Useful Tool: FM Wind Ratings RoofNav

The concept of testing materials and assemblies in buildings has been around since the late 1800s, when John R. Freeman initiated Factory Mutual Laboratories (now known as FM Approvals) to test fire protection systems. Since then, the use of FM-approved building components and assemblies has become recognized as an accepted safety standard for insurance companies, building inspectors, design professionals, and building owners. In the case of roofing systems, FM is particularly well known for determining how roofing performs not only for fire, but also for high wind. In fact, it is unique among other testing laboratories in the way that it performs wind uplift testing – it uses full-scale roof sections measuring 12 feet by 24 feet to obtain an accurate view of expected real-world performance. Further, it tests not only individual products, but full assemblies. In the case of metal roofing, for example, that would include the metal roofing panels, the fasteners (e.g., screws), EPDM washers, seam sealant, and any insulation, all as attached to a specific roof deck or structure.

Is it Approved by FM?

To find out if a roofing product or assembly has been approved by FM based on its independent testing, the best place to look is on the FM roof navigation website, known as RoofNav. Registration is free and offers access to FM’s fully searchable, comprehensive database.

How to Use FM RoofNav

Here is a quick overview on using the website:

  • My Projects Tab: The opening page is on the “My Projects” tab, which welcomes the user to RoofNav and lets a registered user save and return to specific data searches.
  • Product Search Tab: The second tab at the top of the web page is labeled “Product Search,” and allows a user to enter information under search criteria based on a manufacturing company and/or a trade name, as well as selectable roofing categories (such as “cover”) and subcategories (such as “composite panel cover”). Clicking on the “search result” sub-tab will show all of the corresponding products tested, and their approved uses. If a specific manufacturer, such as MBCI, is entered in the search criteria, the results will show only for that manufacturer. Clicking on a particular result will open detailed specifications and information for that product.
  • System Search Tab: If a particular system is being sought, such as a fastening system or vapor retarder system, the “search criteria” portion under this tab can help narrow things down by name, type, and products.
  • Assembly Search Tab: Since the real performance of a roof is based not on a single product or system, but an entire assembly, it is possible to search either by “classifications,” using basic criteria, or by “specifications,” which allow a detailed roof assembly to be created. Either method will produce a list of “search results” that can be clicked on to get more details. This is likely the most useful tab when looking to determine if a total roof assembly will meet the wind uplift rating needed for a particular project, but it does require that the proper details are input.

The website also contains a number of very helpful ways to assist a user. A tab for a “ratings calculator” allows flexibility in the amount of information entered; a tab for “reference materials” provides drop-down assistance with tools such as a “quick-start guide.” Links for “help,” “support,” and “training” appear at the top of the page, along with a quick-search portal where a known FM assembly number can be entered and found directly.

The RoofNav tool is a great resource for anyone who wants to find out test-result information about any one or a series of roofing products, systems, or assemblies, and can be a go-to resource for contractors, designers, and specifiers of roofing systems of all types.

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.

Using Wind Clamps to Improve Wind Uplift on Standing Seam Metal Roofs

Among the most important factors to account for when specifying a standing seam metal roof are wind control and wind uplift. It is imperative to take the necessary measures to ensure the safety and efficacy of the metal roof. The wind clamp—an extruded piece of aluminum that is placed on the panel seams at clip locations—is one accessory that can be used to improve wind uplift characteristics on metal roofs, delivering substantial time and cost savings as these devices help mitigate risk of wind uplift and improve overall wind design.

Panel Deflection
Standing Seam Panel Deflection as a Result of Wind Uplift

Why Use a Wind Clamp

A typical failure mode of a standing seam metal roof panel is the clip top pulling out of the panel seam when the panels are subjected to high winds.  With a standard install of a standing seam panel, the seams just fold into each other. With enough pressure, wind will force seams to come apart—be it a vertical failure, horizontal movement of the seam or from clip disengagement. The clip top can then pull out of the panel seam.

The wind clamp resists the panel seam being opened, allowing for higher uplift loads. The purpose of wind clamps, in fact, is to prevent Windclamprszdfailures at the seam openings due to any deflection of the panel. The wind clamps provide more strength, thereby dramatically improving wind uplift performance.

The clamp is installed over the panel seam at clip locations, in the edge and corner zones of the roof.  This allows the roof to resist the higher wind pressures in these zones, usually eliminating the need for additional purlins or joists. On large roofs, the savings can be substantial.

Another benefit is shorter installation time. Since additional purlins or joists are typically not required at the edge or corner zones of the roof, the building can be erected faster.

Choosing Wind Clamps

When choosing the type of wind clamp, it is important to consider the type of panel and the special features of the clamps. MBCI, for example, uses S-5!’s patented wind clamps, which work for two panel types—Ultra-Dek® and Double-Lok®. The S-5! wind clamps do not penetrate the steel, thereby eliminating the risks of corrosion and water leakage that can be introduced by a hole in the steel. Since the screws are hidden from the weather elements, it helps to maintain waterproofing.

Quantitative Difference with Wind Clamps

One of the biggest benefits of using wind clamps in the edge and corner zones is that usage minimizes the quantity of purlins needed, resulting in substantial cost savings. For example, let’s look at a comparison using MBCI’s Double-Lok 24” – 24 ga. panels with and without wind clamps.Chart for blog image

In this example:

  1. The use of wind clamps in the edge and corner zones eliminated 3,800 linear feet of purlins.
  2. Assuming 8” x 2-1/2” Zee 14 ga. purlins were used, there would be a cost savings of $10,400.

Conclusion

Utilizing wind clamps to protect the investment of a standing seam metal roof can increase strength, make installation faster and lower overall cost.

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