University of Florida Researchers Believe Asphalt Shingle Roof Tile Installation Pattern Could Extend Adhesion Life
May 21, 2013
In order to allow for final research reports to be completed and submitted by June 15, 2013, the May 30 meeting of the Florida Building Commission’s Hurricane Research Advisory Committee (“HRAC”) has been temporarily postponed.
Yet pending on the HRAC agenda is a University of Florida (“UF”) presentation on post-storm damage assessments and ongoing research directed at discontinuous roofing systems. To view the presentation, click here.
Among the proposed tasks set forth in the UF presentation is a study of wind load resistance as it relates to asphalt shingle roof systems. According to UF researchers, recent studies suggest that the problem of asphalt roof shingles’ diminished adhesion performance over time may be readily solvable.
In these studies, significant roof shingle loss in high winds is prominent for roofs that have naturally aged six years or more, but not as prominent for newer roofs. UF researchers are currently finalizing technical papers of recent studies that have experimentally identified:
- A strong correlation between shingle vulnerability to wind and the pre-wind event condition of the sealant that attaches the underside of the leading edge of the shingle to the top of the course of shingles below it
- A large percentage of the existing aged roof inventory (also six years or more) have widespread occurrences of numerous unsealed shingles. The observed cohesive failure of the sealant indicates that these shingles were initially sealed upon installation and became unsealed as a result of natural aging.
Together, these findings strongly indicate that a major contributor to the failure of shingles in high winds is the loss of adhesion in the sealant over time, unrelated to a wind event. It has been clearly demonstrated that this loss of adhesion occurs in a much shorter time frame than the recommended 20-year replacement cycle of asphalt roofs.
The necessary component to seek a solution is the identification of the mechanisms that lead to the unsealed condition. A recently completed field study to identify unsealed shingles on 27 Florida homes led to the observation that a pattern of in situ (in position) unsealed shingles systematically coincides with the installation pattern.
UF researchers have hypothesized that the likely causation of age-related shingle unsealing is thermal cycling producing unevenly distributed stress concentrations in the sealant due to the shingle installation pattern. Now, they are proposing to investigate this hypothesis in a one-year performance period beginning July 1, 2013. The methodologies will include experimental and finite element analysis investigations of the stress concentrations in the sealant when the shingles are subjected to time-varying thermal loads. A consistent finding of higher stress and/or strain at the sealant on the tab that overlaps the end joint of the course below would confirm the causation hypothesis.
The proposed experimental work will be conducted using existing laboratory facilities, primarily the accelerated aging chamber that allows a controlled time varying heat, UV and water spray environment. Relative displacements between shingle courses and stresses at the adhesive interface will be monitored to identify regions of higher stress and/or strain concentrations.
Currently, UF is continuing its ongoing investigation into the susceptibility of tile roof systems to failure in hurricane winds and their windborne debris characteristics, along with potential impacts on surrounding housing. To view the project scope, click here.
The HRAC was started in 2005 by then-Florida Building Commission (“Commission”) Chairman Raul Rodriguez, who appointed the small coordinating group consisting of Commissioners and other stakeholder representatives. The group was charged with identifying research being conducted related to building failure issues resulting from the 2004-2005 hurricanes; identifying any research gaps on key issues identified, but not being researched; and finally, ensuring that the Commission is provided with all relevant research findings on each of the major issues, prior to the Commission considering code enhancements resulting from lessons learned.
The HRAC meets on an ongoing basis for the purpose of receiving updates on current research initiatives, providing recommendations on needed research projects and funding for same, and providing recommendations regarding proposed code amendments relevant to hurricane and storm protection and resistance enhancements.
Currently, the Commission is beginning rule development on its triennial statutory review of the Florida Building Code.
HRAC members are listed below:
- Dick Browdy, Chair; Florida Building Commission
- Joe Crum, Certified Building Official; Building Officials
- Jaime Gascon, Professional Engineer; Local Government
- Jack Glenn, Certified Building Official; Home Builders
- John Ingargiola– Federal Government (FEMA)
- Do Kim, Professional Engineer; Insurance Industry/Researchers
- Craig Parrion, Professional Engineer; Product Manufacturers (concrete products)
- Tim Reinhold, PhD, Professional Engineer; Insurance Industry/Researchers
- Richard Reynolds; Insurance Industry
- Jim Schock, Certified Building Official; Building Officials
- Chris Schulte; Roofing Contractors
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