Are Metal Panels An Ideal Low-Slope Roofing Material?

Many large, commercial, low-rise buildings often don’t benefit from steeply-sloped roofs the way residences and small commercial buildings might. This is because a steep roof slope would add unwanted height and unnecessary construction cost. Buildings like warehouses, retail stores, etc. are more appropriately built with low-slope roofing, commonly known as “flat roofs”. The National Roofing Contractors Association (NRCA) defines low-slope roofs as those with “a slope at or less than 3:12″. Anything steeper qualifies as a “high-slope roof”. With this in mind, let’s look at some key points to consider when designing and constructing a low-slope roof.

MBCI Low-Slope Roofing

 Low-Slope Roofing Materials

When it comes to selecting low-slope roofing products, there are generally three fundamental choices:

  • Asphalt/ Bituminuous Products: The traditional commercial roofing norm for many years, the use of asphalt/bituminous products has dwindled as newer, more appealing options have emerged.
  • Flexible Membrane Roofing: This roofing material can be made from a variety of types of plastic/polymer-based materials (commonly known as EPDM, TPO, PVC, etc.). Rolls of the chosen membrane are laid out on the roof structure and secured in place either with mechanical fasteners (screws with large washers) or with a continuous layer of adhesive.
  • Metal Roofing: Sometimes overlooked, metal roofing is suitable for different roof slopes. Many metal roofs that use standing-seam systems are rated for use with a pitch as low as ½:12.

When considering which type of roofing material to use for a building project, there are a number of significant differences that illustrate why metal roofing is often the ideal choice.

Engineered For Superior Performance

Standing-seam metal roofing is made specifically for use on low-slope roofs as it meets a number of performance requirements:

  • Water resistance: Precipitation doesn’t penetrate through metal or through the standing seams where the metal panels join together. This is why they can tolerate such low slopes, allowing the water to drain away slowly and predictably without leakage.
  • Rigidity: The rigid nature of metal means that there is less opportunity for ponding (standing water). This is not always the case with asphalt/bituminous or membrane roofing systems.
  • Drainage: Metal roofs carry water to the building’s edge toward gutters and downspouts that carry it away from the building. Other roofing systems rely on drainage piped inside the building. This takes up space and has the potential to leak water inside the building and cause damage.
  • Wind Resistance: Standardized uplift testing shows that metal roofing performs as well or better in extreme weather than mechanically-fastened or fully-adhered membrane systems.
  • Durability: The most cited advantage of metal roofing is its long-term strength and durability. Engineered design and use of high-quality coatings ensures a longer lifespan—50 years or more. In contrast, other roofing types typically feature lifespan ratings of 20 or 30 years.
  • Puncture Resistance: Low-slope metal roofing is more puncture-resistant than asphalt/bituminous or membrane roofing. This makes it better able to tolerate foot traffic, hail and other puncture-inducing hazards.
  • Construction/ Installation Ease: Metal roofing panels are custom-made to suit specific building sizes and end uses. This customization typically means it takes less time to place and install metal roofing in the field. Further, metal panels can tolerate a wide range of temperatures and weather conditions and still install and perform as intended. Low-slope roofs are also safer to walk on with less risk of slips, falls and other hazards.

Cost-Effectiveness

Using metal roofing on low-slope roofing systems can be cost effective in a number of ways:

  • Fewer labor hours as a result of the ease of installation saves money during construction.
  • Competitive material costs, particularly if the metal roofing is part of a total metal building package from a single manufacturer.
  • Minimal maintenance requirements and aversion to rusting, mold growth and decay that save the building owner money over time.

This all adds up to a very favorable life-cycle cost.

The performance, cost-effectiveness and life-cycle benefits of metal roofing panels make them a viable option for low-slope roofing systems. Manufacturers like MBCI can help you select the right metal roofing products and provide information and resources to help ensure proper installation.

View examples of low-slope metal roofing projects and contact your local MBCI representative to start your project today.

