Building codes help guarantee a building is sturdy and safe for occupants. All contractors and builders are familiar with the building codes, including the variations at the local level. Each of the different building codes has standards on which they are based. To prevent metal roofs from blowing off, there are specific standards and tests required for manufacturers to ensure the roof being installed meets the codes and will perform in adverse conditions.
Metal roof panels undergo specific tests to meet design requirements
Photo courtesy of Metallic Products
The 2018 International Building Code (IBC), International Residential Code (IRC) and the International Existing Building Code (IEBC) all reference the 2016 edition of the American Society of Civil Engineers’ (ASCE) 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, for wind load standards for structural building designs.
ASCE 7-16 is considered the standard method for determining wind loads on buildings and other structures, and includes provisions on wall and roof systems. It is also used to calculate wind uplift pressures on a roof, and the changes to the basic wind speed maps better reflect regional variation of wind speeds across the country. To ensure a correctly built metal roof, there are a variety of wind uplift tests manufacturers use to test their metal panel systems.
Design and Performance Requirements
There are three tests—UL 580, UL 1897 and ASTM E1592—that are used to determine a metal roof’s uplift rating. These tests are necessary to understand how a metal roof system can withstand both external and internal pressures, which is important when trying to meet design and performance requirements in projects.
Josh Jacobi, national manager/technical services at Petersen Aluminum Corp., Elk Grove Village, Ill., says, “To comply with the performance requirements of any particular project, the roof panels should be tested to prove that the specific assembly will perform to the design requirements of the project.”
Each of the specific tests establishes guidelines for the metal roofing panel assembly. “[The tests] provide an installation guideline in relation to substrates, material gauges, clip spacing, fastener type and panel profile,” Jacobi says. “For the panel assembly to perform properly, the installer should install all components in strict accordance with the specific testing specified in the contract documents.”
Depending upon the panel system, Jim Bush, vice president of sales and marketing at ATAS International Inc., Allentown, Pa., says they may be tested to one or all of the standards. “Using these industry and code adopted test procedures will aid in identifying performance capabilities of their individual systems that they offer. Each manufacturer should understand the factors that may affect performance of metal roof and wall panel systems in high wind events.”
Arbor Grande Clubhouse. Photo: hortonphotoinc.com, courtesy of Petersen Aluminum Corp.
Types of Wind Uplift Tests
UL 580 is the Standard for Tests for Uplift Resistance of Roof Assemblies. This test determines the uplift resistance of roof assemblies consisting of the roof deck and roof covering materials by evaluating the comparative resistance of roof assemblies to positive and negative pressures. The test evaluates the roof deck, how it’s attached to supports and the roof covering materials. For this test, testing agency Intertek evaluates the roofing assembly when subjected to sequences of static and oscillating pressures to pass each Class.
The UL 580 test procedure establishes minimum requirements in relation to a specific panel assembly. “A tested panel is listed by a specific UL construction number,” Jacobi explains. “It is important that each component listed in the particular UL construction number be present and installed as directed by the report.”
UL 1897, the Standard for Uplift Tests for Roof Covering Systems, provides uplift resistance data for evaluating the attachment of roof covering systems to roof decks by using differential air pressures. Applicable to any type of roofing system, the test evaluates the method of attachment of the roof covering system, including the base sheets, ply sheets, slip sheets, membranes, and, if used, insulation. While uplift pressures on a roofing system are dependent on many factors, this test method provides a comparative measure of the uplift resistance by means of static differential pressure.
ASCE 7 includes a method to calculate the uplift pressures on roof assemblies. Intertek notes this test is applicable for metal and composite shingles, single-ply membranes, standing seam metal panels and built-up roof applications.
ASTM E1592 is the Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference. McKeesport, Pa.-based Farabaugh Engineering and Testing says this test evaluates the structural performance of sheet metal panels and anchor-to-panel attachments for roof or siding systems under uniform static air pressure differences using a test chamber of support surface. Intertek notes this test method evaluates standing seam, trapezoidal, ribbed or corrugated metal panels in regards to uniform pressure applied to the single-skin construction or a single layer of multiple-skin construction.
Performance Data
Jacobi notes the ASTM E1592 test establishes performance values that are used in the ASCE 7 process to establish the performance of the panel specific to the building design. “These values are used when job-specific design calculations are requested by the designer,” he says.
As Bush adds, the tests themselves only provide performance data for the panel system itself or the actual system assembly, depending upon the actual test procedure. “One has to conduct engineering analysis based upon code requirements, which typically reference wind design standard ASCE 7 to identify the actual wind loads on the building,” he says. “Once those are established, the results from testing can ensure compliance with those design requirements.”
To adequately design a metal roofing system, it is essential for engineers and building designers to know the limits of the roofing system. “For through-fastened systems, these failures or limits are fairly straightforward—the panel itself may buckle under load, or the fasteners holding the system together can fail,” explains Stephen Knight, PE, engineering manager for McElroy Metal, Bossier City, La. “Both of these types of failures can be calculated using AISI standards for cold-formed steel, and the IBC does allow them to be calculated accordingly.”
“In the case of through-fastened system,” Knight adds, “wind uplift tests are not necessary so long as the manufacturer has performed calculations on the panel capacities in accordance with the referenced IBC standards.”
Standing seam panels, however, have limits that are far more complex. Knight says the intricate locking and/or clipping connection mechanisms make predicting the failure point difficult to analytically calculate. “Furthermore, their failure methods aren’t limited to only buckling or fastener failure; there are many failures specific to standing seam systems subject to uplift that will and can occur before buckling or fastener failures typically occur.”
“For instance,” Knight continues, “the two panels could separate from one another at the seam location, the clip tab could slip out from the panel seam, or, in two-piece clip systems, the top tab of a clip could break loose from the bottom tab of the clip system. For these reasons, it’s critically important that standing seam systems be uplift tested to find these failure points to properly design the roof system.”
To properly withstand wind speed, a metal roof system needs to be properly installed. Bush explains that in review of varied metal roof failures after high wind events in both hurricane and non-hurricane events, the Metal Construction Association (MCA) identified that a lack of attention to detail in the perimeter flashings contributed to the failures of entire roof systems. “MCA, after various research testing, embarked on establishing a test method to verify performance of edge flashings used in metal roof systems,” Bush says. “Modeled after edge performance testing for flat roofing systems as identified in the building codes, the pending ANSI/MCA FTS-1 2019 Test Method for Wind Resistance of Flashings Used with Metal Roof Systems was developed. This test standard will aid in identifying proper design requirements for the critical edge flashings to properly handle the wind pressures in addition to the metal panels themselves.”
Center for Coastal and Deltaic Solutions. Photo: hortonphotoinc.com, courtesy of Petersen Aluminum Corp.
An Analytic Tool
When it comes to the UL 580, UL 1897 and ASTM E1592 tests, Knight says the one of the most important things to understand is that they are not to be used in lieu of a site-specific analysis by a design professional, but are a tool to be used for the analysis.
Knight notes there’s really no replacement for a quality set of shop drawings from either the manufacturer or a knowledgeable professional that has reviewed and sealed by the engineer responsible for the roofing system. “UL listings also do a great job of listing the specifics, so make sure you’ve obtained an actual copy of the UL listing,” he says. “Otherwise, many manufacturers’ technical departments are happy to help. McElroy Metal, for instance, will run preliminary calculations for your building site free of charge.”
“The most significant change that ASCE 7-16 will present is an increased focus on the wind pressures in areas of the roof where forces are the worst,” Knight explains. “Specifically, the corners of the roofs are subject to pressures much higher than other areas, and these corner pressures are getting even higher—although this may not be significant for many areas of the country, coastal projects will see more stringent designs than ever before.”
“The industry has established these guidelines over the course of the past 30 years and most all commercial projects require one of these tests to establish performance guidelines,” Jacobi says.
“To compete in our industry today, a manufacturer must have testing on its panels to meet the architect’s design protocols. There are occasions where some panel profiles have not been tested but it is rare. Most architects, designers and consultants require proof of testing or design calculations during the submittal process. This has aided in minimizing the use of any product that does not have the required testing.”
