Low-Slope Lessons from 30 Years of Hurricane Events Aaron R. Phillips Asphalt Roofing Manufacturers Association (ARMA) | Washington, DC aphillips@asphaltroofing.org Chadwick Collins Asphalt Roofing Manufacturers Association (ARMA) | Washington, DC ccollins@kellencompany.com IIBEC International Convention & Trade Show | SeptembeBEr 15-20, 2021 P Phillips | 171 Aaron R. Phillips Asphalt Roofing Manufacturers Association (ARMA) | Washington, DC Aaron R. Phillips, vice president of technical services for the Asphalt Roofing Manufacturers Association (ARMA), has worked in the asphalt roofing industry since 1988. His career began at TAMKO Building Products LLC, where he worked in research and development and technical services. Throughout his career, Phillips has been active in various industry organizations, including more than 25 years of service as an ARMA volunteer. Nonpresenting Chadwick Collins author: Asphalt Roofing Manufacturers Association (ARMA) Washington, DC Chadwick Collins’s entire 15 year career has been on the technical side of the roofing industry, ranging from field technical services to product and system testing along with code and standard development. His experience comes from working for two manufacturers and an engineering consulting firm prior to joining the Asphalt Roofing Manufacturers Association’s (ARMA’s) team. He holds a bachelor of science in mechanical engineering, was previously a Registered Roof Observer, and is currently a licensed drone pilot and member of ASTM, ICC, and IIBEC. 172 | Phi l l ips II BEC International Convention & Trade Show | September 15-20, 2021 ABSTRACT SPEAKER The Federal Emergency Management Authority (FEMA) deployed Mitigation Assessment Teams (MATs) after Hurricanes Irma and Michael impacted Florida in 2017 and 2018. Industry representatives, academics, regulators, insurers, and representatives of other interests all participated in the MATS, which were deployed in affected areas after the storms to study wind damage, report observations, and make recommendations on how to improve construction methods and help reduce the chance of damage from future storms. This presentation will review the recommendations from the MAT reports and show how high winds can impact construction. It will cover wind damage to roof assemblies, as well as water damage to structures and contents resulting from wind-driven rain, and focus on the specific recommendations from FEMA as well as the roofing industry response. Roof damage associated with hurricanes is not a new concept. Video footage and images showing catastrophic damage are commonplace in news coverage and social media posts, and detailed storm damage research reporting has become more commonplace in the past five decades. However, many people are not aware of, or do not fully understand, the process that the Federal Emergency Management Agency (FEMA) undertakes after a hurricane event with the deployment of Mitigation Assessment Teams (MATs). These teams are composed of participants from the construction industry, academia, regulators, insurers, and other stakeholders who deploy to affected areas after the storms to study building performance, report observations, and make recommendations on how to improve performance in future events through a variety of strategies, including product standards, education, installation techniques, and building inspections. The roofing industry continues to be a key participant in these MATs as well as a key area of focus for wind-related observations. Another important step that the roofing industry and other stakeholders have undertaken is reviewing the MAT reports and responding to recommended actions. HISTORY OF FEMA MAT REPORTS The process of deploying a MAT to evaluate building performance after a catastrophic event has been occurring for more than 30 years. These efforts are a result of a federal, state, local, and private sector partnership to pool resources to quickly assemble and deploy investigation teams. Going back to Hurricane Andrew in Florida and Hurricane Iniki in Hawaii, both in 1992, MATs have issued reports following hurricanes, flooding (Iowa in 2016), and man-made events (Oklahoma City bombing in 1996; World Trade Center in 2001) (Fig. 1). The developed recommendations and suggested mitigation activities are meant to lead to greater resistance to future hazard events. FEMA MAT PROGRAM INITIATIVES The MAT program provides a means for experts in construction materials, techniques, and performance to assess how building systems function during exposure in various disaster events, including tropical storms and hurricanes, tornadoes, flooding, earthquakes, snow loading, and