Reroofing an Icon Is a Moving Target; A Case Study of the Reroofing of the Rogers Centre Christopher DeRosa, PEng, AIA Walter P Moore & Associates 1747 Pennsylvania Ave. NW, Ste. 1050, Washington, DC 20006 • 202-481-8726 • cderosa@walterpmoore.com Ping Mu Walter P Moore & Associates 128 Degrassi Street, Toronto, ON M4M 2K6 David T. Ford, RRC, RWC, PEng, PE, LEED AP Walter P Moore & Associates 1100 Walnut St., Ste. 1825, Kansas City, MO 64106 816-701-2118 dford@walterpmoore.com Building Enclosure Symposium • NovembeBEr 11-12, 2019 D DeRosa, Mu & Ford • 121 Abstract Assessing, designing, and overseeing the roofing replacement of a retractable roof stadium is an uncommon project. The Rogers Centre, originally named the Skydome, is currently home to the Toronto Blue Jays Major League Baseball team. The climate and location implications of this project were also unique. Rogers Centre is located on the north shore of Lake Ontario. The 1800-ft.-tall CN Tower is immediately adjacent and hovers above the roof surface. Ice “missiles” breaking off from the tower have historically impacted the roof surface. These factors influenced the design of the new roofing system. In this presentation, we will discuss the challenges and complexities encountered during this project, which began in the assessment phase. 3-D laser imaging, infrared thermography, cores, and exploratory openings were employed to determine the extent of membrane and substrate damage, the location of moisture infiltration through the original roofing membrane, and membrane attachment detailing at edge conditions. Due to the geometry of the roof and its location, the roof sees harsh winter conditions for several months. Ice and snow collect and settle at the gutters, putting significant stress on the eaves. In addition to updating and strengthening the eave design from the original, a customized snow melt system was designed and installed. In this presentation, these and other challenges encountered throughout assessment, design, and construction oversight will be discussed. Speakers Chris DeRosa CHRIS DeROSA is an engineer and registered architect in the Diagnostics Group of Walter P Moore, with a special focus on building enclosure consulting. He has more than nine years of experience in the field of forensic engineering. DeRosa’s expertise includes evaluating and designing repairs for distress related to clay masonry, stone façades, concrete structures, building enclosure moisture management, roofing systems, and below-grade waterproofing on concrete substrates. As a licensed architect, DeRosa uses his design expertise to collaborate with architectural teams on new construction, restoration, and renovation projects. He has also developed work scopes, repair details, repair procedures, and technical specifications for waterproofing, restoration, and rehabilitation projects. Ping Mu PING MU is in the Diagnostics Group of Walter P Moore, and focuses on building enclosure consulting and building diagnostics. Mu’s expertise includes evaluating, assessing, and designing repairs for distress related to exterior wall assemblies and roofing systems; historical building façade assessment and rehabilitation; parking garage assessment and repair; load checks for existing structures; and building performance modeling. She routinely develops contract documents, including drawings and technical specifications, as well as providing construction administration. Nonpresenting Coauthor David T. Ford, RRC, RWC, PEng, PE, LEED AP 122 • DeRosa, Mu & Ford Building Enclosure Symposium • NovembeBEr 11-12, 2019 INTRODUCTION The Rogers Centre, formerly known as the SkyDome, is a world-class entertainment facility located along Toronto’s Lake Ontario, adjacent to the CN Tower. When Rogers Centre opened in 1989, it was the first stadium in North America with a motorized fully retractable roof. With this feat in engineering excellence, it allowed the stadium to go from an open-air venue to a closed one in 23 minutes. Rogers Centre has served as a critical cultural and community center for the city, hosting Major League Baseball and Canadian Football League games, as well as a variety of music, trade, and community events. Now after 30 years and thousands of events, the Rogers Centre’s roofing needs to be replaced. Given the importance of the roof to the overall operations of the venue, Rogers Communications and the Toronto Blue Jays have pursued the restoration of the roof as the Rogers Centre continues to serve as the cultural center of Toronto (Figure 1). The project began by assessing the existing conditions of the roof system and potential options for a roofing replacement. An initial feasibility study was performed in December 2014 to explore alternate roofing systems that could be utilized in lieu of a replacement of the existing roofing assembly. A more detailed conventional roofing replacement investigation was performed in October 2016 to further assess the detailing of the existing roofing and considerations for its replacement with a similar system. In 2017, an additional study was commissioned to explore hybrid options where the majority of the roofing would be replaced with polyvinyl chloride (PVC) membrane and select portions would be replaced with ethylene tetrafluoroethylene (ETFE) to allow for natural light within the facility. It was through these investigations that a greater understanding of the current condition of the roof and how the replacement would align with the overall development of the stadium was achieved. It was ultimately determined that a strategic replacement of the roofing with a new PVC membrane roofing system was the