RoofViews

Building Science

Roof Design Considerations When Incorporating Solar

By Jennifer Keegan

August 27, 2019

Solar panels

If photovoltaic systems (solar arrays) were installed on all the commercial buildings in the US with roofs over 5,000 sq. ft., they are estimated to provide enough energy to power nearly 60% of the total commercial electricity demand. Commercial rooftops are an appealing option as a platform for installing solar arrays to support energy conservation and generation, as well as corporate and community energy initiatives. However, it is important to remember that the roof's primary function is to protect the building and its contents from the elements.

When considering rooftop solar, the roof system should be designed to have an equivalent or longer lifespan than that of the solar arrays. Whether it's a new roof with solar arrays or will have solar arrays installed in the near future, or it's an existing roof that will receive solar, there are many important considerations for roof system design and panel layout.

Roof System Durability

Solar arrays have a useful economic life of up to 25+ years. For commercial rooftop solar, it is often cost-prohibitive to remove the solar arrays, install a new roof and reinstall the solar arrays. Therefore, the best time to install a rooftop solar system is right after a new roof installation or right after a building is newly constructed. The key issue here is that the roof system should have an expected useful life that matches or exceeds the expected economic life of the solar array. To specify a roof system that is as durable as the solar array, designers should consider the following:

  • Adhered roof membranes with higher heat resistance and greater mil thickness;
  • Incorporation of a cover board;
  • Use of high compressive strength rigid insulation; and
  • Roof system warranty or guarantee that exceeds the life expectancy of the solar arrays

Roof Membranes

By their nature, reflective roof membranes are beneficial in reducing heat build-up around solar arrays as the temperature of a solar panel can significantly impact how much electricity the panel produces. As panels get hotter, they produce less power. We estimate the efficiency of a solar panel to be up to 13% higher when installed over a highly reflective membrane compared to a dark membrane with low reflectance. Also, the use of bifacial solar panels over reflective roof membranes can increase the efficiency by 20-35%, as they take advantage of the reflected light.

The benefits of specifying a roof membrane that offers enhanced protection against the effects of UV radiation and high service temperatures, and can maintain high reflectance over a long period of time, makes sense when working with rooftop solar. Therefore, regardless of the type of solar installation, the National Roofing Contractors Association (NRCA) recommends the use of a roof membrane that provides enhanced protection against the effects of UV radiation and high service temperatures – for example, GAF's EverGuard Extreme® TPO – to help ensure that the roof life expectancy will match that of the solar arrays.

Example of a highly reflective roof membrane (installed on the lower roof) that maintains its reflectivity as it ages.


Designers and owners may also want to consider an increased roof membrane thickness to match the service life of the solar arrays. Using wider rolls will minimize the number of seams and reduce the potential for seams to be obscured below solar arrays.

Membrane Attachment

The membrane attachment method should be carefully considered. Adhering the membrane will avoid the normal billowing of mechanically fastened single ply membranes, which could cause ballasted systems to shift and result in localized abrasion of the membrane. The use of a protection or separation sheet installed between ballasted supports and the membrane, extending beyond the contact surface area on all sides, can protect the membrane from abrasion and may be required for warranty or guarantee coverage. The protection sheet should be secured to the roof membrane, not to the bottom of the racking system.

Ballasted systems inadvertently placed directly over fasteners may cut or puncture the membrane as the solar array shifts during strong wind events. Burying fasteners in the roof system will minimize the potential of damage (photo) to the roof membrane, as well as enhance thermal performance of the roof system. This reinforces the use of adhered membranes as well as an adhered top layer of insulation and cover board.

Adhered arrays attached to a mechanically attached or induction welded roof system will billow and flutter with the roof membrane. Over time, this could create additional stress on the solar arrays and their connections, and may compromise the solar and roof system performance. Therefore, an adhered roof membrane will contribute to a roof system lifespan that will better match that of the solar arrays, and help enhance the performance of both. Of course, it's necessary to verify material compatibility, long-term durability and heat aging capabilities of the adhesive to the roof membrane and solar arrays, as well as compliance with local code and uplift resistance requirements.

For attached or penetrating systems (i.e. non-ballasted), mechanically attached membranes could be more acceptable than with ballasted systems. Attached arrays do not move and the array attachment points might act as additional anchors for the membrane.

Cover Boards and Insulation

Roof durability is system dependent so we must look beyond the membrane and consider the entire roof assembly. Rooftops with solar arrays are burdened with more trades and increased foot traffic on the roof, and therefore, are more susceptible to degradation and potential leak sources. An easy starting point is to protect high traffic areas with walkway pads. The addition of a hard cover board such as HD polyiso board will also enhance system protection and extend the life expectancy of the roof.

