The 2004 Florida hurricanes presented a set of unique wind-event opportunities allowing teams of Roofing Industry Committee on Weather Issues (RICOWI) investigators to fan out over the storm battered Sunshine State and examine more than 50 single-ply roofing systems that either failed, were damaged, or remained intact. The study was jointly funded by the roofing industry and the Department of Energy (DOE), which takes an interest in determining whether energy efficient roofing materials advocated by the federal agency will also work well in severe wind events. David Roodvoets, a RICOWI Wind Event Coordinator who is also a technical director for the Single-Ply Roofing Industry (SPRI) headed the study for the trade association.
For TFM‘s coverage of last year’s hurricane events, see “Worst Case Scenario” from the archives.
“Many people claim that as buildings become more energy efficient they also are more susceptible to damage,” said Andre Desjarlais with the Oak Ridge National Laboratory in Tennessee and member of the RICOWI team. He noted this was not found to be true, however, because it turns out that more energy efficient buildings were also better designed structures. That was just one preliminary finding by RICOWI, because the overall mission was to document the performance and damage that occurred to roofing systems during substantiated hurricane-level wind speeds.
To investigate category four Hurricane Charley following its landfall Friday, Aug. 13, 2004, near Punta Gorda, seven teams of investigators were deploy to conduct 90 inspections from Aug. 18-21. To investigate category three Hurricane Ivan after landfall Sept. 16 near Gulf Shores, Alabama, another five teams were deployed to conduct 75 inspections from Sept. 22-25.
All types of low slope and steep slope roofs were part of the study, including roofing systems with SPF, TPO, BUR, EPDM and Vinyl membranes, he explained. Three attachment methods were studied — mechanical, adhesive and ballasted — but all combinations of membrane and attachment types were not available in the field. The team studied approximately 24 single ply roofing systems and was limited only by what was available to for inspection in the field, and the time allotted for data collection and completing the study.
Marketing and pricing of the membranes had a significant influence on the available products to study. For example, the Punta Gorda area contained a significant amount of vinyl roofing membranes, which coincidently performed very well. That was just another of the ancillary observations and findings.
RICOWI’s preliminary results were recently presented by Roodvoets and Desjarlais to SPRI. The earliest findings contained information about six possible roofing systems in the path of the storms. A full report on every roof inspected is set to be released in October.
“The study was somewhat opportunistic for low slope roofs. We tried to concentrate on essential facilities such as shelters, schools, hospitals, fire, municipal and postal facilities,” Roodvoets said.
The RICOWI teams of investigators selected areas where significant damage was expected and some areas where damage was not expected to be seen. For the steep slope roofs where damage is more easily observed from the street, the investigators looked at the same buildings, but expanded to residential facilities. None of the roofing systems investigated were immune from damage but patterns developed after analysis of the inspection reports.
Buildings closest to the ocean were not inspected because their structural integrity may have been compromised by water damage experienced during the storm surge. In many cases, the remains of coastline buildings were only evident by piles of rubble and such remains were beyond the scope of the RICOWI study. This was because the focus was on roofing performance in a wind event, and not a water event.
“Failure of roofing systems was because of system failure at the perimeter, and punctures and tears from debris,” Roodvoets said. “The membrane attachment to the deck cannot resist the loads created when the perimeter securement fails, and this leads to progressive loss of membrane coverage.”
An example of a roof failure studied includes a Port Charlotte office building that had a poorly installed roof. Investigators found that the roof system’s poor performance was the result of inconsistent clip installation and during the wind event an intensely high clip load occurred and eventual pull off failure occurred to the membrane.
The overall findings were that post-Andrew roof designs and installations performed well unless there were installation problems; internal pressurization from openings, typically created by failed accessories; perimeter detachment; and corrosion issues.
Desjarlais noted: “It’s a fair statement to say membranes themselves were not the major cause of failure. There were a lot of perimeter attachment failures. If you can’t hold the edge down, no matter what kind of roof you have the whole thing is going to come down.”
“The issue of fastener corrosion was seen over and over again,” continued Desjarlais, noting coastal specifications should specify fasteners with coatings that are unaffected by the salt air environment.
Windblown missile damage to roofs was insignificant, according to Desjarlais. Membrane damage was typically limited to punctures from lightening rods and wire that swung in the typhoon-speed winds and whipped the membrane with sharp metal edges. The poorly attached 2,000 pound HVAC units rolling over the roofs also punctured membranes in a few cases. But panels and parts of the HVAC were more commonly blown off the units by the wind and across roofs because the equipment was not properly tied down either during installation or following ongoing servicing.