Appropriate Standing Seam Clips for Roof Panels

Part of the beauty and appeal of standing seam metal roofs is that the fasteners holding the metal panels in place are concealed. That gives the roof its clean, continuous appearance that is often desirable, but it also avoids the issue of potential roof leaks around exposed through-fasteners. Concealed fastening doesn’t mean that there aren’t any fasteners, though, it just means they are installed out of sight – underneath the panels. The industry standard approach is to use a metal clip that fits over the edge of a panel and that is secured with a screw type fastener to the structure or substrate below. Then it is covered by an adjacent panel or trim. The important thing to know is that not all panel clips are made the same – for good reasons.

What determines the type of panel clip to use? Here are the most common things to keep in mind:

The Manufacturer

Each manufacturer of metal roofing typically has a range of metal panel types, profiles, and brands that have their own traits and characteristics. As such, they need clips to match and fit with the manufactured panels. Hence, the first place to start with panel clip selection, is for the roofing manufacturer to be clear on the options and choices available that are compatible with their roofing products.

Building Size and Type

Fixed clips (left) and floating clips (right) are two of the most commonly used types of clips.
Fixed clips (left) and floating clips (right) are two commonly used types of clips.

Manufactured metal buildings that include metal roofing commonly use very predictable, coordinated systems. Accordingly, a standard, one piece, “utility clip” is commonly used, primarily for snap together roof panels, on metal buildings that do not exceed certain widths causing undue expansion and contraction. One piece clips allow the roofing panels to expand and contract within the clip profile, but there are limits based on the amount of movement tolerated. Alternatively, in projects where the roofing is attached to something other than a metal building frame or where standing seams are used to secure the panels together, it is advisable to use a two-piece or “floating” clip. In these cases, a base piece is secured to the structure or substrate and the clip fits both into the base and over the roofing panel where it is seamed or folded into the vertical leg of the panel. Using this approach, the clip expands and contracts directly with the metal panel thus moving across the base and keeping the roofing attached.

Insulation

Roof insulation comes in different thicknesses, appropriately so for different climate zones and different roof designs. Since energy codes require at least some of the insulation to fit between the underside of the metal roofing panel and the structure (i.e. above the metal roofing purlins), the metal panel clip needs to be the right height to reach the full height of the insulation up to the top of the roof panel. Hence, manufacturers offer different sizes and heights of panel clips designed to work with different heights of insulation. In many cases, they also recommend the use of a thermal spacer underneath the clip to separate it thermally from the steel structure below. Note that the thermal spacer thickness is dependent on the insulation thickness over the steel purlin only, not the thickness of any insulation under the purlin.

A certified installer should install your standing seam roof to ensure proper installation of clips.
A certified installer should install your standing seam roof to ensure proper installation of clips.

Other Factors

The panel clips connect the roof panels to the roof structure, so they need to be installed in a manner that allows them to do that job under normal and demanding circumstances. The driving issue in this case is not keeping the panel down, but preventing it from blowing off in a strong wind. Therefore, a structural engineer or other design professional may need to determine the proper spacing of the clips, the type and size of fasteners (i.e. screws) to use, or similar important details. Similarly, the proper installation of clips so that they seat and nest the way they are intended, means that qualified and certified installers / erectors should be used. In this way, roofing crews with the needed experience and training can help assure that the whole roofing system, including the panel clips, are installed properly.

To find out more about the most appropriate panel clips to use on a metal roof that you are involved with, contact your local MBCI representative.

Standard Testing for Metal Roofing – Part 1: Structural Performance and Uplift Resistance

When selecting a metal roofing product, there is an expectation that it will perform as intended over the life of the building. But what assures building owners, code officials, or design professionals that a product will in fact perform as promised? This question often comes up in building product discussions and the accepted way to answer it is to subject the products to physical testing. The type of testing is usually very specific to the product based on protocols and procedures developed by independent agencies such as Underwriters Laboratories (UL), ASTM International, or others. Manufacturers typically submit their products to independent testing labs who follow these standard test procedures. Once testing has concluded, they report the results back to the manufacturer. These results then show whether the product meets stated performance criteria or not. If not, the manufacturer can re-design and re-test until it does and then make the final results available to the public.