In addition to increased foot traffic, concentrated loads from ballasted systems can exceed the compressive strength of the roof system's membrane and insulation. Specifying a rigid insulation board with high compressive strength, such as a Grade 3 polyiso, will distribute loads and help prevent crushing that may occur with lower compressive strength materials.

Installation

As the cost to install solar arrays is significant, performing an integrity test of the roof membrane prior to installing the solar overburden is a worthwhile investment of time and resources. Designers must understand that with the installation of rooftop solar, the roof system becomes a permanent platform for the continuous operation, service, and maintenance of the arrays. As many solar designers are not intimately familiar with best roofing practices, it is helpful to specify solar layout requirements for rooftop access that align with not only code requirements (i.e., International Fire Code, (IFC) and National Electric Code (NFPA 70)), but with best practices for roof maintenance and safety of rooftop workers. This can include requirements such as prohibiting solar arrays from crossing expansion joints, and setting solar arrays and rack heights such that field seams, drains, and penetrations are accessible for emergency responders and maintenance workers.

Designers and owners also have the opportunity to specify the type of solar attachment, which includes attached, ballasted, or adhered. Each option will impact decisions for the roof system design so project teams should take a holistic approach to any value engineering discussions regarding the roof and solar arrays.

The importance of the electrical and solar contractors collaborating in concert with roofing contractors and design professionals cannot be overstated. Qualified roof professionals must be integrally involved through the design process and inspection (and repair as needed) of the roof after solar installation. Specifying this as a requirement will ensure the roof contractor is engaged throughout the entire process, leaving your roof in the proper condition to protect what matters most.

Solar Array Attachment

Designers have many choices when it comes to solar array attachment and not all systems are considered equal. The NRCA recommends the use of attached or penetrating systems, mounting systems that are attached through the roof to the structure. Penetrations and flashings must be well detailed and coordinated with the roofing contractor, solar contractor, and electrician. These details are critical to the success of the installation and must be designed to align with the life expectancy of the solar array and roof system.

Attached Solar


Ballasted Solar


Adhered Solar


While ballasted systems are cost effective and easy to install, they can add up to 5 pounds per square foot to the roof. While this loading can be incorporated into the structural design for new construction, it may exceed the capacity of an existing building. Additionally, the concentrated loading of ballasted systems can exceed the compressive strength of the roof insulation. Therefore, the use of a higher compressive strength insulation such as Grade 3 polyiso, should be strongly considered. Better yet, specify a cover board such as HD polyiso for added protection.

Ballasted systems can shift and flutter during high winds and seismic activity. This can result in surface abrasion of the roof membrane which can be "detrimental to satisfactory long-term roof system performance", according to the NRCA. If the project team accepts the risks associated with ballasted systems, a protection or separation sheet should be installed between the ballast supports and the membrane, and should be secured to the roof membrane, not the ballast supports.

Ballasted trays can block or inhibit drainage, which can result in ponding water on the roof membrane. This can undermine the performance and service life of the roof system. Given all the performance challenges with ballasted systems, "NRCA is of the opinion ballasted rack systems do not satisfy the equivalent service life criteria necessary for successful roof system performance throughout the useful life of rooftop-mounted PV systems." However, as ballasted systems are often used, it is important to understand potential issues and use an appropriate design approach with your roof system so the lifespan of the roof can exceed that of the solar arrays.

Another attachment option for solar arrays includes adhered thin-film panels which are adhesively applied directly to the roof membrane. The low profile application makes this system attractive to many designers. Documented compatibility between the roof membrane and the adhesive is critical. Of utmost concern is the potential for adhered solar panels to detach over time as the adhesive ages, and experiences elevated temperatures and repetitive wind uplift forces.

As previously discussed, adhered solar arrays require an adhered roof membrane. And given the increased heat load on the roof system with adhered arrays, a roof membrane with enhanced heat aging properties is even more critical.

Solar Array Layout

The logic behind the layout of solar arrays applies to all attachment options. Solar arrays are usually oriented and laid out for maximum solar energy collection. This includes keeping panels back from walls or equipment that provides shading and away from hot air exhaust that will impact efficiency. Designers should also consider the appropriateness of solar arrays installed in high-wind zones, such as corners and perimeters, to avoid potential uplift failures of the solar arrays or the roof system. Arrays should also be configured in such a way to avoid additional snow accumulation.