option that would best serve the Rogers Centre. ROOF DESCRIPTION The roof of the Rogers Centre is roughly circular in plan and composed of four separate panels, of which three are moveable and one is stationary. The layout of the panels in the closed position is provided in Figure 2. Reroofing an Icon Is a Moving Target; A Case Study of the Reroofing of the Rogers Centre Building Enclosure Symposium • NovembeBEr 11-12, 2019 D DeRosa, Mu & Ford • 123 Figure 1 – General view of the Rogers Centre’s roof open. Figure 2 – Roof panel layout in closed position. In the closed position, Panel No. 1 is a quarter dome located at the southern end of the stadium and is supported on a series of circular steel tracks. Panel No. 2 and Panel No. 3 are barrel vaults, which are supported on independent sets of linear steel tracks that run north-south on either side of the stadium bowl. Panel No. 4 is a stationary quarter dome panel located at the northern end of the stadium. When the roof is in the open position, all the roof panels nest at the northern end of the stadium above the fixed location of Panel No. 4. To accommodate nesting, each of the roof panels is supported at a different elevation as shown in Figure 3. The stadium has parapets along its perimeter, creating gutters of various geometries and sizes below each of the roof panels’ lower eaves. The gutters are critical during the winter, when large amounts of snow slide off the stadium roof and collect in these gutters. ORIGINAL ROOFING SYSTEM Each of the four roof panels is supported by steel trusses of tubular steel members and decking. The original roofing system was assembled with underside acoustic insulation. The insulation was adhered to the underside of the deck and secured with metal bands. Placed directly over the metal roof deck is a vapor retarder—a low-density polyethylene membrane with all the joints sealed with butyl tape. Thermal insulation, 44.5-mm-(1.75-inch-)thick trilaminate-faced polyisocyanurate, was mechanically attached with screws and stress plates to the metal deck. The PVC roofing membrane was installed over the insulation. The membrane was 48-mil reinforcement membrane with heat-welded seams, mechanically battened to the roof deck. Each of the panels has intermediate sheet metal snow diverters that were covered with PVC flashing. The typical roofing assembly is provided in Figure 4. INVESTIGATION AND ANALYSIS As part of the investigation, the original stadium construction drawings were reviewed in an effort to fully understand the existing roofing system and key details at transitions, terminations, and anchorage. Additionally, a 3-D laser scan of the roof was conducted to quantify roofing system components and obtain accurate documentation of the roof’s complex geometry. Aerial thermographic imaging was performed using drones to get an overall thermal mapping of each section of each roof panel. This provided a general understanding of the patterns of potential water-infiltrated areas within the roofing assembly. Using the initial aerial thermographic imaging as a reference, more detailed thermographic imaging was performed of the entire perimeter of the roof. Exploratory roofing openings were made at various strategically chosen locations of each panel, including terminations of each panel, potential wet assemblies as indicated by the aerial thermographic imaging, and locations in the field of the roof at different distances from the eave. The roof cuts confirmed the results of the thermographic imaging. The roofing openings provided direct information on the condition of the existing roofing assembly’s various components. It supported and validated findings from thermographic imaging at these select roof opening locations. Coupled with the openings, the thermographic imaging provided information of the likely extent of certain conditions within the roofing assembly, such as wet insulation board. In the field of the roof panels, the condition of the roofing membrane was what would have been expected of a roof of this age. The PVC membrane thickness above scrim was insufficient to provide Figure 3 – Roof panels section view (north-south) in closed and open position. Figure 4 – Typical existing roofing assembly in the field of roof panels. 124 • DeRosa, Mu & Ford Building Enclosure Symposium • NovembeBEr 11-12, 2019 protection of the scrim. There was evidence of plasticizer loss and membrane embrittlement at various locations. As a steep-sloped roof, the PVC membrane was experiencing friction, abrasion, and wear from the snow accumulation sliding down the surface in the winter season. The wearing was the most obvious at the lower part of the panel where it experienced the greatest amount of sliding snow (Figure 5). There were numerous repair patches throughout Panels No. 3 and 4 caused by ice falling from the adjacent CN Tower. Not only were snow and ice falling from the perimeter roof of the circular deck near the top of the tower, but ice also formed on the vertical surface of the concrete tower body. This ice would form under certain weather conditions when the temperature fluctuated between just above and below freezing. In these conditions, spears of ice would form and then fall from the tower, often resulting in the membrane being pierced, and in some instances, causing damage to the metal deck. Despite the isolated areas damaged from the ice fall, the insulation board was generally dry and in serviceable condition in the upper portions of the roof panels. The metal decking was also generally in fine condition with no corrosion observed at any of the roof exploratory openings. At the eaves of the roof panels, the