For metal roofing, a series of relevant and important tests are typically performed. In this blog, we will look at two of them related to structural performance and wind uplift.

ASTM E1592

The structural integrity of metal roofing is crucial given the various natural forces that can be imposed on the materials. Effects from wind, snow, or other conditions can compromise its integrity. Accordingly, the ASTM Committee E06 on Performance of Buildings (including sub-committee E06.57 on Performance of Metal Roof Systems) has developed ASTM E1592 “Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference”. While the standard acknowledges the use of computation (i.e. calculations) to determine the basic structural capacity of most metal products, it also points out that some conditions are outside of the scope of computational analysis and hence need to be tested.

The standard describes a test method with “optional apparatus and procedures for use in evaluating the structural performance of a given (metal) system for a range of support spacings or for confirming the structural performance of a specific installation”. As such, it is very specific both to metal roofing and its installation. This test method uses imposed air pressure not to look at air leakage but simply to determine structural reactions. It consists of three steps:

1. Sealing the test specimen into or against one face of a test chamber

2. Supplying air to, or exhausting air from, the chamber at the rate required to maintain the test pressure difference across the specimen

3. Observing, measuring, and recording the deflection, deformations, and nature of any failures of principal or critical elements of the panel profile or members of the anchor system

The test needs to be performed with enough variation to produce a load deformation curve of the metal and account for typical edge restraint (fastening) representative of field conditions.

Manufacturers need to submit different products that are tested at least once at two different span lengths between supports. Standing seam roof panels are typically tested at a 5’-0” and 1’-0” span. Spans between the two tested spans can be interpolated. The result is a table of tested loading results that can be compared to code required or engineered design loading to then determine if the selected material and spacing are adequate for the project needs or if another product or spacing is needed.

MBCI's metal roofing products undergo a series of tests to ensure maximum resistance and performance.
MBCI’s metal roofing products undergo a series of tests to ensure maximum resistance and performance.

UL 580

The ASTM E1592 test is focused on the structural integrity of metal panels. It also uses positive and negative air pressure in a static (i.e. non-moving) condition to determine performance. There is also a separate concern about how metal roofing will perform in a dynamic condition as would be expected in a windy condition where wind gusts can ebb and flow erratically. In that regard, a separate test developed jointly between Underwriters Laboratories (UL) and the American National Standards Institute (ANSI) looks at the ability of roofing to resist being blown off a building due to wind. Known as ANSI/UL 580 “Standard for Tests for Uplift Resistance of Roof Assemblies”, it has become the recognized means to identify and classify the suitability of roofing for different wind conditions – low to high.

This test is also specific in its scope and intent stating that it “evaluates the roof deck, its attachment to supports, and roof covering materials”. It also points out that it is not intended to test special roof conditions, main or secondary structural supports, or deterioration of roofing. The standard prescribes in considerable detail the type of test chamber that needs to be constructed and used for the testing which includes three sections: “a top section to create a uniform vacuum, a center section in which the roof assembly (i.e. deck, attachment, and roofing) is constructed, and a bottom section to create uniform positive pressure”. The test procedure is then based on placing the roof assembly into the test chamber and subjecting it to a prescribed sequence of 5 phases of oscillating positive and negative pressure cycles (simulating dynamic wind conditions) over 80 minutes of total testing.

There are four wind uplift classifications obtainable for a tested assembly based on the test assembly retaining its attachment, integrity and without any permanent damage. These include Class 15, Class 30, Class 60, and Class 90. Each class has its own requirements for test pressures with increasing pressure as the class number increases. Higher class numbers indicate increasing levels of wind uplift resistance. Note, that to obtain a Class 60 rating, the tested assembly must pass the Class 30 test then be immediately subjected to the Class 60 test sequence. Similarly, to obtain a Class 90 rating, the tested assembly must first pass both the Class 30 and 60 tests. Metal roofing manufacturers who want their roofing products tested and classified under UL 580 must pair them with standard roof deck and fastening materials. Hence most have many different tests performed and results reported accordingly.