The layout of solar arrays should also address access for solar installation, solar array and roof maintenance, and fire safety. Safe access of the solar contractors and electricians during installation, as well as service and maintenance over the service life of the solar arrays, must be accounted for in the design. This may include davits or other tie-off points, perimeter access, and consideration to proximity of overhead power lines. The NRCA Guidelines conveniently summarize the requirements from the International Fire Code (IFC) and National Electric Code (NFPA 70). Generally, they require a 4-foot perimeter around roof edges, hatches and a pathway between the two, as well as a pathway along both centerline axes. They also recommend a 4-foot wide pathway to skylights, ventilation hatches and roof stacks for future serviceability. Best practices for fire safety include 8-foot wide pathways for smoke ventilation between panel arrays, and getting approval from the local fire chief.

Rooftop solar layout guidelines published in NRCA Guidelines.


Roof system maintenance is also an important consideration for solar array layout. It is important to align solar arrays and set rack heights such that there is enough clearance to service the roof membrane, especially drains and penetrations. Providing additional space between the arrays and the roof membrane also increases ventilation and reduces heat build-up, which results in more efficient panels. Generally, the most efficient solar arrays are installed in conjunction with vegetative roofs, as they provide a better climate and temperature for solar panels to function, which improves electricity production. The relatively small payback period and the environmental benefits of combining these two sustainable approaches can balance out the initial investment.

Solar Roof System Design Summary

Clearly, there is a lot to consider when adding solar arrays to the roof. The good news is that as rooftop solar becomes more popular, there are more resources available to designers, owners and contractors to help design, install, and maintain a durable roof system that can match or outlast the service life of solar arrays. In summary, best practices for roof system design when considering solar include:

  • Roof system warranty or guarantee that aligns with or exceeds the life expectancy of the solar array
  • Adhered reflective roof membranes with greater mil thickness that provide enhanced protection against the effects of UV radiation and high service temperatures, such as GAF's EverGuard Extreme® TPO
  • Adhered high-compressive strength cover board directly beneath the roof membrane
  • High compressive strength insulation for ballasted systems (minimum 2 layers staggered and offset)
  • Walk pads for high traffic areas
  • Protection or separation sheet adhered to the membrane for ballasted systems
  • Integrity testing of the roof membrane prior to installing solar overburden
  • Solar layout requirements that align with best practices for roof maintenance
    • Layout solar arrays to maximize solar energy collection while avoiding high wind uplift areas and additional snow accumulation
    • Provide perimeter and maintenance access for roof and solar array maintenance, as well as fire safety and smoke ventilation
    • Set racking systems such that they don't cross roof expansion joints or block drainage
    • Set solar arrays and rack heights such that drains and penetrations are accessible for maintenance
    • Engage the roof contractor to inspect (and repair as needed) the roof membrane after solar array installation

Additional resources available to designers, owners, and contractors alike include the NRCA Guidelines for Roof-Mounted Photovoltaic System Installation, Single Ply Roofing Institute (SPRI) Bulletin on PV Ready Roof Systems, and the Structural Engineering Association (SEAOC) PV manuals for Structural Seismic Requirements and Wind Design.


For more information on roof design considerations when incorporating solar, register for the Continuing Education Center webinar, Commercial Rooftop Solar: Maximizing a Stellar Opportunity, sponsored by GAF and presented by Jennifer Keegan and Thomas J. Taylor.

About the Author

Jennifer Keegan is the Director of Building & Roofing Science for GAF, focusing on overall roof system design and performance. Jennifer has over 20 years of experience as a building enclosure consultant specializing in assessment, design and remediation of building enclosure systems. Jennifer provides technical leadership within the industry as the Chair of the ASTM D08.22 Roofing and Waterproofing Subcommittee; and as an advocate for women within the industry as the educational chair for National Women in Roofing and a board member of Women in Construction.

