Metal Roofing Wind Uplift and Resistance Testing

Understanding Testing Methods Helps Roofers Select the Right Panels for the Job

By Dan Brownell

Metal roofing has earned a reputation as a material with superior structural strength, so it has increasingly become the preferred choice for residential, commercial, and industrial roofing, especially in areas prone to high winds or hurricanes.  

Metal roofing is tested for a number of performance characteristics besides its ability to withstand wind damage, such as hardness, reflectivity, chalking, color change, air infiltration, chemical resistance, fire resistance, and salt spray corrosion resistance. Two of the most important tests, however, concern “wind uplift” and “wind resistance,” since they help determine whether a metal roof will actually remain intact during bad weather. 

Wind uplift and wind resistance are related but have an important distinction. “Wind uplift” refers to a roof’s ability to stay attached to a roof without being compromised. The term “wind resistance,” however, is broader in that it also includes a roofing system’s ability to withstand impact damage from hail and flying debris.

The Importance of Understanding the Tests and Ratings

Knowing how the various tests are conducted and how they vary is important in choosing the correct panel for each job and for the installer to earn the customer’s trust and confidence. “Metal panel testing and ratings are necessary to comply with some local building code requirements,” said Shannon Clark, of True Metal Supply. “So, understanding testing and ratings helps to ensure the installer is choosing the right product based on the project’s requirements, the local building code requirements, and the geographical needs (such as high wind areas, hurricane-prone locations, etc.) This also helps establish the installer’s credibility. Understanding testing and ratings enables installers to effectively communicate the value of quality assurance to their customers,” Clark added. “By being knowledgeable about various tests — such as fire resistance, impact durability, and weather performance — builders can explain how these ratings ensure the longevity, safety, and overall performance of the roofing system. This helps build trust with customers, reassuring them that the selected materials have been rigorously evaluated to meet high industry standards, ultimately protecting their investment.”

While at least a basic knowledge of ratings is essential, a deeper grasp is much better. “Think of it like tires,” said Scott Steele of Best Buy Metals. “They are all round, have tread, a specific size, and they go on rims. But what about speed ratings, the belt material used in construction, the hardness of the rubber, the profile height? There’s a lot that goes into the level of understanding needed in order to make an informed recommendation for each client. It’s also possible that new testing methods, or codes that require new testing methods, will occur. 

Having a builder or contractor that is associated with or member of an organization like the Metal Roofing Alliance (MRA) or others can help keep them better informed,” he said. “Alternatively, if the roofing contractor or general contractor is partnered with a manufacturer, they will benefit from their collective knowledge of testing results as well as their organizational memberships that keep knowledge of test methods and results up to date on a regional and national scale.”

It’s up to the manufacturers to pursue testing and ratings. “Manufacturers will choose what tests they’d like to have done, and they have the responsibility to provide the approval report to the customer,” Clark said. “The manufacturer should also explain the testing and how it relates to different projects — this may be via website, printed materials, etc.” 

Commonly Used Testing Agencies

The three most common agencies that metal manufacturers use for wind uplift or design pressure (DP) testing are The American Society for Testing & Materials (ASTM), Underwriter Laboratories (UL), and Factory Mutual (FM). The ASTM and UL standards are the most widely used. The FM standard was developed by Factory Mutual, an insurance company that requires its customers to use its standards. The company does all testing in-house with company employees, as FM has a strong incentive to decrease losses due to damage claims. As a result, these tests are much more expensive than ASTM and UL tests, so they aren’t used as much.

Wind Uplift Tests

Section 1504 of the International Building Code (2021 version) covers four wind uplift test standards for metal roofing: ASTM E1592, UL 580, UL 1897, and FM 4474. The four tests have different testing methods and standards as outlined below.

ASTM E1592 (Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference)

The ASTM E1592 standard tests panel spans between 1 and 5 feet, and sometimes up to 8 feet, on an open frame assembly, to the point of failure. 

UL 580 (Standard for Tests for Uplift Resistance of Roof Assemblies)

UL 580 places the roof assembly in an enclosed 10-foot x 10-foot chamber. Suction is applied to the top of the panels while upward pressure is applied to the bottom to simulate simultaneous negative and positive pressure. The tests are conducted at 30 psf, 60 psf, and 90 psf increments. At 90 psf, the pressure oscillates between 90 and 105 psf. Depending on the psf at which the panel fails, it is assigned a rating of Class 15, Class 30, Class 60, or Class 90, earning the Class designation below the psf point of failure. In other words, if a panel fails at 70 psf, it’s assigned Class 60. The testing stops at Class 90, even if the panel doesn’t reach the point of failure.

The UL 580 test uses a safety factor of 2.0, which means that the Class number is double the actual limit allowed on a roof. So a Class 90 (which includes a 105 psf oscillating pressure) would have an allowable limit of 52.5 psf.

UL 1897 (Standard for Uplift Tests for Roof Covering Systems)

UL 580 testing stops at Class 90, with a 52.5 psf allowable limit. This is too low for some roof applications, so UL 1897 is designed to test to a higher allowable psf level. It’s a continuation of the UL 580 test that can be performed immediately after the test is completed, so the UL 1897 test can be done using the same test panel. The test pressures are increased until the point of failure. 

FM 4474 (Evaluating the Simulated Wind Uplift Resistance of Roof Assemblies Using Static Positive and/or Negative Differential Pressures)

FM 4474 tests panel systems to the point of failure, but the testing is done in smaller increments of 15 psf. As mentioned earlier, FM tests are much more expensive than ASTM and UL tests, so they aren’t used as often. 