When reviewing metal roofing options, it is comforting to know that most manufacturers have tested their products and designed them to meet or exceed minimum requirements. To find out more about tested results of products you may be considering, contact your local MBCI representative or see the MBCI website and select the “testing” tab under a selected product.

Quality Control Accreditation Programs for Metal Roofing Products

Performance-based building product testing and accreditation is a critical piece of just about every aspect of construction—affecting everyone from the manufacturer to the installer and ultimately to the owner and occupant. These certifications ensure real-world property loss will be prevented and provides protection when certified products are installed correctly.

With roofing being such a vital part of any building project, roofing manufacturers must take certifications for roofing products (in this case, metal roofing products) very seriously. Below, we’ll give a brief overview of the main certifications that we—and other metal roofing companies—test to and are audited for in order for the overseeing bodies to confirm that we’re producing what we’re testing it to. In the simplest terms, these specifications, such as UL or FM, will give the contractor peace of mind that he or she can provide what is spec’d.

At MBCI, we have several certifications through which we have ratings. These include:

1. UL (Underwriters Laboratories).

UL certifies roofing materials and roof assemblies for fire performance, hail resistance and/or resistance to wind uplift. Roof deck assemblies are investigated for performance under internal fire exposures and for uplift resistance. MBCI does a good deal of testing and we have UL constructions for many of our roofing products. We get the UL construction number, impact ratings and fire ratings. UL does quarterly audits in the manufacturing areas to make sure that we’re producing the panels the way we test.

2. IAS (International Accreditation Service) certification.

IAS accreditation programs are based on recognized national and international standards that ensure acceptance of its accreditations. To meet this standard, MBCI is “Part B” of the process, as we are responsible for the components. The auditor comes in to certify that we do what we say we do. Once IAS accreditation requirements are met, the company receives a certificate of accreditation.

3. FM (Factory Mutual) approvals.

MBCI has three roofing products that are FM approved for wind uplift standards, hail resistance, internal and external fire ratings. For each, we test the product and FM comes out yearly to do an audit.

Accreditation
This is an example of FM wind uplift testing.

4. Dade County roofing product approvals.

Miami-Dade and Broward Counties are classified as High Velocity Hurricane Zones (HVHZ), which are rated as 150 mph plus winds. It is Florida’s highest rating. An updated testing approval process has been instituted for building products and materials used in these counties. The purpose is to mitigate damage caused by wind-borne debris resulting from hurricane-force winds. MBCI does testing and this stringent certification is applicable for anything that ships into Dade County or Broward County in Florida. Product Notice of Acceptance can be located on the Miami-Dade website for roof and wall panel systems that are Dade County approved.

Safety and performance are the most important goals. All in all, these certifications ensure that we, the manufacturer, are doing our job and that customers are getting everything they’re paying for. For more information on MBCI’s product testing, please contact a sales representative.

Evolution of the Metal Building Components Industry

Metal building components have been in use ever since iron and steel became commonly available during the 1800s. However, coordinated metal building components as we know them today really got their start during the 1900s, with a lot of significant developments happening just in the past 40 years. Here’s a quick overview:

1970s:

During the 1970s, the emerging metal buildings industry was primarily focused on providing pre-engineered solutions for commercial, industrial, and agricultural customers, mostly in the range of 10,000-square-foot buildings or less. The use of lighter-weight, tapered-end steel sections and bolted end-plate connections was beginning to be developed for widespread use, based on industry research. The development of technology that allowed for new methods of steel fabrication created growth for existing companies and helped new ones to form, such as MBCI in 1976. The energy crisis of the time brought interest in creating better insulation solutions.