roofing assembly condition was much worse. Besides the aging of the roofing membrane, roof openings indicated that the insulation at the perimeter of the roof had experienced prolonged exposure to moisture at all panel locations. Vapor barrier weathering was also observed at various locations where it had been exposed to moisture at the roof perimeters. Furthermore, pulled-out fasteners at the eaves of the roofs were observed on the west side of Panels No. 2 and 3. Roof openings at these locations indicated damaged roof decking and edge enclosure sheet metal at the eave edge, which in turn could not function as adequate support for the roofing system above, as illustrated in Figure 6, especially under prolonged snow and ice exposure. As noted, the moisture accumulation was consistent at the eaves of the roof at all panels. Water accumulation was likely due to condensation underneath the roofing membrane traveling to these locations, as well as water infiltration at isolated locations of PVC membrane punctures, caused by the falling ice from the CN Tower. The vapor barrier in the roofing system was not detailed to be an air barrier due to the Figure 5 – Accumulation of sliding snow at the eave of Panel No. 3. Figure 6 – Roof exploratory opening section view at existing roofing assembly at eave of panel 2. Building Enclosure Symposium • NovembeBEr 11-12, 2019 D DeRosa, Mu & Ford • 125 nature of the attachment to the metal deck. Warm air inside the dome rises to the roof, and the moisture within the air condenses at the cold roofing membrane. Water from the condensation runs along the top facer of the insulation board down the sloped roof and accumulates at the roof eave. The typical roofing assembly along the perimeter is provided in Figure 7. The pulled-out fasteners and damaged sheet metal enclosure pieces at the roof eave are due to snow loading at these roof panels. Snow sliding down from the roof panel accumulates in the respective roof panel’s gutters. Due to the limited size of the roof gutter, snow accumulation at the gutter often extends more than 10 feet up onto the eave of the edge of the roof. This snow is often a mixed, condensed, icy, and watery composition, placing a significant loading onto the eave structure, as illustrated in Figure 8. ROOFING REPLACEMENT DESIGN Based on the condition of the existing roofing system and the construction schedule required by the client, a full roofing membrane replacement was recommended with limited insulation and vapor barrier replacement. The insulation and vapor barrier replacement mainly occurred along the eave of the roof panels. The replacement roofing membrane is an 80-mil PVC, which is almost twice as thick as the original 48-mil PVC membrane. The overall roofing anchorage system stays the same as a mechanically fastened system, using the linear battens. The batten spacing remains the same after a back-check analysis of the wind pressures from the original wind tunnel study against current building codes. Figure 9 – Roof panel eave edge detail. Figure 7 – Typical roofing assembly perimeter condition. Figure 8 – Snow accumulation in the roof gutter. 126 • DeRosa, Mu & Ford Building Enclosure Symposium • NovembeBEr 11-12, 2019 There were two significant issues with the original roofing system at the roof eave. One was the inadequate roof decking support for the roofing system to resist the load from snow accumulation at the eave. Another issue was the water accumulation at the eave, causing the roofing components to see extended water exposure. To enhance the details at the roof eave, two improvements were accordingly designed for the replacement system: strengthened roofing system support and a drained eave detail as shown in Figure 9. In the original detail, the sheet metal enclosure at the roof decking eave termination would be adequate for regular snow load at the roof if there were no snow accumulation at the eave. However, with the typical snow loading at the eave, a more substantial (thicker-gauge) support is required to fill the void inside the sheet metal enclosure in order to reduce the likelihood of future deformation of the system under snow loads. In the roofing replacement detail, a stiffener is added under the sheet metal enclosure to resist the accumulated snow load at the eave (Figure 10). For the water and moisture management within the roofing assembly, a drainage system was designed at the roof eave. Since the majority of the existing insulation board and vapor barrier will remain in place, moisture infiltration from inside the dome and condensation at the interface between the roofing membrane and the top facer of the insulation board are expected to continue to occur. With the existing detailing at the roof eave, the condensation water rundown was trapped within the roofing assembly, causing premature deterioration of the roofing components. The replacement detail incorporated measures to provide drainage and reduce the likelihood of future moisture entrapment. In preparation of the drawings of the construction documents, plan views, elevation views, and section views were included to clearly convey the extent of the roofing replacement. Both demolition sheets and reroofing sheets were provided for the different views to further define the scope of the project. Considering the tight construction schedule, each panel had individual drawing sheets for ease of separation if multiple roofing contractors were required for the construction. For Rogers Centre, no termination details are typical. For the detail drawings, both existing conditions and final replacement conditions are presented that provide clear