terrorism events. FEMA draws these experts from the design community and also engages academics, regulators, manufacturers, builders, and other stakeholders to ensure broad participation from all aspects of the construction industry. The observations of the team members form the basis for the findings and recommendations in the reports and provide a path to improved building performance in future events. With each successive investigation, the FEMA MAT program can build on previous successes and assess how prior recommendations did or did not work. In the two and a half decades since the FEMA report on Hurricane Andrew,1 there has been an evolution in the focus of the findings and the recommendations. It is interesting to note the contrast in the technical guidance. As an example, the Andrew report cites structural design concerns that likely led to damage scenarios, but also notes the enclosure breaches that led to total building failure. The report identifies issues with product and material standards and workmanship, and also notes concerns about building department oversight from a plan review and inspection perspective and that “inadequate training of the inspectors and supervisors are factors that may have contributed to the poor-quality construction observed” after Andrew. The report also includes recommendations for improved performance based on concerns such as building materials and techniques, quality control, retrofit efforts, and code compliance. The report’s stated goal is to “enhance the performance of buildings in future hurricanes.” That goal set the table for building improvement after Andrew and for subsequent decades. While many of the Andrew report’s recommendations for improved code compliance and building materials improvements II BEC International Convention & Trade Show | September 15-20, 2021 P hi l l ips | 173 Low-Slope Lessons from 30 Years of Hurricane Events Figure 1. Timeline of Federal Emergency Management Agency Mitigation Assessment Team publications. Source: https://www.fema.gov/emergency-managers/risk-management/building-science/mitigation-assessment-team. The observations of the team members form the basis for the findings and recommendations in the reports and provide a path to improved building performance in future events. have been addressed, the opportunity to work towards future improvements remains. The industry response to windstorm events has shifted from maintaining the structural integrity of the building to avoiding damage to its contents from wind-driven rain and reducing the likelihood of business disruptions and the need for residents to relocate after an event as their home is being repaired or rebuilt. This shift has resulted in the new paradigm of resilient building design and the goal of keeping communities in place after natural disasters wherever possible. The MAT report on Hurricane Ivan (FEMA 489)2 included a field observation that the damage and peeling of metal edge flashing led to the blow-off of the modified-bitumen roof membrane on the Pensacola Naval Hospital (Fig. 2). The report noted that while the concrete deck limited water intrusion into the building, the blow-off created debris that damaged windows and antennae. Damage to the roof membrane that leads to issues with other systems is an important element of evaluating roofing response to wind events: water intrusion that damages the interior of buildings or destroys building furnishing or contents is one of the more costly impacts of roof damage. The damage or removal of rooftop equipment, including heating, ventilation, and air conditioning (HVAC) and solar photovoltaic assemblies, can also result in breaches in the roof membrane. Once breached, the membrane can be subject to further damage or blow-off, and the openings in the roof assembly created when rooftop equipment is damaged can certainly lead to water intrusion. Figure 3 from the MAT report on Hurricane Harvey in Texas (FEMA P-2022)3 illustrates how damage to rooftop HVAC systems can result in punctures of roof membranes. The Harvey MAT report also notes concerns regarding the vulnerability of rooftop solar equipment subjected to high winds; this is also a steep-slope issue. The report recommends conducting a wind vulnerability assessment of the roof before installation of rooftop equipment on existing buildings. While many design requirements are easily addressed during the design and construction of roof assemblies on new buildings, retrofitting often adds additional complexities and challenges. FEMA’s U.S. Virgin Islands (USVI) Recovery Advisory 54 contains recommendations on the design, installation, and maintenance of