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Building Science

Thermal Bridging Through Roof Fasteners: Why the Industry Should Take Note

What is going on here?No, this roof does not have measles, it has a problem with thermal bridging through the roof fasteners holding its components in place, and this problem is not one to be ignored.As building construction evolves, you'd think these tiny breaches through the insulating layers of the assembly, known as point thermal bridges, would matter less and less. But, as it happens, the reverse is true! The tighter and better-insulated a building, the bigger the difference all of the weak points, in its thermal enclosure, make. A range of codes and standards are beginning to address this problem, though it's important to note that there is often a time lag between development of codes and their widespread adoption.What Is the Industry Doing About It?Long in the business of supporting high-performance building enclosures, Phius (Passive House Institute US) provides a Fastener Correction Calculator along with a way to calculate the effect of linear thermal bridges (think shelf angles, lintels, and so on). By contrast, the 2021 International Energy Conservation Code also addresses thermal bridging, but only considers framing materials to be thermal bridges, and actually pointedly ignores the effects of point loads like fasteners in its definition of continuous insulation: "insulation material that is continuous across all structural members without thermal bridges other than fasteners and service openings" (Section C202). Likewise, The National Energy Code of Canada for Buildings: 2020 addresses thermal bridging of a number of building components, but also explicitly excludes fasteners: "in calculating the overall thermal transmittance of assemblies…fasteners need not be taken into account" (Section 3.1.1.7.3). Admittedly, point thermal bridges are often excluded because it is challenging to assess them with simple simulation tools.Despite this, researchers have had a hunch for decades that thermal bridging through the multitude of fasteners often used in roofs is in fact significant enough to warrant study. Investigators at the National Bureau of Standards, Oak Ridge National Laboratory, the National Research Council Canada, and consulting firms Morrison Hershfield and Simpson Gumpertz & Heger (SGH), have conducted laboratory and computer simulation studies to analyze the effects of point thermal bridges.Why Pay Attention Now?The problem has been made worse in recent years because changes in wind speeds, design wind pressures, and roof zones as dictated by ASCE 7-16 and 7-22 (see blogs by Jim Kirby and Kristin Westover for more insight), mean that fastener patterns are becoming denser in many cases. This means that there is more metal on average, per square foot of roof, than ever before. More metal means that more heat escapes the building in winter and enters the building in summer. By making our buildings more robust against wind uplift to meet updated standards, we are in effect making them less robust against the negative effects of hot and cold weather conditions.So, how bad is this problem, and what's a roof designer to do about it? A team of researchers at SGH, Virginia Tech, and GAF set out to determine the answer, first by simplifying the problem. Our plan was to develop computer simulations to accurately anticipate the thermal bridging effects of fasteners based on their characteristics and the characteristics of the roof assemblies in which they are used. In other words, we broke the problem down into parts, so we could know how each part affects the problem as a whole. We also wanted to carefully check the assumptions underlying our computer simulation and ensure that our results matched up with what we were finding in the lab. The full paper describing our work was delivered at the 2023 IIBEC Convention and Trade Show, but here are the high points, starting with how we set up the study.First, we began with a simple 4" polyisocyanurate board (ISO), and called it Case A-I.Next, we added a high-density polyisocyanurate cover board (HD ISO), and called that Case A-II.Third, we added galvanized steel deck to the 4" polyiso, and called that Case A-III.Finally, we created the whole sandwich: HD ISO and ISO over steel deck, which was Case A-IV.Note that we did not include a roof membrane, substrate board, air barrier, or vapor retarder in these assemblies, partly to keep it simple, and partly because these components don't typically add much insulation value to a roof assembly.The cases can be considered base cases, as they do not yet contain a fastener. We needed to simulate and physically test these, so we could understand the effect that fasteners have when added to them.We also ran a set of samples, B-I through B-IV, that corresponded with cases A-I through A-IV above, but had one #12 fastener, 6" long, in the center of the 2' x 2' assembly, with a 3" diameter insulation plate. These are depicted below. The fastener penetrated the ISO and steel deck, but not the HD ISO.One visualization of the computer simulation is shown here, for Case B-IV. The stripes of color, or isotherms, show the vulnerability of the assembly at the location of the fastener.What did we find? The results might surprise you.First, it's no surprise that the fastener reduced the R-value of the 2' x 2' sample of ISO alone by 4.2% in the physical sample, and 3.4% in the computer simulation (Case B-I compared to Case A-I).When the HD ISO was added (Cases II), R-value fell by 2.2% and 2.7% for the physical experiment and computer simulation, respectively, when the fastener was added. In other words, adding the fastener still caused a drop in R-value, but that drop was considerably less than when no cover board was used. This proved what we suspected, that the HD ISO had an important protective effect against the thermal bridging caused by the fastener.Next, we found that the steel deck made a big difference as well. In the physical experiment, the air contained in the flutes of the steel deck added to the R-value of the assembly, while the computer simulation