Laminated glass strength and clarity reach new heights at Skydeck Chicago

In July 2009, the Skydeck Chicago at the Willis Tower opened a new visitor attraction called “The Ledge” offering birds-eye views and heart-pounding thrills from an earth-defying glass cube 103 stories up in the air.


Photos: by courtesy of Skydeck Chicago at Willis Tower
Photos: by courtesy of Skydeck Chicago at Willis Tower

Extra-clear glass flooring uses tempered, low-iron glass and SentryGlas® ionoplast interlayers
At 442 m (1450 ft) tall, the Willis Tower (formerly Sears Tower) in Chicago is the tallest building in the Western Hemisphere. Now it gets a further distinction as host of a 103-story-high, all-glass visitor attraction called “The Ledge” where adventurers can step out into the sky for a heart-pounding view of an ant-like streetscape nearly a quarter mile below.

The Ledge is part of the already well-visited Skydeck at the Willis Tower. Since The Ledge opened in July, thousands of people have enjoyed the thrill-seeking experience each day. Visitors can enjoy the experience safely because it was constructed to bear five tons of weight.

The Ledge consists of two separate boxes jutting a little more than 1,2 m (4 ft) out past the edge of the Skydeck façade, creating a gravity-defying view that’s sure to thrill those who dare step out onto the glass floor. Strength of the all-glass construction comes from laminated glass, a multilayered sandwich of glass and clear adhesive interlayer sheet material that holds the layers of glass together. The laminated glass is assembled using minimally obtrusive framing, with bolts through the glass holding it to a retractable structural rail.

Stiff, tough, clear interlayer adds to glass floor safety and strength
The crystal-clear, see-through floors for The Ledge are made with 1,52 mm (60 mil) SentryGlas® interlayers sandwiched between three half-inch plates of fully tempered low-iron glass, a combination that’s unmatched for strength and clarity. Compared with traditional interlayers, SentryGlas® is five times tougher and up to 100 times stiffer, making it an ideal choice for improved structural performance in applications such as flooring, balustrades, building facades and security glazing.


Learn more about the The Ledge Project by downloading the case study: