Low-slope roofs continue to present challenges in windstorms. Despite the development of new standards for materials and installation and continual code improvements, there has been little improvement in overall performance and little reduction in the frequency of damage to these roof systems. This assessment focuses on the role played by edge metal systems in the larger performance of low-slope roof covers.
Edge metal systems play a crucial role in terminating roof and wall covers for buildings with a low-slope roof. Its primary function is to preserve the building’s integrity against wind and water infiltration. These systems are susceptible to failure during high-wind events and lead to a cascade of damage to the roof system, the overall building, and its contents. In the context of low-slope roofs, edge metal systems are categorized into flashing and coping, with flashing terminating the roofing system at a 90-degree angle where the wall and roof converge, whereas coping is employed when the building features a parapet. Flashing systems are composed of an inner metal cleat mechanically fastened to the building’s wall, an outer metal fascia component secured to the cleat, and an upper flange that connects to a wood nailer. The wood nailer (solid dimensional lumber), bolted to the wall, serves as a substrate for the perimeter edge and coping systems.
Field investigations by the Roofing Industry Committee on Weather Issues Inc. (RICOWI) from the devastating 2004 and 2005 hurricane seasons through Hurricane Michael in 2018 documented performance issues and several different damage modes associated with flashing failures in sub-design wind conditions.1,2,3,4 The Insurance Institute for Business & Home Safety (IBHS) explored commercial low-slope roofing performance following Hurricane Ian (2022) using remote sensing imagery and found a damage frequency of nearly 50 percent for membrane and built-up roofs. For those roofs with identifiable damage, 71 percent had visible damage to flashing and/or coping.5 The RICOWI post-Hurricane Ian investigation also found similar damage modes to flashing and coping that had been documented extensively in previous hurricanes.6
Even before the 2004 hurricane season, the performance and losses associated with low-slope roofing served as the catalyst to develop a new standard for edge metal systems to improve their performance in windstorms.7 In 1998, the Single Ply Roofing Industry (SPRI) used the American National Standards Institute (ANSI) process to develop the ES-1 test to standardize resistance testing for roof edge metal systems. The standard first entered model codes in 2003 through the International Building Code (IBC) and subsequently the Florida Building Code (FBC) in 2004 and has been referenced ever since. In 2011, FM (formerly FM Global) collaborated with SPRI to align their test method, FM 4435, with the existing SPRI standard to create a combined document ANSI/SPRI/FM 4435 ES-1 (ES-1).
In investigating building performance following Hurricane Ian, IBHS explored the possible impact of this standard on edge metal performance through its inclusion in the FBC.8 The results, shown in Table 1, indicate there has been a clear improvement in both the broader roof cover performance and the performance of flashing and coping. The recent results following Hurricane Ian indicate the benefits of implementing this standard. However, the frequency of edge metal damage when cover damage is present remains near or above
50 percent. This includes structures built under modern FBC editions that incorporate the updated ES-1 standard.9 These damage frequencies suggest that this issue still represents a large source of loss. The damage frequencies observed over the past two decades also occurred in sub-design wind conditions except in specific instances from Hurricane Charley (2004) and Hurricane
Michael (2018).
Given the damage rates observed, RICOWI and IBHS explored possible reasons why damage rates—while lower for modern FBC construction (2004-present)—are still relatively high in sub-design conditions. Through performance observations made by
both IBHS and RICOWI, the following themes and questions were identified as possible areas that could explain the current performance:
- Are the wind loads included in ASCE 7-22 adequate for the real world conditions edge metal systems are subjected to in severe windstorms?
- Are the ES-1 provisions properly accounted for in pertinent design and design documents?
- Are the code and the underlying standards being properly inspected and enforced uniformly?
- As with nearly all building components and assemblies, how prevalent is improper installation workmanship?
- Are there damage modes that have become more evident as broader progress has been made on low-slope roofing, and what other considerations could affect performance?
In this white paper, the authors address the questions above individually, aiming to provide possible explanations for the observed performance and pathways forward to continue fostering progress in addressing low-slope roof performance and the associated edge metal performance.
Are the wind loads prescribed adequate for edge metal systems on low-slope roofs?
IBHS developed a full-scale experimental testing program to explore the potential under-representation of wind loads on flashing as currently specified in ASCE 7-22.