did not account for this effect. That's an item that needs to be addressed in the next phase of research. Despite this anomaly, both approaches showed the same thing: steel deck acts like a radiator, exacerbating the effect of the fastener. In the assemblies with just ISO and steel deck (Cases III), adding a fastener resulted in an R-value drop of 11.0% for the physical experiment and 4.6% for the computer simulation compared to the assembly with no fastener.Finally, the assemblies with all the components (HD ISO, ISO and steel deck, a.k.a. Cases IV) showed again that the HD ISO insulated the fastener and reduced its negative impact on the R-value of the overall assembly. The physical experiment had a 6.1% drop (down from 11% with no cover board!) and the computer simulation a 4.2% drop (down from 4.6% with no cover board) in R-value when the fastener was added.What Does This Study Tell Us?The morals of the study just described are these:Roof fasteners have a measurable impact on the R-value of roof insulation.High-density polyisocyanurate cover boards go a long way toward minimizing the thermal impacts of roof fasteners.Steel deck, due to its high conductivity, acts as a radiator, amplifying the thermal bridging effect of fasteners.What Should We Do About It?As for figuring out what to do about it, this study and others first need to be extended to the real world, and that means making assumptions about parameters like the siting of the building, the roof fastener densities required, and the roof assembly type.Several groups have made this leap from looking at point thermal bridges to what they mean for a roof's overall performance. The following example was explored in a paper by Taylor, Willits, Hartwig and Kirby, presented at the RCI, Inc. Building Envelope Technology Symposium in 2018. In that paper, the authors extended computer simulation results from a 2015 paper by Olson, Saldanha, and Hsu to a set of actual roofing scenarios. They found that the installation method has a big impact on the in-service R-value of the roof.They assumed a 15,000-square-foot roof, fastener patterns and densities based on a wind uplift requirement of 120 pounds per square foot, and a design R-value of R-30. In this example, a traditional mechanically attached roof had an in-service R-value of only R-25, which is a 17% loss compared to the design R-value.An induction-welded roof was a slight improvement over the mechanically attached assembly, with an in-service value of only R-26.5 (a 12% loss compared to the design R-value).Adhering instead of fastening the top layer of polyiso resulted in an in-service R-value of R-28.7 (a 4% loss compared to the design R-value).Finally, in their study, an HD polyiso board was used as a mechanically fastened substrate board on top of the steel deck, allowing both layers of continuous polyiso insulation and the roof membrane to be adhered. Doing so resulted in an in-service R-value of R-29.5, representing only a 1.5% loss compared to the design R-value.To operationalize these findings in your own roofing design projects, consider the following approaches:Consider eliminating roof fasteners altogether, or burying them beneath one or more layers of insulation. Multiple studies have shown that placing fastener heads and plates beneath a cover board, or, better yet, beneath one or two layers of staggered insulation, such as GAF's EnergyGuard™ Polyiso Insulation, can dampen the thermal bridging effects of fasteners. Adhering all or some of the layers of a roof assembly minimizes unwanted thermal outcomes.Consider using an insulating cover board, such as GAF's EnergyGuard™ HD or EnergyGuard™ HD Plus Polyiso cover board. Installing an adhered cover board in general is good roofing practice for a host of reasons: they provide enhanced longevity and system performance by protecting roof membranes and insulation from hail damage; they allow for enhanced wind uplift and improved aesthetics; and they offer additional R-value and mitigate thermal bridging as shown in our recent study.Consider using an induction-welded system that minimizes the number of total roof fasteners by dictating an even spacing of insulation fasteners. The special plates of these fasteners are then welded to the underside of the roof membrane using an induction heat tool. This process eliminates the need for additional membrane fasteners.Consider beefing up the R-value of the roof insulation. If fasteners diminish the actual thermal performance of roof insulation, building owners are not getting the benefit of the design R-value. Extra insulation beyond the code minimum can be specified to make up the difference.Where Do We Go From Here?Some work remains to be done before we have a computer simulation that more closely aligns with physical experiments on identical assemblies. But, the two methods in our recent study aligned within a range of 0.8 to 6.7%, which indicates that we are making progress. With ever-better modeling methods, designers should soon be able to predict the impact of fasteners rather than ignoring it and hoping for the best.Once we, as a roofing industry, have these detailed computer simulation tools in place, we can include the findings from these tools in codes and standards. These can be used by those who don't have the time or resources to model roof assemblies using a lab or sophisticated modeling software. With easy-to-use resources quantifying thermal bridging through roof fasteners, roof designers will no longer be putting building owners at risk of wasting energy, or, even worse, of experiencing condensation problems due to under-insulated roof assemblies. Designers will have a much better picture of exactly what the building owner is getting when they specify a roof that includes fasteners, and which of the measures detailed above they might take into consideration to avoid any negative consequences.This research discussed in this blog was conducted with a grant from the RCI-IIBEC Foundation and was presented at IIBEC's 2023 Annual Trade Show and Convention in Houston on March 6. Contact IIBEC at https://iibec.org/ or GAF at BuildingScience@GAF.com for more information.

