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Vacuum Uplift Forensic Testing To Determine if Hail-Caused Dents Substantially Weakened the Membrane Bond

Industry

Education

Location

Colorado

Services Involved

Forensic Testing

Year

2024

Experts Involved

Steven R. Smith, PE

The Problem

  • A hailstorm struck an educational facility in Colorado with an adhered, single-ply thermoplastic polyolefin (TPO) roofing membrane spanning approximately 154,000 square feet.
  • The TPO membrane showed no visible signs of fracturing or surface rupture. However, stakeholders voiced concern that the impact from hailstones may have compromised the bond between the membrane and its substrate, weakening the roof’s resistance to wind uplift and affecting long-term durability.
  • Due to the scale of the roof and the potential implications for repairs, the school required a reliable, scientific evaluation of membrane performance post-event.
Roof open after failure

The Solution

The Haag forensic team, with the leadership of Steven R. Smith, PE, mobilized quickly to assess the roofing system’s condition through vacuum uplift testing.

  • We calculated the design wind uplift pressures for the roofing system in accordance with local building codes and industry standards.
  • Multiple test sites across different roof sections were selected to ensure comprehensive sampling and accurate data.
  • Our technicians placed a vacuum chamber securely over the membrane at each location. They incrementally raised vacuum levels to simulate increasing wind uplift pressures, all corresponding to the thresholds outlined in Factory Mutual Datasheet 1-52.
  • The team measured membrane deflections beneath the dome to learn how the roofing system responded under simulated wind loads during each test.
  • After the pressure-based testing phase, Haag conducted multiple roof cuts, including one in a location where uplift failure occurred, to inspect the internal assembly, pinpoint causes of failures, and demonstrate the effects of hailstones on membrane adhesion.
Vacuum dome placed in corner

The Outcome

In summary, hailstone impacts caused localized delaminations between the membrane and the uppermost insulation; however, only one location on the roof failed to withstand test pressures.

Examination of the roof assembly at the failed test region revealed the weakest link in the system was the adhesive bond between insulation boards, rather than the membrane itself.

Consequently, if the property is subjected to an extreme wind event, the roof would likely fail due to separation between insulation boards before uplift pressures reach levels sufficient to peel away the membrane.

Steven R. Smith, PE

Expert Highlight

Steven R. Smith, PE

Steven R. Smith, PE, Director of Research & Testing and a Forensic Engineer at Haag, played a critical role in guaranteeing the accuracy and credibility of this investigation. Since joining Haag over 24 years ago, he has led countless projects involving roofing system performance, material failure analysis, and forensic testing.

His deep understanding of thermoplastic membranes, adhesive systems, and vacuum uplift testing protocols enabled his team to diagnose issues quickly and accurately. Every phase of the investigation met the highest standards of technical precision.

 

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