieved hydrostatic. Structure in a variety of ways, including slot- Regardless of the system selected, One of the primary considerations for ting of fastener openings, limiting the metal roof panels are typically in- building enclosure assemblies is their length of panel sections, and/or incor- terlocked, or “seamed,” together. structural integrity. Facade and roof porating expansion joints. Examples of interlocking methods cladding systems must have the ability include flat seams, standing seams, and to resist a variety of forces to which Weather Integrity battens. In hydrostatic applications, they may be subjected, including grav- Weather integrity – the ability of seams may also be sealed using sealant ity, seismic load, wind load, deflection, roof and facade assemblies to resist

For this military training camp, standing-seam aluminum roofs with a high-performance resin A zinc facade system gives this rooftop coating met fast-track project demands, while offering durability in the harsh seaside climate. mechanical room a sleek, modern look.

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the infiltration of air and moisture Common Problems be considered to limit the deleterious – is essential. As discussed earlier, effects of ice. these systems can be either “closed” Steep-sloped roofs must include ad- (hydrostatic) or “open” (hydroki- equately sized and configured gutters, netic). In either case, consideration of leaders, and downspouts to remove weather integrity and accommoda- water that collects on the surface or tion for moisture are necessary design substrate. Gutters can be external or challenges. “built-in” (concealed). In prefabricated metal facades, “closed” Lastly, “weather integrity” includes not or face-sealed barrier systems rely on just resistance to moisture, but to air. Condensation a primary seal between joints – often Most governing authorities now have seam tape or an elastomeric sealant specific requirements limiting the flow system – to provide weather integrity. of air through the building enclosure. These primary seals between panels As with moisture protection, closed have a shorter life expectancy than systems rely on the metal panel sys- the panels themselves and are there- tem to resist such air flow, while open fore the first part of the system to fail. systems depend on a substrate barrier Consequently, they present an ongoing for preventing air infiltration. maintenance concern. Thermal Performance In “open” facade systems, the substrate Corrosion behind the panels (often exterior- Building enclosures must meet increas- grade sheathing with a water-resistant ingly stringent requirements regard- coating or cladding over metal studs) ing energy and thermal performance. acts as the primary protection against Metal systems benefit from having a air and water infiltration. In such cases, low thermal mass; however, they are water that will inevitably find its way not very good insulators. Therefore, behind the metal panels must be the use of insulation within the as- channeled to the exterior of the build- sembly must be a consideration during through a system of flashing and ing design. Typically, the insulation is Movement and water intrusion weeping. Even with such protection installed between the metal panels in place, the volume of water that can and the underlying substrate and is infiltrate behind the panels should be comprised of mineral wool or foam limited. plastics such as extruded polystyrene or polyisocyanurate. Hydrostatic roof systems rely on the pitch of the roof and the integrity of Energy performance requirements the panel seams (often enhanced with vary depending on climate zone and seam tape, sealant, or solder) to keep the model building code adopted in a water from infiltrating the building. region. In New York City, for instance, Peeling coatings Hydrokinetic systems also limit water roof assemblies must include insulation infiltration through roof-pitch and the with a thermal resistance of at least integrity of seams, but do not elimi- R-30. Metal-framed walls must include nate it. In such systems, an underlay- R-7.5 of continuous insulation plus an ment consisting of, for instance, #30 additional R-13 of insulation between felt paper and a slip sheet (building pa- the sub-framing studs. per), must be applied to the substrate As much of prefabricated metal panel to protect the building interior. In cer- wall and roof systems are, by defini- tain climates, membrane protection at tion, metal, linear and point transmit- the roof perimeter extending at least tances (thermal shorts that transfer Discoloration and staining 24 inches onto the building must also energy between the interior to the

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exterior of the building) should be considered and eliminated to the TESTING and MOCK-UPS greatest extent possible. Such mea- of sures also help reduce the poten- METAL PANEL SYSTEMS tial for condensation within the assemblies. The complexity and performance requirements of enclosure systems, in general, and Because of the need to attach the prefabricated metal panel systems, in particu- panels to the substrate, often by lar, make mock-ups and testing a worthwhile means of metal girts, insulation within consideration. The following is a summary of the assembly is frequently interrupted, options available at various stages of design causing thermal shorts and reducing and construction. the overall efficiency of the wall or roof. In such cases, isolators, typically in At the design phase, manufacturer’s test data and technical documentation the form of lightweight, highly porous should be provided. This allows the design team either to confirm that the coatings called aerogels, can be applied proposed assembly can meet the various project requirements or to identify to the sub-framing system to reduce key information that might be missing. Incomplete technical documentation the transfer of energy along its surface. from the manufacturer may be an indication that the system is not appropriate for the application, or that additional testing is required to validate its use. Condensation During pre-construction, a Visual Mock-Up (VMU) allows all stakeholders to The potential for condensation to observe a representative sample of the proposed system and approve it for develop within the facade or roof aesthetics and design intent. The VMU should enable the team to confirm system must be considered during overall appearance, proportions, color, and texture as well as the effectiveness design and measures taken to limit the of attempts to limit undesirable visual characteristics, such as “telegraphing” deleterious effects of such moisture. and “oil-canning.” A VMU can be a project-specific mock-up fabricated on- or While providing adequate ventilation off-site, or it can be a similar system installed on a previous project, as identi- behind or beneath the panels is some- fied by the design team and manufacturer. times sufficient, a correctly designed A Performance Mock-Up (PMU) is a representative sample of the enclosure and installed vapor retarder is often assembly installed at an off-site testing facility, where approved test methods necessary. can ascertain the system’s conformance with performance requirements, Sound Attenuation including structural integrity, thermal resistance, acoustics, and air and water resistance. PMU testing typically takes place concurrently with construction. Typically, metal panel systems are not very effective at mitigating the In short, a manufacturer’s published data provide an overview of a wall or transfer of sound. During design, the roof assembly’s performance, but it is no substitute for independent verifi- STC (“sound transmission class”) or cation testing. Pre-construction VMU testing establishes design parameters, OITC (“outdoor/indoor transmission while in-situ PMU testing during construction, for issues such as air and class”) rating for the project should be water resistance, provides validation that the system meets performance established and the sound attenuation requirements. properties of the system identified. Measures can then be taken to en- hance the properties of the assembly through, for instance, the incorpora- tion of additional insulation or air cavities. Combustibility The use of certain building materials within a prefabricated metal panel enclosure system (such as foam plas- Mock-ups provide a representative sample Fans simulating high winds are used to evaluate design and performance. for dynamic water testing. tics as insulation or a core material in

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A LOOK INSIDE Metal Walls and Roofs

Installed in the 1990s, this metal cladding system consists of This aluminum standing-seam roof system is installed over ice painted steel composite panels with a paper honeycomb core. Rigid dam membrane, as well as stiffening ribs at the flat of each panel to insulation, inboard of the panels, provides thermal resistance. minimize oil canning and telegraphing of structural members.

(continued from page 5) composite metal panels) may pres- appearance on the surface of the drainage system, the potential for ent issues with combustibility. The panel. accumulation of snow and ice in design professional should reference amounts large enough to be a danger Snow and Ice Accumulation the applicable code for requirements still exists. Consideration should be governing the combustibility of such In certain climates, the potential for given to incorporating an appropri- assemblies. Keep in mind that it is not snow and ice to build up on roofs is a ate snow guard system into the roof just the assembly itself that must con- concern. Such accumulations can dam- design to limit this possibility. As with form to these requirements; detailing age perimeter assemblies and fall from a roof’s drainage system, calculations of the transition to adjacent building the building in amounts large enough must be performed to affirm that the systems (such as between floors, at to be a hazard. system is restraining snow and ice in a windows and doors, and between manner that will promote gradual re- Improper drainage design can often walls and roofs) must be considered lease of runoff over time and limit ac- lead to such build-up at roof edges. to achieve the required fire protection cumulation in any one area of the roof. Gutters and leaders that are too across the entire exterior envelope. Ideally, such systems should not pen- small or configured incorrectly cannot etrate the metal roof panels, to reduce Appearance adequately remove runoff before it the possibility of water infiltration. While this article focuses on the refreezes, resulting in large accumula- Proper attic ventilation helps to pre- technical aspects of metal wall and tions of ice at gutters and eaves that vent ice dam formation at eaves, allevi- roof systems, appearance is nonethe- can damage perimeter assemblies and ating strain on the snow guard system less an essential design consideration. infiltrate the building through a pro- and reducing the possibility of leaks. Technical considerations can affect that cess known as “ice jacking”. During de- overall appearance and care should be sign, calculations should be performed Dissimilar Metals to ensure that the roof’s drainage taken to avoid choices that can have a Different metals that come in contact system is adequately sized and that detrimental effect on aesthetics. with each other within the assembly gutters are configured in accordance Consult with manufacturers regard- can lead to corrosion, through galvanic with recognized standards such as ing the potential for issues such as action, and to staining, through water the Sheet Metal and Air Conditioning telegraphing, where the outline of runoff. When the potential for galvanic Contractors’ National Association underlying stiffeners or fasteners action exists, dissimilar metals should appear on the surface of the metal Architectural Sheet Metal Manual. be separated by a protective coating panel, or oil-canning, a wavy or dimpled Even with an adequately designed or other method.

