Post-Katrina Study Notes Durability of Asphalt Roofing Systems Under Extreme Conditions, Says Asphalt Roofing Manufacturers Association
RICOWI Wind Investigation Program Yields Valuable Insights, Identifies Successful Applications along with Failure Mechanisms
[Washington, DC] –The Hurricane Katrina Wind Investigation Report, recently released by the Roofing Industry Committee on Weather Issues (RICOWI) Inc., provides valuable insights into installation techniques that can enable asphalt roofing systems to better withstand major windstorms, according to the Asphalt Roofing Manufacturers Association.
“ARMA applauds the investigations carried out by RICOWI in cooperation with Oak Ridge National Laboratory,” says Reed Hitchcock, Executive Director of ARMA. “Such surveys allow the industry to evaluate the performance of materials and designs in real world constructions subject to extreme conditions created by Nature.”
RICOWI is comprised of all of the major roofing associations and includes members of academia, educational and testing facilities and others involved in the science of roofing. The mission of the Wind Investigation Program (WIP) is to investigate the field performance of roof assemblies after major wind storm events, factually describe roof assembly performance and modes of damage, and formally report results of investigations and damage modes for substantiated wind speeds.
Hurricane Katrina made landfall as a rare Category 4 Hurricane (defined as having winds from 131 to 155 miles per hour). In its aftermath, WIP teams focused on Coastal regions in Mississippi from Bay Saint Louis to Pascagoula, which experienced winds in the 120 to 130 mph range.
WIP teams surveyed about thirty low-sloped asphalt commercial roofing systems, including 16 modified bitumen (MB) and 14 built up roof (BUR) systems. Most of these systems experienced little or no damage, usually limited to edge details and minor scouring. When major damage was noted, it was typically due to a poorly attached system components such as decks or cementitious wood fiber (CFW) panels. The report results stressed that all members of a composite system must be adhered or fastened to resist uplift. The investigators attributed a single case of poor adhesion to an installation defect, i.e., not preparing the concrete with a suitable primer.
The investigators also reported on steep-sloped asphalt shingle roofs, including eight made with three-tab asphalt shingles and three made with laminated asphalt shingles. Many of these roofs experienced only minor damage. According to the report, in those cases where significant damage did occur, it could have been eliminated if the construction methods were consistent with the latest codes.
For examples, shingle patterns such as racking, with omitted fasteners, resulted in excessive shingle loss. Also, shingle loss was pronounced around dormers and chimneys and other areas of increased wind intensity. The flashing and detailing of eaves and gutters also require attention. In a few cases, major roofing damage accompanied structural damage from wind pressurization, such as through gable ends.
“Considering the range of installation quality, we are generally pleased with the wind performance of the asphalt roofing materials at extreme wind speeds, for both the low slope and steep slope applications,” says Hitchcock. “The many surviving roofs are a tribute to the quality of the materials and the craftsmanship of the roofers. The lessons learned are that substandard system designs and poor installation practices can not be tolerated in hurricane zones or any areas prone to extreme windstorms.”
The complete report titled “Hurricane Katrina Wind Investigation Report” (September 2007) is available from RICOWI, Inc. A similar report generated in the aftermath of previous major hurricanes titled "Hurricanes Charley and Ivan Wind Investigation Report” (March 2006) is also available for comparison. These reports include damage surveys for all major roofing systems and materials. They can be downloaded in PDF format from RICOWI's Web site, www.ricowi.com.
The ARMA publication titled “New Wind Standards for Asphalt Shingles” is available from the ARMA Web site (See www.asphaltroofing.org/resources_publications_arma.html.) For additional information concerning ARMA, their programming and activities, contact ARMA at (202) 207-0917; fax (202) 223-9741; or visit the ARMA web site atwww.asphaltroofing.org or www.qualityasphaltroofing.org.
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About the Asphalt Roofing Manufacturers Association
The Asphalt Roofing Manufacturers Association (ARMA) is the North American trade association representing the manufacturers and suppliers of bituminous-based residential and commercial fiberglass and organic asphalt shingle roofing products, roll roofing, built-up (BUR) roofing systems, and modified bitumen roofing systems.