solar equipment on existing buildings. One clear example of the industry response regarding damage assessments of low-slope roofs is the development of ANSI/SPRI/FM 4435/ES-1.5 The findings of MAT reports and other reported post-storm observations were key in identifying the edge securement of low-slope roofs as a critical design point and served as a catalyst for the development of the edge securement standard. The recognition of this industry work can be seen in the direct reference to ANSI/SPRI/FM 4435/ES-1 in the Hurricane Michael report: Recommendation #FL-23b. Copings and edge flashings should comply with ANSI/SPRI/FM 4435/ES-1 to prevent blow-off. The MAT observed many coping and edge flashing blow-offs. Blown-off copings and edge flashing can result in roof membrane lifting and peeling, and they can puncture roof coverings and cause other damage or injuries. This shows how the MAT reports interpret the damage observed. What would have been observed as a failure of the roofing system 30 years ago now not only identifies the key failure (edge securement) but acknowledges that the roofing industry has developed a methodology and has the products to address the issue in question and assigns the responsibility to other stakeholders. Figure 2. Damage to the Pensacola Naval Hospital in Florida from Hurricane Ivan. Figure 3. Roof membrane punctures from damaged heating, ventilation, and air-conditioning equipment on Rockport-Fulton Middle School in Rockport, Tex. Source: FEMA P-2022. 174 | Phillips IIiiBEC International Convention & Trade Show | September 15-20, 2021 HURRICANE MICHAEL IN FLORIDA FEMA’s latest MAT report was FEMA P-2077 on Hurricane Michael in Florida and was published on February 1, 2020 (Fig. 4).6 The pre-MAT deployed approximately two weeks after the event, with the 18-member MAT deploying from January 6 to 10, 2019, in Bay, Calhoun, Franklin, Gulf, and Wakulla Counties. The Michael report notes the 88-day delay between the pre-MAT and MAT resulted in the ability for the MAT to observe some sites and buildings initially observed by the pre-MAT to be lost. The report also notes that the desired response window for a MAT is 30 to 45 days following an event. This report follows the same format, breaking down the damage into two major categories: flood and wind. The MAT studied “the performance of non-residential buildings and facilities that had been retrofitted to improve building performance during high-wind events, as well as the performance of commercial buildings and non-retrofitted critical facilities. […]The MAT observed some damage to the MWFRS [main wind-force-resisting system] and building envelope systems at several different types of critical facilities and commercial buildings of varying age and size.”6 The following list summarizes the conclusions and recommendations that continue to be documented in MAT reports. • Inspections of building enclosure components are performed inconsistently, even though some jurisdictions require such inspections. • Improvements in wind calculations, uplift testing, and edge securement practices have proven effective in the ability of roofs to withstand expected design pressures. • Insufficient securement of rooftop equipment continues to be observed. This issue has expanded from HVAC and hoods to now include rooftop-mounted photovoltaic arrays. • Improperly installed products continue to be a source of roofing system failures. • There are particular issues with retrofits and re-covering/replacement installations where the main wind-force resistance systems or wind vulnerabilities were either not adequately assessed or addressed. • Damage from wind-borne debris, some originating from the roof, continues to be observed. BUILDING INDUSTRY STAKEHOLDER RESPONSE From the beginning, multiple building industry stakeholder groups have participated in the MATs and have used the reports to guide responsive actions. Through research initiatives, standards revisions and updates, educational programming, and proposed updates to model building codes, the industry response has provided a comprehensive and multipronged strategy to improve performance in and reduce damage from future storm events. While the MAT reports for Hurricanes Andrew and Iniki only provided conclusions for steep-slope roofs, later publications (such as Smith7) highlighted observations related to low-slope roofs. In fact, Smith estimates that more than 70% of roofs were significantly damaged during Andrew. Relative to low-slope roofs, primary items observed were the lifting and peeling of light-gauge metal edge flashings, wind-borne debris strikes, and failure of the main wind-force-resisting