IBHS constructed a 112-m2 (1,200-sf) light commercial building. The roof cover system was composed of a 1-mm (0.04-in.) thick polyvinyl chloride (PVC) membrane that covered a 12.7-mm (0.5-in.) thick gypsum cover board over 25.4-mm (1-in.) polyisocyanurate (Polyiso) insulation board with mitered corners for the flashing system for stability. The cover board and Polyiso board were mechanically fastened down by six fasteners per board. The PVC membrane was held down with 60.3-mm (2.375-in.) round cleat plates with a spacing of 152.4 mm (6 in.) on the center. The membrane was heat welded per the manufacturer’s instructions, giving it a seam-to-seam sheet width of 1.5 m (5 ft). Figure 1 displays the test specimen in the IBHS test chamber. The specimen was tested across different wind directions using 10-degree increments at 90, 103, and 147 km/h (56, 64, and 91 mph), peak wind speeds, and subsequent loading conditions. Throughout construction, pressure transducers were installed to measure the wind pressure acting on the roof flange, wall flange, and hem of the flashing system at 18 building locations. At each of these 18 locations, a pressure sensor located on the wall approximately 0.3 m (1 ft) down from the leading edge and a pressure sensor located on the roof approximately 0.9 m (3 ft) away from the leading edge was installed to compare the loads on the flashing to the loads experienced by the wall and roof.
The full-scale testing provided the following results.10
- Wind load measurements were above ASCE7-22 design loads for the wall flange, hem, and roof corner. The measured pressures and calculated wind loads exceeded those prescribed in ASCE 7-22 for the roof flange on
70 percent of wind directions with
100 percent exceedance for the wall flange and hem of the flashing system. - The capping of loads currently in ASCE 7-22 for flashing appears insufficient.
- Currently, the ES-1 standard and its underlying test requirements do not account for the multiple damage modes, specifically the physical uplift on the flashing, as it is pulled both outward and upwards by the flow regime. The ES-1 standard and its underlying testing requirements only account for the forces pulling flashing elements outward away from the wall.
These key recommendations came from the testing program:
- Treat edge/flashing details separate from the main building load calculations. Flashing functions as a unique component, but it has been proven to be an initial point of failure for low-slope roofing systems.
- Allow loads to follow their exponential increase observed in experimental testing rather than capping load provisions.
Design, installation, and enforcement
The real performance of low-slope roofing and its edge metal details begins with the system’s design and how it is installed on the building itself. The concern is that edge metal details are not adequately tested according to the ES-1 standard, especially when unique design requirements are presented.
Additionally, field installations must be completed in accordance with the exact design as it was tested. Any changes in the installation—such as changes in the gauge of the fascia or metal cleat, type of fasteners, fastener spacing, substrate, etc.—will affect the performance. Once the field installation deviates from the design, the performance expectations are unknown and differ from the originally designed, tested, and approved system.
As with all codes and standards, enforcing testing standards and subsequent provisions is key to ensuring proper installation and performance in the field. The lack of uniform enforcement of code provisions has been extensively documented as a driver of poor building performance in windstorms across all types of structures. It is included as a key metric by IBHS within its “Rating the States” code evaluation program.11 When exploring building performance, the uniform enforcement of code provisions designed for damage mitigation is often a topic for inclusion. This is especially true when considering the performance of low-slope roofing and, specifically, edge metal details as an initiation mechanism for low-slope roof damage. The ES-1 standard has been included in both the IBC and the FBC for 20 years to help improve the performance of these roof systems and mitigate one of the potential points of damage initiation.
This context considers the potential challenges in enforcing provisions related to edge metal systems. By referencing manufacturer specifications during the permitting process, code officials can efficiently evaluate building designs and verify that edge metal systems comply with product approvals.
However, ensuring the designed and permitted elements are accounted for and met during installation is a greater challenge. This was noted by Graham (2009) and the National Roofing Contractors Association (NRCA) in 2009 when considering difficulties in
low-slope roofing edge details.12 Physical inspections during installation are subject to resource limitations and other logistical issues, including construction project timelines.
The observations and hypotheses developed here are based on qualitative ground-based inspections of specific structures and their damage and a quantitative aerial damage study from Hurricane Ian.13 The damage rates and identified reduction in damage are specifically from Florida, which has one of the most stringent wind mitigation code systems in the United States. Similar analyses should be conducted in areas with a less robust code enforcement system to determine the role that code enforcement plays on both low-slope roof performance and edge metal performance on those systems. Such analyses could help quantify the impact of code enforcement on edge metal system performance.
The understanding and enforcement of ES-1 is perhaps inconsistent. Roofing contractors have acknowledged their lack of familiarity with the code-referenced standard and the need for effective testing of designs; especially variants developed for specific building designs. However, one could argue that contractors would be more familiar or accustomed to the standard and its test methods if it were more uniformly enforced by code jurisdictions where the contractors perform work. It is unclear at this point where the breakdown occurs. Each
three-year cycle of building code updates is communicated to jurisdictions so they are aware of new requirements. ES-1 was first adopted as a code-referenced standard in the 2003 IBC more than 20 years ago. However, even with this long history, a lack of understanding and enforcement of this standard has been documented within the construction industry.
Additional damage modes and contributing factors
Edge metal failures are also exacerbated by the absence of proper waterproofing details that can compromise the integrity of the substrate that the edge metal is attached to, typically moisture-sensitive wood. Exposure to cyclical wetting/drying over the service life of a building can be associated with a significant reduction in the wind resistance of the mechanical attachment of the edge metal components. Specifically, the fasteners used to attach continuous cleats on the exterior face and/or those used to attach the interior face of the coping can become weak in the presence of wood decay or rot.
It is important that coping systems are designed with a safety factor of 2.0 or greater because compromising a single fastener will increase the load to the adjacent fasteners by 50 percent. This simple example shows that a reasonable safety factor is important to edge metal assemblies’ long-term durability and function. Contractors need to understand the importance of proper moisture protection of the wood components below the edge metal to avoid long-term compromise of the substrate. On a related note, the fasteners used to attach edge metal components must be properly driven into and placed correctly on the wood substrate and not located too close to the edge of a board or at a gap/joint in between boards, which can drastically reduce the withdrawal capacity of the fastener.
Also, the wood nailer must be in good condition, rot-free, and properly secured to the wall. If the nailer fails, it creates a cascade as all components above the nailer fail, which may lead to partial or complete loss of roof cover. An example of this type of failure is shown in Figure 2.
Pathways forward to continue driving ahead performance improvements
The performance of low-slope roofing and its associated edge metal details following Hurricane Ian provided both optimism and cause for concern. The performance of low-slope roofs built under the modern FBC and under the requirements of the ES-1 testing standard demonstrates an improvement relative to older construction. However, the frequency of damage, even on newer structures built under the more stringent environment, still approached 40 percent during Hurricane Ian. The result suggests the performance of low-slope roofing continues to be a considerable cause of damage and loss. Existing programs and processes that include and require additional scrutiny, onsite inspections, and compliance anecdotally have seen fewer losses than what was observed following Hurricane Ian (2022).14, 15, 16
The commentary provided here identifies areas where gaps may exist and contribute to the picture of loss seen today. It also allows for the development of pathways to continue the performance improvement of low-slope roofing and its associated edge metal. The following are areas that could provide paths towards improving performance:
- Ensure wind loads on edge metal systems are properly captured and accounted for in design and test standards. As experimental testing on wind loads advances, ASCE7 and ES-1 should adapt together.
- ES-1 is a product evaluation standard. All facilities, including contractors and fabrication facilities, that produce ES-1 designs are also required to be part of the overall product evaluation program for the system to have its maximum impact.
- Focused post-event damage investigations can identify the common failure modes in the field by providing information to guide and/or validate experimental testing and better understand the influence of installation practices and enforcement. In addition, they can quantify damage to low-slope cover systems that occurred without edge metal damage initiation.
- As with any building system, it is always important to couple design specifications with physical inspections by installers and code officials.
- Experimental testing could be designed to understand performance sensitivity to installation errors. The testing could also serve to determine the adequacy of safety factors typically used in design. For example, fastener spacing could be varied to explore when a failure threshold is reached, helping identify when installation errors become an important factor in poor performance.
