Understanding Wind Uplift Testing for Standing Seam Roof Systems

When properly designed and installed, a standing seam metal roof system provides the building owner with long-term dependability and value. Standing seam roof systems fulfill requirements for durability and protection against just about any type of weather situation, and they excel in high winds. Overall, they have outstanding performance records.

In the most severe weather conditions, wind pressure can force panels to deflect. This causes the seams to open and the panels to shift in failure mode. Typical failure occurs at the corners and edge zones. As a result, standing seam metal roofs must meet certain standards and testing criteria.

While there are many performance tests out there, the ASTM E 1592 is considered most reliable for the design of standing seam panels.  It is the standard test method for structural performance of sheet metal roof and siding systems by uniform static air pressure differences.

The most common wind testing standards include:

  • Underwriters Laboratories (UL) 580
  • Underwriters Laboratories (UL) 1897
  • Factory Mutual (FM) Global Standard 4471
  • American Society for Testing and Materials (ASTM) E 1592
UL 580 Wind Test
Uplift resistance testing with UL 580 test platform.

UL 580

The UL 580 rating determines the uplift resistance of roof assemblies. The test evaluates the roof panel, panel clips, fasteners and the substrate.

Test Method

  • A 10-foot by 10-foot sample of roofing material is installed onto a test platform. The edges are then sealed with closely spaced fasteners and two purlins in the interior.
  • Next, the sample is subjected to a static uplift pressure for a 5-minute period and an oscillating pressure in 10 second intervals over a 60-minute period.

Considerations

  • UL 580 is a pass/fail test and does not specifically determine wind resistance of the panel assembly.
  • It only tests over a specific substrate at a certain clip/fastener spacing.
  • The test standard will not indicate how strong the panel assembly is under load.
  • Most importantly, the test does not simulate real conditions.

UL 1897

The UL 1897 wind test is a continuation of UL 580, and is the standard for uplift tests for roof covering systems. The purpose of this test is to gain uplift resistance data for the panel assembly, and evaluate the attachment of the roof covering systems to the roof decks.

Test Method

  • Utilizing a test chamber, this test is conducted by either pulling a vacuum above the assembly or by pressurizing an air bag placed loosely between the deck and the roof covering.
  • The test is run to failure, and the results are reported as the highest uplift pressure achieved prior to failure (in psf).

Considerations

  • UL 1897 does not consider the strength of the roof deck.
  • The method does not necessarily simulate the actual dynamic uplift pressures encountered by roofing systems.

FM Global Standard 4471

FM 4471, Approval Standard for Class 1 Panel Roofs, states the requirements for meeting the criteria for fire, wind, foot traffic and hail damage resistance.

The test sets performance requirements for panel roofs, which includes all components necessary for installation of the panel roof assembly as a whole. This includes the potential for fire spread on the underside and exterior of the roof panel. It also measures ability to resist simulated wind uplift resistance while maintaining adequate strength and durability.

Test Method

  • FM 4471 utilizes a 12-foot by 24-foot section, including the connecting fasteners and clips used in the field. The panels are subjected to increased wind pressures until the assembly fails.
  • The ratings are stated as 1-60, 1-90, 1-120, and so on, referring to wind pressure in pounds per square foot (psf).
  • This rating is used to apply a classification to roof panels. Class 1 roof panels are rated at 1-90. A safety factor of 2 means the maximum allowable design load is 45 psf.

Considerations

  • FM Global is a non-profit scientific research and testing organization that deals with commercial and industrial property insurance.
  • For roofing projects where FM insurance is required, project designers should work closely with the roofing manufacturer to ensure the roofing system complies with FM requirements.

ASTM E 1592

This test method provides a standard for structural performance under uniform static air pressure differences, and is run to failure to find the ultimate uplift load capacity. This test measures both panels and anchors. ASTM E 1592 is not a pass/fail test; it merely shows how a roof performs under uniform static load.

Test Method

  • A 5-panel-wide sample (10 feet) by 25-foot length is subjected to pressure from underneath to imitate wind load. The sample has intermediate purlin support at varied intervals and covers several spans.
  • The pressure is applied to identify slowly developing failures such as seam separations, and to determine the ultimate failure load of the standing seam roof system.
ASTM 1592 Wind Uplift Testing
MBCI research and development team performs ASTM 1592 wind uplift tests. The wind pressure forces the panels to deflect, pushing the center of the panel above the seams.

Testing for Reliable Design

ASTM E 1592 was developed to account for the many complexities of evaluating uplift properties of metal roofing. The test method “provides a standard procedure to evaluate or confirm structural performance under uniform static air pressure difference. This procedure is intended to represent the effects of uniform loads on exterior building surface elements.” (https://www.astm.org/Standards/E1592.htm)

In conclusion, while all of the standardized test protocols mentioned above were established to determine uplift capacities of roof assemblies, only the ASTM E 1592 uplift test is considered reliable enough for the design of standing seam roof panels. Among its key differentiators, the test takes into consideration the roof’s flexibility, changes in shape occurring under air pressure, and it measures both metal panels and their anchors.

Wind Designs for Metal Roofs

One of the most important requirements for metal roof installation is ensuring that a roof stays in place when the wind blows.  The core concept is that the roof’s wind resistance needs to be greater than the wind loads acting on a building’s roof.  Wind resistance is most commonly determined by a physical test; wind loads are calculated.

Calculating Wind Loads

Wind loads are based on the design wind speed (which is based on the geographic location of the building), height of the roof, exposure category, roof type, enclosure classification and risk category.  The height of the roof, and exposure and risk categories are factors that are used to convert design wind speed to an uplift pressure.  Wind speed maps and the rules to calculate wind pressures are found in Section 1609, Wind Loads, in the 2012 or 2015 IBC.  The information is based on an engineering standard written by The American Society of Civil Engineers, “ASCE 7-10, Minimum Design Loads for Buildings and Other Structures.”Wind Uplift Testing_2

Defining Exposure Risk Category

Exposure categories relate to the characteristics of the ground, such as urban and suburban areas or open terrain with some obstructions or flat areas like open water.  There are 4 risk categories.  Category I is low risk to humans, such as agricultural facilities. Category III includes, for example, buildings for public assembly, colleges and universities, and water treatment facilities.  Category IV includes essential facilities like hospitals and police stations.  Category II is everything else—most roofs are Category II. A building shall be classified as enclosed, open or partially enclosed. The enclosure classification is used to determine the internal pressure coefficients used to calculate design roof pressures.

Determining Wind Pressures

Contractors should work with a structural engineer or the metal panel manufacturer to determine the wind pressures for each roofing project.  Wind pressures are determined for the field of the roof, the perimeters and the corners, where loads are largest.  Only after determining the design pressures can the appropriate metal panel roof system and attachment requirements be designed.

Testing Uplift Resistance

Physical tests are the most common method to determine uplift resistance.  Panel width and profile, metal type and thickness, clip type and frequency, type and number of fasteners, and the roof deck contribute to the uplift resistance of every metal panel roof system.  Metal panel roof systems installed over solid substrates (with concealed clips or through-fastened) can be designed using the following test standards: FM 4471, ASTM E 1592, UL 580, or UL 1897.  Metal panels installed over open framing can be designed using either ASTM E 1592 or FM 4471.  Manufacturers run these tests; uplift resistance data is available for most metal panel roof systems.  Installers can get this data directly from manufacturers or from web-based listing services provided by FM and UL.

Designing a Legal Metal Roof System

Wind loads and wind resistance information is necessary to verify code compliance.  Get it for every project you install!  Using systems that not only have been tested to the correct tests, but using systems that have uplift resistance greater than the design loads is key to a successful installation, and quite frankly, key to installing legal roof systems.

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