system members (such as decking and deck framing). Responses to these initial findings can be seen in the continual refinement of wind uplift calculations with updates to ASCE/SEI 7,8 the development and recognition in the code of ANSI/SPRI ES-15 to address metal edge securement and testing and work as recent as the approved table in the 2021 International Building Code (IBC)9 for parapet wall requirements for the use of roof aggregate, as mentioned at the end of the following section. These efforts from the industry have had the desired impact. Later reports indicate when these types of conditions are observed, the building’s original construction can be confirmed to have occurred before many of the guiding documents and code provisions were adopted into the building code. LOOKING FORWARD Wind-resistant construction techniques rely on the overarching design goal of providing a continuous load path that transfers the force of the wind from components and cladding through the main structural components of the building, through the foundation, and into the ground. Under this approach the various parts of the building act as part of a chain; damage to one link can result in the failure of the entire chain. As the Andrew report noted, damage to windows and doors led directly to total building collapse. As noted in the Michael report, for buildings designed and constructed in accordance with the 1995 and later editions of ASCE/SEI 7, breach of glazing or doors should not result in collapse from a design-level event. A breach may result in partially enclosed conditions, which could result in increased pressures, but the load/resistance factors or safety factors should be sufficient to avoid collapse. The chain analogy also applies to the recommendations of the MAT reports that contain a universal thought process. For buildings to perform during storms, we must start with proper design requirements; select materials, products, and systems to meet the design criteria; and include appropriate oversight to ensure that the proper construction techniques and installation instructions are followed. This means that building designers, manufacturers, contractors, and building departments all play a crucial role in the construction process. The industry has come a long way in improving building performance, but as we look to future enhancements, every link in that chain has to do its part. The following paragraphs address the previously summarized MAT report conclusions and recommendations. • Inconsistently performed inspections of building enclosure components, despite the requirements of some jurisdictions While inspections are in the purview of building code officials, industry stakeholders continue to create, update, and maintain reference and technical documents as well as eduFigure 4. Cover of the Federal Emergency Management Agency’s Mitigation Assessment Team report for Hurricane Michael in Florida. II ii B E C International Convention & Trade Show | September 15-20, 2021 P Phillips | 175 cation modules to inform inspection personnel of proper installation of products. • Insufficient securement of rooftop equipment (HVAC, hoods, rooftop-mounted photovoltaic arrays, etc.). Damage from impact of rooftop equipment has always been a part of MAT report observations. However, as uplift design and roofing system securement have improved, damage as a result of the effect of unsecured rooftop equipment has become more apparent. With the increased use of roofs for the installation of photovoltaic arrays, not only has the amount of potential equipment increased, the securement of that equipment is more vital. As such, functioning electrical generating equipment contributes to the ability of the building to become operational after an event. FEMA’s USVI Recovery Advisory 210 provides guidance to avoid equipment blow-off, and USVI Recovery Advisory 54 has specific information related to rooftop-mounted photovoltaic arrays. • Damage caused by improperly installed products Related to the need for inspections is the continued emphasis on proper installation. The IBC9 and the International Residential Code (IRC),11 along with many adopted code provisions, reiterate the need to follow manufacturers’ installation instructions. These, paired with the new training initiatives launched by several stakeholders, continue to highlight not only the need for proper installation, but the efforts by the roofing industry to address this issue. • Particular issues with retrofits and re-covering/replacement installations where the main wind-force-resisting systems or wind vulnerabilities were either not adequately assessed or addressed One of the