What Do We Learn from Wind Uplift Tests of Roof Systems?

Abstract

There are several industry-accepted test protocols to evaluate the wind uplift resistance of commercial roofing systems (ASTM E1592, UL1897, UL580, FM 4470 etc.). These tests apply pneumatic pressure to full-scale roof specimens installed on a pressure chamber, and increasing the pressure until failure. The wind uplift design pressure is then determined by reducing the peak pressure by an accepted factor of safety (e.g. 1.5 or 2.0). A critical question to be asked on the results is the meaning or validity of these static test results when hurricane winds produce dynamic roof pressures that are constantly fluctuating in time and space? The presenter reviews similarities and limitations of common wind uplift test methods for standing seam metal panels, and mechanically attached single ply roofing systems that have been the industry-standard for many years and reports on research results for these systems. Most of the test protocols provide comparative results, absent any verifiable relationship to roof performance in actual wind storms. Of particular interest now is the determination of the wind design pressure for lightframed wood roof systems, for which there exists no industry-accepted test protocol. The fastener schedules and minimum fasteners included in current ICC building code today appear to be based on research conducted immediately after Hurricane Andrew. Recent experimental studies at the University of Florida revisited those studies and developed a new dynamic test protocol for wind uplift testing of roof sheathing panels. The results have shown inconsistency in previous tests and that static pressure testing of wood roofs may over-estimate their failure capacity when compared with dynamic pressure test methods. The presentation concludes with a proposal for standardizing the wind uplift testing of wood roof systems based on dynamic pressure fluctuations. The conclusion has far-reaching implications as similar modifications may be required to calibrate current static pressure test methodologies for commercial roof systems so that they for hurricane-prone locations.