TAS 125 (Testing Application Standard 125)

TAS 125 testing is designed for metal roofing used in High Velocity Hurricane Zone (HVHZ) areas, such as Miami-Dade, Florida. In the state of Florida, all metal roofing panels are required to have a Florida Product Approval. The specific product approval required is determined by the wind zone in which the building is located. Florida has four wind zones, which are listed in ASCE 7-98. 

Wind Zone 1: 110-119 mph

Wind Zone 2: 120-129 mph

Wind Zone 3: 130-139 mph and within 1 mile of coastline

Wind Zone 4: Winds above 140 mph

Impact Damage Tests

As previously mentioned, the term “wind resistance” is more encompassing than “wind uplift” because it includes a roofing system’s ability to withstand impact damage from hail and flying debris. Common tests for evaluating a roof system’s susceptibility to impact damage are the UL2218 and ASTM E1886.

UL2218 Impact Test 

With the UL2218 test, the roofing system must “show no tearing, fracturing, cracking, splitting, rupture, crazing or other evidence of opening.” If it tears or fractures, it fails the test. The following chart lists the comparative susceptibility to damage from four sizes of steel balls dropped from four heights and lists the panel’s corresponding Class rating. Some insurance companies offer lower premiums for Class 4 metal roofing.

Class Steel Ball Diameter Drop Distance 

Class 1:  1-/14” diameter 12’0

Class 2:  1-1/2” diameter 15’

Class 3:   1-3/4” diameter 17’

Class 4:   2” diameter 20’

ASTM E1886

The ASTM E1886 test evaluates a roofing system’s susceptibility to impact from missiles, such as falling tree limbs and other wind-driven debris and simultaneously tests the system to oscillating wind pressures. This combined testing helps ensure a roofing system can withstand impact damage and reduce or prevent leaking.

Conclusion

These carefully designed and controlled tests lead to ratings that help roofers provide customers with quality roofing that meets the requirements of their specific buildings. Not only does this protect the structures, but also lowers risk of injury or death of occupants enduring extreme storms. RB

Calculating Minimum Wind Uplift Design Loads for Specific Buildings 

Test results can vary widely from one roofing panel system to another. What might be sufficient for one particular building may not be for another. The roof design needed to meet a building code or a particular design parameter depends on a number of factors, including site conditions, wind speeds, building exposure category, roof slope, mean roof height of the building, and roof zone. 

Roof Zones

The wind uplift resistance of a panel can vary by roof zone, or where it’s located on a roof. There are three roof zones, designated Zones 1, 2, and 3.

Zone 1: Field or interior areas of the roof more than 4 feet from edge or ridges of roof. These areas experience the lowest wind pressures of the three zones.

Zone 2: Edge or end areas within 4 feet of edge or ridges of roof. These areas experience pressures between Zones 1 and 3. 

Zone 3: Corners of the roof. These areas experience the highest wind pressures.

ASCE 7 (American Society of Civil Engineers Minimum Design Loads for Building and Other Structures)

ASCE 7 is a standard used for calculating the requirements for a specific roof using an algorithm. Each building needs its own calculation, because each structure is unique and the factors affecting calculations can change. For example, the terrain surrounding a building can evolve over time, which could change wind patterns. Surrounding buildings may have been erected nearby on previously open fields or a wooded area may have been cleared, which may alter uplift ratings. The required rating may have increased since the original roof was attached, so no assumptions should be made and a new load calculated for each roofing job. RB

Supplier & Builder Resources

• Ace Clamp (aceclamp.com)

• Best Buy Metals (bestbuymetals.com)

• Chief Buildings (chiefbuildings.com)

• Coated Metals Group (cmgmetals.com)

• Drexel Metals (drexmet.com)

• Englert (englertinc.com)

• Everlast Roofing (everlastroofing.com)

• Flack Global Metals (flackglobalmetals.com)

• Frontier Metal (frontiermetal.biz)

• Hixwood (hixwood.com)

• Lester Buildings (lesterbuildings.com)

• Levi’s Building Components (levisbuildingcomponents.com)

• Little Harvey’s ([email protected])

• McElroy Metal (mcelroymetal.com)

• Metal Exteriors (metalexteriors.com)

• PAC-CLAD Peterson (pac-clad.com)

• Progressive Metals (progressivemetals.com)

• ProVia (provia.com)

• Steel Dynamics (steeldynamics.com)

• True Metal Supply (truemetalsupply.com)

• United Steel Supply (unitedsteelsupply.com)

The Benefits of a Deep Understanding

If builders lack a deep comprehension of testing methodologies and rating systems, they may struggle to:

• Communicate effectively: Builder may misinterpret or oversimplify test results, which can lead to inaccurate product representations and customer dissatisfaction.

• Recommend appropriate products: Without a clear understanding of panel performance, builders may choose suboptimal materials for specific climates/weather conditions or building conditions.

• Manage customer expectations: No one ever wants to over promise based on incomplete knowledge of product capabilities. It’s not good for business and can harm the reputation of the metal roofing manufacturer as well.

Conversely, a strong grasp of metal roofing testing empowers builders to:

• Match products to customer needs: By understanding the significance of different ratings, builders (or their metal roofing manufacturing partner) can recommend materials that align with specific customer requirements, such as durability, aesthetics, or energy efficiency.

• Build trust and credibility: Demonstrating expertise enhances customer confidence and loyalty.

• Manage risks: A thorough understanding of product limitations can help builders mitigate potential issues and avoid costly callbacks.

—Scott Steele, Best Buy Metals