By Authors Elizabeth Grant

November 17, 2023

GAF Building and Roofing Science Team
Building Science

Developing Best Practice Solutions for GAF and Siplast Customers

With any roofing project, there are a number of factors to consider when choosing the right design: sustainability profile, potential risks, overall performance, and more. Our Building and Roofing Science (BRS) team specializes in working with industry professionals to help them enhance their roof designs across all of these areas. Leveraging their building enclosure expertise, our BRS team serves as thought leaders and collaborators, helping design professionals deliver better solutions for their customers."We're a consultant's consultant. Basically, we're a sounding board for them," explains Jennifer Keegan, Director of Building and Roofing Science. Rather than solely providing product specifications and tactical support, the BRS team partners with consultants, specifiers, and architects to provide guidance on designing high-performing roofs that don't just meet code, but evolve their practices and thinking. For example, this might include understanding the science behind properly placed air and vapor retarders.As experts in the field, our BRS team members frequently attend conferences to share their expertise and findings. As Jennifer explains, "Our biggest goal is to help designers make an informed decision." Those decisions might be in a number of areas, including the building science behind roof attachment options, proper placement of air and vapor retarders, and how a roof can contribute to energy efficiency goals.Expanding the BRS TeamOur BRS team is accessible nationwide to look at the overall science of roof assembly and all of the components and best practices that make up a high-performance, low-risk, and energy-efficient roof. Our regional experts are positioned strategically to better serve our customers and the industry as a whole. We have the capacity to work with partners across the country on a more personalized level, providing guidance on roof assembly, membrane type, attachment method, or complicated roof details including consideration of the roof to wall interface.Partnering with the Design Services TeamIn addition to our newly expanded BRS team, GAF also offers support through its Design Services team. This group helps with traditional applications, installations, and system approvals. GAF's Design Services team is a great resource to answer any product questions, help you ensure your project meets applicable code requirements, assess compatibility of products, outline specifications, and assist with wind calculations. By serving as the front line in partnership with our BRS team, the Design Services team can help guide the design community through any phase of a project.GAF's Building and Roofing Science team is the next step for some of those trickier building projects, and can take into consideration air, vapor, and thermal requirements that a designer might be considering for their roof assembly. Through a collaborative process, our BRS team seeks to inspire project teams, as Jennifer explains, "to do it the best way possible."Engaging with the TeamsGAF has the support you need for any of your design and roofing science needs. To request support from the GAF Design Services team, you can email designservices@gaf.com. For additional support from our Building and Roofing Science team regarding specialty installations or how a building can be supported by enhanced roof design, contact us at buildingscience@gaf.com.Our Building and Roofing Science team is always happy to support you as you work through complex jobs. You can also sign up to join their office hours here.