- As the framework for tornado-based design becomes accepted in areas of the United States away from the
hurricane-prone coast, there will be a greater emphasis on edge metal detail. Thus, education, outreach, and enforcement will become more important to ensure edge metal systems are properly tested and assembled. - While ES-1 is currently referenced in the IBC, it is not in the International Residential Code (IRC). Residential structures are increasingly utilizing different roof types, including typical low-slope systems. The inclusion of the ES-1 standard into the IRC should be considered.
The Roofing Industry Committee on Weather Issues, Inc. (RICOWI) was established in 1990 as a non-profit organization to identify and address important technical issues related to the cause of wind damage, which include:
- Dynamic testing of roof systems.
- Importance of sample size for tests.
- Role of wind tunnels and air retarders.
- Need for acceptable procedures for ballasted systems.
- Field data and response team reports.
- General lack of communication within the roofing industry as to what the problems are, what is being done and should be done to alleviate them, and how effectively information is transferred within the roofing industry and to others in the building community.
The Insurance Institute for Business & Home Safety (IBHS) is an independent, 501(c)(3) nonprofit scientific research and communications organization supported by property insurers, reinsurers, and affiliated companies. IBHS’s building safety research leads to real-world solutions for home and business
owners, helping to create even more resilient communities.
IBHS delivers top-tier science and translates it into action to prevent avoidable suffering, strengthen homes and businesses, inform the insurance industry, and support thriving communities.
Notes
1 RICOWI, Inc., 2006: “Hurricanes Charley and Ivan Wind Investigation Report. Roofing Industry Committee on Weather Issues, Inc., Powder Springs, Ga., 260 pp.
2 RICOWI, Inc. and Oak Ridge National Laboratory, 2007: Hurricane Katrina Wind Investigation Report, Roofing Industry Committee on Weather Issues Inc., Powder Springs, Ga., 202 pp.
3 RICOWI, Inc., 2018: Hurricane Michael Wind Investigation Report. Roofing Industry Committee on Weather Issues, Inc., Powder Springs, Ga., 159 pp.
4 Giammanco, I.M., E. Newby, and W.H. Pogorzelski, 2023: Observations of building performance in Southwest Florida during Hurricane Ian (2022): Part I Roof cover damage assessment on residential and light commercial structures. Insurance Institute for Business & Home Safety (IIBHS). Technical Report, 26 pp.
5 See note 4.
6 RICOWI, Inc., 2018: Hurricane Ian: Storm Investigation Program. Roofing Industry Committee on Weather Issues, Inc., Powder Springs, Ga., 132 pp.
7 ANSI/SPRI. 2022. Wind Design Standard for Edge Systems Used with Low Slope Roofing Systems, ANSI/SPRI/FM 4435 ES-1
8 Giammanco, I.M., E. Newby, W.H. Pogorzelski, and M. Shabanian, 2023: Observations of building performance in Southwest Florida during Hurricane Ian (2022): Part II Performance of the modern Florida Building Code, Insurance Institute for Business & Home Safety, Technical Report, 21 pp.
9 See note 7.
10 Sanders, C., K. Parackal, and M. Morrison, 2024: Full-scale wind loads on flashing edge metal systems, J. Wind. Eng. Ind. Aerodyn., In preparation.
11 Insurance Institute for Business & Home Safety, 2024: Rating the States: Hurricane Coast. IBHS Technical Report, 25 pp.
12 Graham, M. S., 2009: Understanding ANSI/SPRI ES-1, Professional Roofing, 39 (10). professionalroofing.net/Articles/Understanding-ANSI-SPRI-ES-1–10-01-2009/1573
13 See note 4.
14 FM
15 Insurance Institute for Business & Home Safety, 2022: IBHS FORTIFIED Commercial Wind Standards. Technical Document, 69 pp. fortifiedhome.org/wp-content/uploads/Fortified_Commercial_Standard-2022-v4.pdf
16 Insurance Institute for Business & Home Safety, 2022: IBHS FORTIFIED Multifamily Wind Standards. Technical Document, 61 pp. fortifiedhome.org/wp-content/uploads/Fortified_Multifamily_Wind_Standards_2022.pdf
David Balistreri and Derek Hodgin are members of the RICOWI board of directors; Dr. Ian Giammanco is the managing director for standards & data analytics and a lead research meteorologist at the IBHS Research Center in Richburg, S.C.; Chuck Miccolis is managing director of commercial lines for IBHS; and David Roodvoets is a member of several RICOWI committees.