Metal Building Components Plant Location
MBCI Lubbock, Texas Plant

1980s:

This was a period of growth along with the rest of the construction world. New plants and facilities were opening up in response to growing customer and market needs. New coating technologies were coming available that provided  better corrosion resistance and allowed for more customers to consider using metal buildings. Technical research into wind loading for walls and wind uplift for roofs brought updated means and methods to address these critical structural engineering conditions.

1990s:

During this decade, the volume of metal buildings and tons of steel processed nearly doubled. More building types were being constructed out of metal building components as architects, engineers, and owners saw the flexibility, time savings, and cost efficiencies involved. Retail facilities, offices, even schools started to incorporate metal buildings and their components into their planning and construction. With this growth and expansion, technical issues such as snow loads and employee issues such as OSHA regulations were hot topics of research and focus.

Metal Building Components featuring Legacy Junior High
Legacy Junior High School Featuring PBU Metal Panels

2000s:

With strong momentum and growing success around the country, the industry began to offer more-diverse product offerings and components. Insulated metal sandwich panels with both interior and exterior finishes became more common. New roofing finishes and appearances became available. Structural research into seismic effects on metal buildings was conducted in response to California earthquakes, and solutions were determined. Further work was done on energy performance of metal buildings in response to energy codes and customer requirements. Additional work was undertaken on updated engineering guidelines for tapered structural members and exterior wall and roof finishes and styles. This included the use of horizontal instead of vertical siding systems and smooth-surface solutions.

A Look at Today in the Metal Building Components Industry:

The metal building industry has clearly evolved and come a long way from somewhat humble beginnings. Today, full systems or components can be found in a wide range of buildings types, creating highly attractive solutions that are often not recognized as metal buildings. Continued industry research helps manufacturers provide high-quality products that meet the demands of the larger building industry. Continued collaboration and partnerships are helping to foster diversified product offerings and new market penetrations. Overall, the past 40 years or so have been just the beginning – the future of the industry looks strong, and prospects remain high for continued growth.

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.

Choosing the Right Type of Standing Seam Roof (SSR)

When it comes to specifying standing seam roofs, one type doesn’t fit all. While a standing seam metal roof system can be one of the most durable and weather-tight roof systems available in the industry, its benefits can be negated if you fail to understand the details in application parameters of the specific system. Do your research, though, and for your next design that requires an aesthetically pleasing and structurally sound metal roofing system, you can choose with confidence the standing seam metal roof system that suits your project to a tee.

How to identify a good standing seam roof system

A good standing seam roof system is one that can satisfy both the project’s specific design criteria and adhere to building code standards. Standing seam profiles can include those that are utilitarian or architectural in nature, are of numerous widths and profiles and have varying seam joinery (e.g., snap or field seamed).

Why specify a standing seam metal roof system

When properly installed, standing seam metal roof systems are an extremely effective and long-lasting material choice. Key advantages include:

  • Weather-tight roofing system
  • Can be engineered to withstand high winds (150 mph and higher)
  • Class A Fire-resistance rating from UL
  • Class 4 Impact-resistance rating from UL
  • Long service life—up to 60 years
  • Lightweight
  • Special clips designed to accommodate thermal roof expansion and contraction and various thicknesses of fiberglass insulation

Matching the roof system to the project

In basic terms, there are four unique styles of metal standing seam panels: Double lock seam, symmetrical seam, one-piece snap-lock interlock and two-piece snap-lock interlock. These styles can be further delineated by seam shape or profile, i.e. trapezoidal rib, vertical rib, square rib and tee rib. The choice of the rib profile, as well as the rib spacing is generally an aesthetic preference of the designer. Knowing which style will best suit a given situation will help ensure a successful installation.

