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Sears Tower to be reglazed using Butacite^®

Laminated glass with DuPont Butacite^® PVB interlayer saves energy as it beautifies the Sears Tower

Chicago's Sears Tower is an exceedingly buff member of the tall building pantheon. Should you linger at the base of 233 South Wacker Drive and crane your neck to appreciate the soaring form, you will be impressed.

It rises 1,454 vertical feet - 1,707 feet including antennas - and has the highest occupied floor and loftiest rooftop of any building on the planet. Viewing deck visitors gaze at sizable chunks of America's real estate - Indiana, Illinois, Michigan and Wisconsin - and on overcast days, the tops of swirling clouds.

But the true wow factor hits when one considers operating the Sears Tower. The interior sports 25,000 miles of plumbing, 2,000 miles of electrical cable and enough telephone wire to encircle the globe nearly twice. Its 104 elevators are among the speediest in existence, climbing at 1,600 feet per minute. And tuning the environment of the Sears Tower - or any skyscraper, for that matter - for occupant comfort is a precise science.

"We educate tenants that tall buildings do move in the wind," says Michael Flynn, partner at the eminent New York architectural firm Pei, Cobb, Freed and Partners. "People can detect very low levels of motions, but the buildings are designed to withstand the force of wind. In a windy city like Chicago, one could expect to feel motion in a skyscraper more in the winter season and perhaps several times a year in all." For the Sears Tower, average sway is six inches from center, though the edifice can accommodate 12 inches.

Keeping extremely tall buildings at a comfortable temperature demands rigorous attention, as well. "In the United States, tall buildings usually must be air conditioned until the outside temperature falls to freezing," explains Flynn. "The combined heat load of occupants, lights, computers and other equipment is frequently more than the building can lose unassisted even if it's cold outside. When computers were rare, lights generated most of the heat. Now we have efficient lights but more electronics, so the same heat issues apply today as 10 years ago.

"One of the most interesting developments in the high rise industry currently is energy-efficient window glass," he continues. "Companies already are formulating this type of glass. Unlike the old energy-efficient panels, it doesn't block out a lot of visible light."

Nice segue, Mr. Flynn. These days, the Sears Tower is approaching air conditioning needs and occupant comfort from that very angle.

TrizecHahn Corporation recently began replacing the building's 16,000 windows with energy-efficient laminated safety glass made with DuPont™ Butacite^® polyvinyl butyral interlayer. Overnight crews toil on the massive job from 6 p.m. to 6 a.m. to avoid tenant disruption. Projected completion date for the project is late 2007.

Laminated glass, formed by bonding two glass panes to a plastic interlayer, has been a standard for automotive windshields for 60 years. Used extensively in Europe and Australia for architectural applications, it is found commonly in the United States on horizontal or slanted roofs. With this installation, Sears Tower is showcasing the myriad possibilities of laminated glass to the North American building industry.

The Sears Tower project was recently on the cover of DuPont Magazine

The laminated glass fabricator on the job, Minnesota-based Viracon, coated the Sears Tower bronze glass panels with Viracon Solarscreen® cinnamon reflective coating. It reduces glare and possesses a shading coefficient that significantly lowers solar heat gain.

"Cooling costs are much lower with this window system," reports Joe Marks, vice president, sales and marketing for Viracon. "It also eliminates large temperature differences between exterior and interior offices." Energy use reduction has helped the building owner meet goals under the new Energy Star Building Label Program with the U.S. Environmental Protection Agency and the Department of Energy.

"Laminated glass with Butacite® absorbs 99 percent of the ultraviolet rays, and this helps protect carpet and furniture from fading," says Jeff Granato, DuPont architectural marketing manager. "But it also reduces the need for artificial lighting by letting lots of visible light - and fabulous views of the skyline - into the work environment."

Architects are extending the utility of laminated glass beyond its environmental attributes. It effectively attenuates external sound, making it especially welcome in large cities like Chicago that tend to be noisy.

The excellent safety profile of laminated glass has been recognized for years outside the United States. The material distinguishes itself when compared with typical safety glass. Challenged by collisions and weather extremes, laminated glass stays in the opening. If broken, the pieces adhere to the inner layer, providing a safety net for tenants inside and passersby below. This quality also provides excellent security at street level by deterring thieves and vandals.

It's no wonder laminated glass is glazing the globe's most prominent buildings, including the newest challenger for the title of world's tallest in sheer height: the Petronas Towers in Kuala Lumpur, Malaysia. The award-winning architects of the dual sensation chose laminated safety glass with Butacite® to meet progressive building codes in that country.

"Architects are turning more and more to glass," summarizes Granato. "They are letting in the outdoors with it and even incorporating it as a structural build- ing element. We at DuPont are changing the view that glass is fragile and that we have to live with that hazard in order to enjoy its benefits."

By replacing the 16,000 windows of the Sears Tower, building cooling costs will be slashed, exterior noise dampened, and carpet and furniture protected against fading.