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Metal Wall and Roof Systems Crowne Plaza Times Square New York, New York Today’s metal panel exterior wall and Consultation for New Composite roof assemblies must meet many more demands than the inexpensive, Aluminum Panel Entrance Canopy quickly installed sheet metal cladding Smithsonian Institution that enclosed warehouses and indus- Udvar-Hazy Center trial facilities of the mid- to late 20th Chantilly, Virginia century. With metal panel systems of- Investigation of Aluminum Insulated fering an expanded range of features Panel Facade and Design for 7W21 Flatiron Luxury Apartments and options, examples of metal-clad Replacement with Aluminum Panel structures can be found in nearly all in New York, New York. Building Envelope Consultation for Zinc Wall and Roof Systems. Rainscreen building types. U.S. Social Security Administration Owners and designers of these build- Union Station National Computer Center Washington, District of Columbia ings face a range of code require- Woodlawn, Maryland Terne-Coated Stainless Steel Panel Roof ments with which the panelized Repairs to Insulated Aluminum Wall assemblies must comply. In-depth Condition Assessment Panel System understanding of how best to satisfy Camp Niantic regulations for thermal performance, Regional Training Institute weather integrity, combustibility, sus- Connecticut Army National Guard tainability, and more, is essential. Niantic, Connecticut Hoffmann Architects has assessed, Replacement of Asphalt Shingle Roofs designed, and overseen repair or with Standing-Seam Aluminum Alloy construction of metal wall and roof Sheet Metal Roofs systems at diverse facilities, including: Federal Reserve Bank of New York Loria Center for the History of Art East Rutherford, New Jersey MedImmune Manufacturing Center in Yale University Condition Assessment for Steel Frederick, Maryland. Leak Investigation at New Haven, Connecticut Composite Insulated Panel Wall System Coated Insulated Steel Panel Facade. Building Envelope Design & Construction Smithsonian Institution Review, including Zinc Panel Wall System Garber Facility AstraZeneca Suitland, Maryland Decentralized Material Control Center Leak Investigation at Coated Structural Frederick, Maryland Standing-Seam Metal Panel Roof and Insulated Metal Panel Facade Leak Insulated Metal Panel Facade Consultation Allen-Stevenson School Lexington Armory New York, New York New York, New York Snow Accumulation Remediation at Rockland Psychiatric Center in Redesign of Snow Guard System for Standing-Seam Metal Facade and Roof Orangeburg, New York. Ice Buildup Mitigation Copper Panel Roof Systems at Metal Standing-Seam and Clay Tile Roofs.

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Hoffmann Architects, Inc. 2321 Whitney Avenue Hamden, CT 06518

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(continued from page 6) Achieving Design Goals JOURNAL is a publication of Hoffmann Prefabricated metal panel assemblies Architects, Inc., specialists in the were long considered affordable, but rehabilitation of building exteriors. The inefficient and aesthetically unappeal- firm’s work focuses on existing structures, diagnosing and resolving prob- ing, building enclosure systems and lems within roofs, facades, windows, were relegated predominantly to waterproofing materials, structural sys- large storage, retail, or manufacturing tems, plazas/terraces, parking garages, facilities. However, within the last thirty and historic and landmark structures. We also provide consulting services for years, improvements in the aesthetics new building construction, as well as and performance of metal wall and litigation and claim support. roof systems, combined with an in- For address changes, free subscriptions, novative design community, have made or information on the topics discussed them viable options in high-end com- in this issue, contact our Marketing mercial projects, offering a wide range Department at 800-239-6665, Metal facade systems come in a variety of of options and appearances. [email protected], or: materials, including aluminum, copper, stainless steel, and zinc, pictured here. Given the complexities of building 2321 Whitney Avenue Hamden, CT 06518 enclosure systems and the ever-more- 203-239-6660 Sustainability stringent code requirements governing their performance, leaving the design 1040 Avenue of the Americas, Ste. 14C It’s important to note that many New York, NY 10018 premanufactured metal panel sys- of even proprietary systems largely 212-789-9915 tems include anywhere from 25 to to a manufacturer can be ill-advised. 95 percent recycled material. At the The selection of a qualified enclosure 2711 Jefferson Davis Highway, Ste. 333 specialist, and that design professional’s Arlington, VA 22202 end of their lifespan, most metal 703-253-9800 panel systems can be recycled again, consideration of a host of project- providing superior long-term resource specific design parameters, is essen- www.hoffarch.com conservation as compared with other tial to delivering a successful project Editor/Production: Alison Hoffmann materials. outcome.

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