The roof of the new Seahawks Stadium and Exhibition Center in Seattle, WA was designed to make a statement. The roof design resembles two partially opened clamshells facing each other. According to Kelly Kerns, project leader for Ellerbe Becket Architects of Kansas City, the roof and the arch itself are two of the most defining points in the design.
Accordingly, a soft white Johns Manville UltraGard® PVC membrane was selected for these two high profile areas of the roof. "We wanted a roof that would read well against the skyline," Kerns said.
The highly exposed, large high roof surface presented a number of challenges for the roofing contractor, Queen City Sheet Metal and Roofing, Seattle, WA. The 200,000 square foot roof is 200 feet high. This height coupled with the wind, made material loading difficult. But even more challenging was the fact that the roof had to meet an FM 1-90 rating. The greatest concern was wind uplift and pressure from the topside with such a large roof surface that is exposed on both the under and topsides.
"We put 22 half sheets around the perimeter to prevent wind uplift," said Robert Rhodes, vice president and operations manager for Queen City.
The PVC was mechanically attached to a metal deck. Flashing a 1200-foot gutter at the bottom of the clamshell proved to be challenging. Queen City used an 80-mil JM UltraGard PVC membrane for flashing and tied it in with metal. Custom-made expansion details were required for the huge supporting beams that came through the roof.
There were a number of other unique details on the project. Rhodes credited Tom Vicario, the Johns Manville technical representative, for recommending that the interior flashings were put together with the termination bars. He also recommended clad metal details and a cricket design to keep water moving direct to the drains.