Popular Standing Seam Metal Panels

Double Lock Standing Seam
Shown: MBCI Double-Lok®

One-Piece Snap Lock Interlock Standing Seam
Shown: MBCI LokSeam®

Two-piece Snap Lock Interlock Standing Seam
Shown: MBCI Craftsman™

Some criteria to consider are roof slope, roof run (distance from eave to ridge), weather conditions (such as ice or snow) and architectural features, i.e. hips, valleys, dormers, parapet walls, etc.

For instance, if your project has a roof slope of 1/2:12 you will need to ensure the product being installed is approved for this low pitch. In this case, you would likely use a “double lock” or mechanically “field-seamed” panel. You also want to ensure that all details are able to provide for a weather-tight seal even if temporarily submerged during a heavy rain. Field-seamed panels are also the best choice in areas that experience heavy ice and snow.

Additionally, it is imperative to recognize complicated design details that should be carefully specified and reviewed regardless of the roof slope. Design conditions that require special attention include: roof transitions, dead valleys, dormers, eave offsets, ridge offsets and offsets in parapet walls.

It cannot be overstated that you should always consult a metal roofing manufacturer about the capabilities of the standing seam metal roof system, including what warranties are available, prior to specifying it.

Browse the standing seam product manual for more information.

Design and testing

Familiarize yourself with wind uplift testing as prescribed by Underwriters Laboratories (UL-90 – 580 Test) and ASTM E-1592.

For more information on standing seam metal roofing, visit MBCI’s CE course on the topic: http://www.bdcuniversity.com/standing-seam-metal-roofing

Myths About Metal Roofing: Heat, Wind and Lightning

Properly detailed and installed metal roofing is one of the most resilient, lasting, efficient and attractive kinds of roofing systems for commercial and institutional buildings. Yet there are plenty of questions about metal roofing, and building teams often find time in project meetings to address the most common, recurring topics and myths.

Facts vs Myths About Metal Roofing

I call these “mythbuster meetings,” because many of the questions are fabrications – concerns arising from less savvy professionals or from competitive “selling points.” Among the most prevalent untruths:

Myth about Wind Uplift

Myth: Wind uplift affects metal roofing more than other roofing types.

Reality: While the noncontinuous nature of metal roof attachments makes them susceptible to wind uplift concerns, most roofing types are prone to similar effects. ASCE/SEI calculations for wind loading and FEMA studies of storm areas have shown that properly applied metal roofing outlasts other roof assemblies during hurricanes and tornados.

Building geometry affects how well the roof survives, regardless of roof type. Engineering determines how many insulation board fasteners are needed, and the optimal and safest distances between clips for standing seam systems at corners and perimeters, where the forces are greatest. The interlocking or “active fastening” helps metal roofing pass severe wind and uplift tests including ASTM E1592, UL 580 and UL 1897, and the Miami/Dade County codes, according to a report from Stanford University.

Myth about Heat

Myth: Metal panels get hotter and have more thermal bridging because metal conducts heat so well.

Reality: Depending upon the surface finish, metal roofing can “provide enhanced energy efficiency with its solar reflectance and infrared emittance properties […] to meet the climate requirements of the building,” according to the Stanford University paper and research highlighted by the Cool Metal Roofing Coalition.

As compared to other roofing types, metal roofing tends to be highly reflective and is available with high emissivity. Insulated metal roofing panels have foam insulation that delivers R-values up to R-8.515 per inch thickness and total roof U-factors that exceed those of many other roofing types, helping projects meet strict energy code rules.

Myth about Lightning

Myth: Metal roofs are more likely to get hit by lighting than any other roof types.

Reality: That is bunk; simply untrue. You can read my detailed blog on the subject, or for serious mythbusters refer to the Metal Construction Association’s Technical Bulletin MCA13a, which gives a full and authoritative overview.

As the MCA summarizes, “Because metal roofing is an electrical conductor and a noncombustible material, the risks associated with its use and behavior during a lightning event make it the most desirable construction available.” That’s right: The best option for lightning risks.

I hope some of the above information provided insight and assurance about building with metal roofs. If you have any additional questions or concerns, submit them here to our technical experts.

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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