fundamental accepted aspects of a building is that the building will typically outlast the roof installed on it. While roof re-covering or an entire roof replacement is anticipated, it not anticipated that an assessment and retrofit mitigation effort on the underlying structure is often not required by code. While many industry experts will point to the requirements of such an analysis in the International Existing Building Code,12 it is not as widely adopted as the IBC or IRC, which do not have the same assessment triggers. The Florida Building Code13 contains retrofit provisions for the assessment of existing buildings during reroofing. These provisions have been the subject of considerable debate in recent code adoption cycles in Florida as the Florida Building Commission addressed concerns about the need to balance technical feasibility with mitigation efforts while considering the cost implications to building owners. The concerns surrounding mitigation of existing buildings, particularly for critical facilities, has been considered an important part of post-disaster response. In fact, FEMA P-2062, Guidelines for Wind Vulnerability Assessments of Existing Critical Facilities,14 was released in December 2019. It provides designers with guidelines for assessing the vulnerability of critical facilities, and is a tool for building owners, design professionals, and regulatory entities charged with developing mitigation plans. • Damage from wind-borne debris, some originating from the roof Related to the securement of rooftop equipment, damage from wind-borne debris remains a two-fold issue for low-slope roofs. First, the resilience of the roofing system to withstand an impact continues to be a consideration that design and consulting professionals need to evaluate during system component selection. Second is when a roofing system could become the source of such debris, such as with ballast or loose aggregate. Even though the Florida Building Code requires embedment levels of rooftop aggregate, damage to surrounding buildings from loose or dislodged aggregate was observed during the most recent events in Florida. The roofing system in question did not have any parapet walls, which is at the very core of the recently approved code proposal to the IBC. This approved table provides guidance on the necessary parapet heights to mitigate aggregate blow-off based on wind speed, building height, exposure, and aggregate size. As this provision is adopted by more jurisdictions, as with previous improvements to the code, future events will allow side-by-side assessment of buildings built before and after the provision is in place. REFERENCES 1. FEMA (Federal Emergency Management Agency). 1992. Building Performance: Hurricane Andrew in Florida. FIA 22. Washington, DC: FEMA. 2. FEMA. 2005. Mitigation Assessment Team Report: Hurricane Ivan in Alabama and Florida. FEMA 489. Washington, DC: FEMA. 3. FEMA. 2019. Mitigation Assessment Team Report: Hurricane Harvey in Texas. FEMA P-2022. Washington, DC: FEMA. 4. FEMA. 2018. Rooftop Solar Panel Attachment: Design, Installation, and Maintenance. Hurricanes Irma and Maria in the U.S. Virgin Island, Recovery Advisory 5. Washington, DC: FEMA. 5. SPRI (Single Ply Roofing Industry). 2017. Test Standard for Edge Systems Used with Low Slope Roofing Systems. ANSI/SPRI/FM 4435/ES-1. Waltham, MA: SPRI. 6. FEMA. 2020. Mitigation Assessment Team Report: Hurricane Michael in Florida. FEMA P-2077. Washington, DC: FEMA. 7. Smith, T. L. 1994. “Causes of Roof Covering Damage and Failure Modes: Insights Provided by Hurricane Andrew.” In American Society of Civil Engineers (ASCE) symposium proceedings, Hurricanes of 1992: Lessons Learned and Implications for the Future, December 1–3, 1993, Miami, Florida, R. A. Cook, editor. Florida. New York, NY: ASCE. 8. ASCE. 2016. Minimum Design Loads and Associated Criteria for Buildings and Other Structures. ASCE/SEI 7. Reston, VA: ASCE. 9. ICC (International Code Council). 2020. 2021 International Building Code. Country Club Hills, IL: ICC. 10. FEMA. 2018. Attachment of Rooftop Equipment in High-Wind Regions. Hurricanes Irma and Maria in the U.S. Virgin Island, Recovery Advisory 2. Washington, DC: FEMA. 11. ICC. 2020. 2021 International Residential Code. Country Club Hills, IL: ICC. 12. ICC. 2020. 2021 International Existing Building Code. Country Club Hills, IL: ICC. 13. ICC. 2020. Florida Building Code: Building. 7th ed. Country Club Hills, IL: ICC. 14. FEMA. 2019. Guidelines for Wind Vulnerability Assessments of Existing Critical Facilities. FEMA P-2062. Washington, DC: FEMA. 176 | Phillips IIiiBEC International Convention & Trade Show | September 15-20, 2021