By Authors GAF Roof Views

May 08, 2023

Edge metal
Building Science

Edge Metal Design Wall Zones 4 and 5

Keeping water out of a building is undoubtedly the primary function of a roof system. But one could argue that ensuring a building's roof stays in place during high-wind events is equally important. Let's face it, without a roof, it's hard to keep water out! This blog takes a look at one of the subsets of wind design of roof systems: Wall Zones 4 and 5 and their relationship with roof perimeters.IntroductionArchitects, specifiers, and roof system designers are generally focused on the wind-uplift capacity of the roof system itself. Wind resistance of perimeter edges and parapets might not be front of mind, especially given the myriad roof-system Approval Listings that can be found through DORA, FM, and UL. However, rooftop perimeters and corner areas are most vulnerable to high wind, and perimeter edge metal and copings are part of the first line of defense. Codes now include wind-design and system testing for edge metal and copings. FM also just recently (late 2021) updated RoofNav's Wind Rating Calculator to include fascia, copings, and gutters.Edge metal and copingsThe term 'edge metal' encompasses three foundational shapes that are used at a roof's perimeter: L-shaped metal, gravel stop metal, and copings for parapets. The figures below show generic shapes; ones that are often contractor-fabricated. Additionally, there are many manufacturers that provide edge metal. Some of the manufacturer-fabricated shapes are similar to those shown below. However, some are a bit more distinct and some are extruded to achieve more unique shapes.Graphic adapted from National Roofing Contractors AssociationSome examples of GAF's metal details are shown here:Steel and aluminum are common materials used for edge metal shapes and copings. Some are galvanized; some are painted. Commonly used thicknesses range from 20 gauge to 24 gauge for steel and 0.032" to 0.040" for aluminum. The continuous cleat is typically one gauge thicker than the edge metal and coping.Why is wind design of edge metal important?The roofing industry has been investigating high-wind events, primarily through a group called the Roofing Industry Committee on Weather Issues (RICOWI). RICOWI was established in 1990 and has published numerous reports based on post-wind-event investigations of damage caused by hurricanes. RICOWI's most recent report, released November 19, 2019, covers their investigation of the damage caused by Hurricane Michael. RICOWI has published five reports covering their investigations of 6 hurricanes since 2004.One of the most consistent conclusions throughout the series of 5 reports of post-event investigations is that the majority of localized roof damage and roof system failures due to high winds commonly begin at perimeters and corners. This is not surprising as the highest wind loads are at rooftop perimeters and corners. This blog about wind design and ASCE-16, among other topics, discusses the process and factors used to determine wind loads, and it provides additional information about roof zone layout. Localized roof damage and roof system failures due to high winds commonly begin at perimeters and corners. Not recognizing the importance of edge metal design relative to the overall wind performance of a roof system can result in edge metal installations that may not have the appropriate wind-resistance capacity. This could possibly result in localized damage and/or system failures, even when the roof system (i.e., deck, insulation, membrane) is appropriately designed for design wind loads.The following information is intended to supplement the wind design concepts that were discussed in GAF's earlier blog about wind design and ASCE 7-16.Roof and Wall ZonesWind design of metal edges and copings includes an upward and an outward component, unlike the primary roof system which includes an upward component only. (The Edge Metal Testing section of this blog has more information on that topic). ASCE 7 calls the outward pressures acting on metal edges and copings Wall Zones 4 and 5. Wall Zone 4 correlates and is aligned with Roof Zone 2 (the perimeter zones), and Wall Zone 5 is aligned with Roof Zone 3 (the corner zones). The figure shows one example of a building's roof and wall zones. Case studies from this blog provide more specific information related to the figure below.What do the codes say?The International Building Code (IBC) includes requirements for determining the wind-load capacity for metal edges and copings. This requirement has been included since the 2003 version of the IBC. In other words, edge metal and copings should have wind-resistance capacities greater than the design wind pressures. This concept is just like wind design for the primary roof system—the capacity of the system needs to be greater than the anticipated loads.Chapter 15, Section 1504.5 from the 2015 IBC includes requirements for determining the capacity of metal edges and copings."1504.5 Edge securement for low-slope roofs. Low-slope built-up, modified bitumen and single-ply roof system metal edge securement, except gutters, shall be designed and installed for wind loads in accordance with Chapter 16 and tested for resistance in accordance with Test Methods RE-1, RE-2 and RE-3 of ANSI/SPRI ES-1, except Vu1t wind speed shall be determined from Figure 1609A, 1609B, or 1609C as applicable."Chapter 16 of the IBC indirectly includes requirements for determining the wind loads acting on metal edges and copings. In Section 1609.1 Applications, the IBC states "Buildings, structures and parts thereof shall be designed to withstand the minimum wind loads…" The "parts thereof" encompasses metal edges and copings. The requirement in Chapter 15 to design and install metal edges and copings means the outward pressures for Wall Zones 4 and 5 need to be determined.It's worth noting that the scope of the ANSI/SPRI ES-1 test method does not include gutters, which is why gutters are specifically excluded in the code language through 2018. However, SPRI, in 2016, published ANSI/SPRI GT-1, Test Standard for Gutters, which was first included in model codes in the 2021 IBC.Edge metal testingDetermining the design wind pressures (in pounds per square foot) for Wall Zones 4 and 5 is generally the responsibility of the design professional, such as the architect or structural engineer. On the other hand, determining the capacity of metal edges and copings is generally the responsibility of the manufacturer, which may be a manufacturing company or a roofing contractor that fabricates their own metal edges, coping, and clips and cleats.The IBC specifically lists ANSI SPRI ES-1, Test Standard for Edge Systems Used with Low Slope Roofing, as the test method to be used to determine capacity for metal edges and copings. ES-1 includes three (3) test methods (RE-1, RE-2, RE-3), each for a different edge condition.The RE-1 test method is for 'dependently terminated roof membrane systems'. Essentially, a mechanically attached or ballasted membrane is considered to be dependently terminated if a "peel stop" or row of fasteners is not included within 12" from the