Restoring Chicago's Union Station Skylight

CHICAGO's Union Station is the fourth busiest rail terminal in the United States - handling about 140,000 passengers a day - and is one of the city's most iconic pieces of civic architecture. 

Built in 1925, the station's vast "Great Hall" is topped by an expansive 18,000 square foot (1,670 square metre) skylight, originally built using cast iron members and glass panes sealed with an oil-based sealant.

Above: The skylight of Chicago's Union Station hasn't been thoroughly renovated since the station opened in 1925 (image courtesy of EarthCam).

As the sealant began to dry, the roof began leaking, a problem that has been documented since the 1930s.

The structure has only ever had sporadic maintenance ever since and was even completely blacked-out using tar during the Second World War.

Above: The renovations took place without disrupting the passengers (image courtesy of EarthCam).

By 2015, leaks had started to damage the plasterwork inside, and Amtrak, the owner of the Chicago Union Station, decided it was time to renovate the Great Hall, along with the skylight.

Above: A secondary skylight has been constructed around the original structure to keep out rain and improve thermal performance ( image courtesy of EarthCam).

Chicago architecture firm Goettsch Partners was asked to come up with a solution.

The resulting project consisted of restoring the historical skylight, which consists of 2,052 panes of glass, to its original appearance and encasing it in another modern, fully glazed, skylight about 5 feet (1.5 metres) above the original structure.

Above: A scaffolding platform for the workers was suspended from the original structure (image courtesy of EarthCam).

In order to minimise the disruption in the Great Hall, the scaffolding was suspended from the skylight's arches rather than standing on the floor.

Once the skylight restoration was complete, original decorations inside, damaged by years of leaks, could also be brought back to their original condition.

Above: The new skylight lets in 50% more light than before the renovation (image courtesy of EarthCam).

Costing a total of USD $22 million, the project has stopped the leaks and provided better protection against Chicago's extreme climate.

Another benefit is that 50% more natural light is able to enter the Grand Hall thanks to the modern construction.