By Barb Ernster
The air-supported membrane for the Mall of America Field at the Hubert H. Humphrey Metrodome sports stadium in Minneapolis held up impressively through Minnesota’s harsh winters, but in 2010—after 28 years—a record-breaking heavy, wet snow caused the membrane to tear and deflate. It was replaced in 2011 with the same St. Gobain SHEERFILL® PTFE-coated fiberglass, which still meets the building codes for fire retardancy, strength and endurance. But significant advances in tension membrane engineering have improved the function of the new roof in this climate.
With current software technology, the new membrane is patterned so the panels are flatter and the valleys between the panels are shallower. This allows snow to be scoured off the roof rather than accumulate in the valleys, as well as limiting the sloughing of heavy, wet snow into the valleys where it cannot be removed fast enough. Birdair Inc., Amherst, N.Y., detailed and fabricated the original roof as well as the new one.
With the removal of the inner liner from 40 percent of the center part of the dome, the “new” dome has a bright and airy atmosphere inside that is remarkably different, says David Campbell of Geiger Engineers, Suffern, N.Y. Experience with a similar design for the Carrier Dome in Syracuse, N.Y., taught engineers that eliminating the center panels actually increases snowmelt air flow to the center section and the overall effect is a net increase in the heat transfer to the snow through the roof.
Even with this positive effect, Campbell says air-supported roofs in general are not good examples of energy efficiency in colder climates. “They best serve as an example of something that has been done to save significant dollars in construction, but as a result they don’t respond to these northern climates. They don’t carry the snowload; you have to melt it, and they’re not thermally insulated, so you lose heat.”