callouts as to which components are to remain and which components are to be replaced and how they are to be replaced. Working with the roofing membrane manufacturer, we aimed at providing a functional and watertight replacement system. In the preparation of roofing replacement drawings, details were provided for every possible condition of the project to reduce the number of unforeseen conditions during construction, which is common when working on an existing building. For specification of the construction documents, the roofing replacement scope was broken down into detailed task items for each panel so that a detailed bid form could be generated for individual roof panels. Items such as damaged insulation board replacement in the field zone of the roof were listed under unit price to assist the client with an accurate construction cost tracking. CONSTRUCTION With a project of this unique nature, there were many challenges associated with the application of the roofing replacement and maintaining a high level of quality control. The geometry of the roof, with its barrel-arched central panels and half-domed outer panels, meant that the majority of the roof was only accessible with swing stage, rope access, or ladders. In general, all of the roofing material removed and installed needed to be transported by swing staging. This meant observation of the work by consultants was limited. Due to the facility’s position next to Lake Ontario, the weather had the potential to dramatically change Figure 10 – Installation of sheet metal to reinforce the roof eave edge. Figure 11 – Roofing replacement on Panel No. 3. Building Enclosure Symposium • NovembeBEr 11-12, 2019 D DeRosa, Mu & Ford • 127 (Figure 11). Fluctuations in temperature, precipitation, humidity, dew point temperature, and cloud cover had a dramatic impact on the roofing application. Lastly, with two roofing contractors and multiple crews working simultaneously, there was the challenge to maintain consistency and quality. (See Figures 12-14.) Prior to the start of the project, the team established a quality assurance plan, which included engineered shop drawings, full-scale mock-ups, preparation of quality control check procedures, and field reviews by multiple parties. More than 15 in-situ mock-ups were installed at the different transitions and unique roof conditions. The mock-ups were made with the exact construction techniques and materials that were used on the project. The mock-ups gave the consultants, contractors, manufacturers’ representatives, and the owner the opportunity to assess the roofing replacement so that the quality of the installation and end product could be evaluated. With the mock-ups, the project team was able to foresee problems and solve them before they happened on a large scale. Since this was not a full roofing replacement, the assessment of each of the roofing components to remain was critical. Any deterioration to these components could undermine the performance of the new assembly and its structural integrity. For instance, if the existing rigid insulation had entrapped moisture or physical damage, it could prevent the membrane from adequately attaching to the roof deck. Subsequently, an evaluation protocol was developed for the roofing contractors to review the existing roof insulation that allowed the contractors to determine whether the insulation needed to be replaced. Furthermore, each of the contractors performing these evaluations had digital tablets to document the completion of the protocol and photograph existing conditions so that the entire team could follow the progress. This resolved the Figure 12 – Roofing replacement on Panel No. 1. Figure 13 – Roofing replacement on Panel No. 3. Figure 14 – Roofing replacement on Panel No. 2. 128 • DeRosa, Mu & Ford Building Enclosure Symposium • NovembeBEr 11-12, 2019 design consultants’ desire to evaluate all the existing components prior to installing the new system while maintaining the contractors’ desire to complete sections of the new roofing efficiently. The weather at the stadium had the potential to be extreme and dramatically change. These changes had an impact on the application of the membrane. For the heat welding of the membrane, the roofers adjusted the weld equipment temperature, speed, and airflow depending on the conditions. These adjustments were critical to achieve good quality of the finished seam. The quality of the welds were further verified as soon as the seams cooled. After welding, a blunt tool was run along the seam edge. Any penetration of the probe into the seam indicated a void in the weld that must be repaired. All welded seams were tested for integrity and continuity. In addition to probing, seam samples were taken to verify the quality. CONCLUSION The replacement of the Rogers Centre roofing was scheduled for substantial completion in September 2019. Due to the unique nature of this project, it offered many challenges. The team was able to overcome them by developing unique approaches to the investigation, design, and application of the new roofing systems that were customized for the Rogers Centre. However, even with the most well-thought-out project plan, unforeseen conditions still developed. At those times we needed to work closely with the project team and be flexible to adjust the work process to keep the project progressing while maintaining the highest level of quality. ACKNOWLEDGEMENTS Walter P Moore would like to offer special thanks to the Toronto Blue Jays, WSP Global Inc., EllisDon, Dean Chandler Roofing, and Flynn Canada. Building Enclosure Symposium • NovembeBEr 11-12, 2019 D DeRosa, Mu & Ford • 129