roof edge. Without a peel stop or a row of fasteners close to the edge of the roof, the edge metal is acting as the mechanical attachment of the perimeter of the membrane. (The RE-1 figure below is rotated clockwise 115 degrees to show the as-tested configuration of the metal edge. ES-1 presumes a ballasted or mechanically attached membrane will flutter and apply load to the metal edge at 25 degrees. The rotated configuration accommodates a hanging load.)The RE-2 test method is for essentially all metal edge types as long as the "horizontal component" is 4" wide or less.The RE-3 test method is for copings, and RE-3 includes two tests. One test includes an upward load and a 'face' load; the second test includes an upward load and the 'back leg' load.The wind-resistance capacity of metal edges and copings is provided in "pounds per square foot" (psf). This is appropriate because the design wind pressures are also in PSF values which makes the comparison of design wind pressures to wind-resistance capacity simple.Where to find Approval Listings for edge metalSimilar to approval listings for roof systems, there are approval listings for metal edges and copings. Approval Listings are found on FM's RoofNav and UL's Product IQ. An account (free) is required for both. Additionally, NRCA has Approval Listings for contractor-fabricated metal edges and copings which are housed on UL's Product IQ and Intertek's Directory of Building Products.ULKnowing UL's Category Control Number is key to navigating UL's Product IQ. . For metal edges and coping, UL's Category Control Number is "TGJZ". After logging in, performing a search using "TGJZ" provides a list of the manufacturers that have Approval Listings with UL. Clicking on GAF's Approval Listings allows users to easy find rated Roof-edge Systems, Metal, for Use with Low-slope Roofing Systems.Within UL's TGJZ category, GAF has 16 metal-edge products rated using the RE-2 test method and 8 coping products rated using the RE-3 test method. For example (as shown in item 3 in the screen capture above), GAF's M-Weld Gravel Stop MB Fascia B made with aluminum is rated "190 psf". That means this product can be used when the design wind pressures, which include a safety factor, for Wall Zones 4 and 5 are less than or equal to 190 psf.FM's RoofNavWithin RoofNav, Approval Listings for metal edges and copings can be found under "Product Search" using the "Flashing" category. Most likely, users of RoofNav are familiar with the "Assembly Search" function which is regularly used to locate roof systems based on their wind-uplift ratings.The search can be further refined within "Subcategory" by selecting Expansion Joint, Gutter, or Perimeter Flashing.Currently, GAF has 59 Approval Listings in RoofNav: 12 for Coping, 41 for Fascia, and 6 for Gutter products. A screen capture from RoofNav shows GAF's first 20 products.Looking closely at the Listing, the EverGuard EZ Fascia AR – Steel provides detailed information about the product itself and the installation requirements. As shown below, the listing includes multiple Ratings (i.e., wind-uplift capacity) based on material type and thickness, and face height.While the Listing is for a steel fascia, an aluminum fascia is also shown in the detailed information. It's important to note that the chart with the "steel" listing's detailed information is the same chart that is available for EverGuard EZ Fascia AR – Aluminum, as well. Therefore, it's prudent for designers and specifiers to provide appropriate information in the specification to avoid mis-communiction about intended product use.Take note of the material and gauge of the "retainer" (i.e., the continuous cleat). The continuous cleat is required to be 0.50 aluminum, regardless of fascia material type for this Listing. Because the strength of the cleat is a significant factor to the overall wind-uplift capacity of the metal edge (or coping), increasing the thickness of the cleat proves to be an effective method to increase performance.FM RoofNav and Edge SecurementFM announced on its website on October 28, 2021 that "The Wind Ratings Calculator has been updated to return separate flashing ratings for roofs." The red-highlighted area shows the required capacity for Fascia, Coping, and Gutter products.Comparison of the Minimum Wind Uplift Approval Ratings Needed (1-75, 1-90) to the Perimeter and Corner Ratings of the EverGuard EZ Fascia shows that each product type provides the required capacity, and in most cases the required capacity greatly exceeds the required rating.Load PathThe 3 test methods included in ANSI/SPRI ES-1 standard determine the wind-resistance capacity of edge metal attached to a substrate. In other words, the measured capacity (Rating) is of the metal edge or coping attached to the wood blocking; the tests do not measure the capacity of the attachment of the wood blocking to any substrate. The National Roofing Contractors provide information on this topic. The NRCA Roofing Manual: Membrane Roof Systems—2019, on page 289 states:"Wood Nailers and Blocking: Many of the construction details illustrated in this manual depict wood nailers and blocking at roof edges and other points of roof termination. Wood nailers must be adequately fastened to the substrate below to resist uplift loads. This especially is true at parapet walls/copings and roof edges where edge-metal shapes are fastened to wood blocking.Among other advantages, the nailers provide protection for the edges of rigid board insulation and provide a substrate for anchoring flashing materials. Wood nailers should be a minimum of 2 x 6 nominal-dimension lumber. To provide an adequate base, nailers should be securely attached to a roof deck, wall and/or structural framing. In the design of specific details for a project, a designer should describe and clearly indicate the manner in which wood nailers and/or blocking should be incorporated into construction details. A designer should specify the means of attachment, as well as the fastening schedule for all wood nailers and blocking."To that end, FM Global Property Loss Prevention Data Sheet 1-49, Perimeter Flashings, provides a number of recommendations for anchoring wood blocking to various types of walls and structural framing. One example of a roof/wall intersection shows the bottom nailer bolted to the bar joists to ensure an adequate load path.In SummaryArchitects, specifiers, and roof system designers are required by code (always check specific local requirements) to determine wind loads not only for the primary roofing system, but for the metal edges and copings as well. Manufacturers and fabricators are responsible for determining the wind-uplift capacity of their metal edge and coping products, as well as their primary roofing systems.Given the relatively new requirements in the IBC for edge securement, designers, consultants, and specifiers should become familiar with both UL's and FM's approval listings for metal edges and copings. Manufacturers of metal edge and coping products are available to assist designers with selection of edge securement.

By Authors James R Kirby

April 24, 2023

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