On some single ply systems, the damage was easier to locate and this may be an advantage to those types of systems, Dejalais said. Conversely, it was less obvious to determine damage on systems such as ballasted roofs because the small stones covering them can conceal the indicators of compromised performance.
Another factor affecting roof performance, which was anticipated, was intensely high speed winds entering buildings through openings such as shattered windows and open doors. How tightly sealed a building remained during the hurricanes often determined the fate of the roof and in some cases the entire structure. Some roofing membranes were compromised after walls or windows were damaged providing uplift to the roof in excess of what the building was designed to endure.
Buildings built after Hurricane Andrew performed 100 times better than buildings with roofs installed before Andrew, according to Desjarlais.
Before Hurricane Charley, the last recorded storm to make landfall in Punta Gorda did so in 1943, and many of the older buildings there had been through the previous storm. Furthermore, the financial resources available to building owners in Punta Gorda appeared to be limited because of indications that the roofs seen by the inspections teams had been poorly maintained.
“What we saw was a lot of deferred maintenance that compromised the roofing system,” Desjarlais said.
But not every roof on every building in the path of Charley. A Punta Gorda Elementary School was well designed and its roofing system installation and performance were both good.
The other team of inspectors also looked at an academic building in the Panhandle. The roof on a Pensacola school building, identified as No. 2, was damaged. The key points that surfaced from the investigation were that damage was initiated by pressurization and billowing at overhangs. This windblown phenomenon caused cleat deforms and disengages
of the edge metal.
Other findings were that the cleat gauge was less than currently recommended by FM Global LPDS 1-49 and ANSI/SPRI ES-1. In addition, corrosion of roof edge fasteners contributed to expansion of edge damage into field.
A second school building inspected in Pensacola had damage and propagation. The edge metal was bent upward, nailers lifted, membrane base sheet tore around fasteners and peeled back.
On closer inspection, the edge metal gauge and nailer securement was also less than currently recommended by FM Global LPDS 1-49 and ANSI/SPRI ES-1, and the lack of enhanced perimeter base sheet fastening contributed to propagation of edge damage into field area.
According to another RICOWI inspection team member Peter Garrigus, vice president of engineering for Trufast Corp. in Bryan, Ohio, “The corrosion problems were due to the wrong roofing products” for the a hostile atmosphere along the coast.
Addressing the consistent failure of roofing clips and fasteners, Garrigus explained, “It really boiled down to workmanship and proper application of materials.”
The roofing systems performed the way there were supposed to perform in cases where the right fasteners and roofing assembly were applied in accordance to the manufacturers requirements, Garrigus observed.
In nearly 95% of the cases studied where roofing system failure was seen, the problems were because of poor workmanship and substituted materials, explained Garrigus, who had made similar observations before during inspections conducted after hurricanes Hugo and Andrew in years past.
In some cases, nails from a local hardware stores were purchased, brought to the job site and used to replace J-bolts or other proper fasteners. In addition, the nails were often spaced improperly and at less frequency along the roof’s perimeter than was called for by the manufacturers of the proper fasteners. And in other cases, the fasteners often were placed into non-pressure treated lumber causing them to rust.
Garrigus believes roofs as poorly constructed as those that failed during hurricane force winds could have failed in lower than hurricane speed winds. To counter installation and material problems, Garrius suggested the trend toward manufacturers offering contractor training programs should be accelerated. Also, roofing inspections during application either by the suppliers or a roofing consultant would further decrease roof system failures during high wind events.
The education of entire building teams also would benefit roofing assemblies because of the deleterious effects to the roof assemblies seen as a result of pressurization within the building as seen during the 2004 Florida hurricane season. The effects compromised openings in buildings can have on both the roof and the structural integrity of the building were catastrophic in many cases and therefore building teams need to install impact resistant doors and windows to seal the interior from the balloon effect that pressurization has on a building.
Many coastal property owners housing docking and transportation operations simply left doors open on their warehouses and lost entire buildings, according to Garrius. So property management is also an issue. The RICOWI field performance investigation of roofing assemblies was conducted on roofs with the unfortunate fate of being in the paths of hurricanes Charley or Ivan during the hurricane season lasting from June until November in Florida.