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How does an air-supported stadium roof stay inflated?

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Michigan Stadium, Ann Arbor — Stadium Aerial view of Michigan Stadium, home to the gridiron football team of the University of Michigan, Ann Arbor.

An air-supported stadium roof is a type of pneumatic structure that maintains its shape through internal air pressure. The process works as follows:

Internal Pressure: The air pressure inside the stadium is increased to a level slightly above normal atmospheric pressure—often by as little as 1.5 percent—using fans or compressors. This pressure pushes upward against the fabric membrane, keeping it taut and allowing it to resist exterior wind pressure.12
Structural Support: The membrane is typically restrained by a network of steel cables attached to a rigid compression ring at the perimeter of the stadium. These cables serve to stiffen the fabric, preventing it from fluttering under uneven wind loads and providing structural support in the event of accidental deflation.123
Operational Requirements: Because the interior must remain pressurized, air locks are required at all entrances to prevent the loss of internal air pressure when people enter or exit the building.1

This design is considered one of the most cost-effective methods for covering very long spans, as seen in stadiums like the former Hubert H. Humphrey Metrodome.13