Let there be light: Union Station Great Hall

Originally completed in 1925, Chicago’s Union Station was designated a landmark in 2002 and listed by AIA Illinois as one of the 200 Illinois Great Places. The restoration of the station’s Great Hall sought to maximize the reuse of existing materials and infrastructure, preserve the historic integrity of prior generations, and significantly reduce its energy use.

The project team, led by local architecture firm Goettsch Partners, was brought in to investigate and assess the existing conditions of the 219-foot-long vaulted skylight, and to design and construct a new watertight skylight over the original system, while fully restoring the deteriorative finishes. Previous patch repairs to the leaking skylight altered its appearance and decreased the amount of natural light in the space.

The new, energy-efficient skylight, built five feet above the original cast-iron skylight, is comprised of 858 panes of clear, high-efficiency glass that protects the building while brightening the Great Hall interiors with 50% more daylight than before. Another 2,052 pieces of glass in the existing skylight were replaced.

An energy analysis conducted before work began evaluated the potential impact of the new skylight in conjunction with the existing skylight by creating a 3D model of the existing Great Hall conditions to use as a baseline for simulating different design scenarios. Critical variables were investigated: the annual heating energy, the temperature of the volume of space between the existing and new skylights, the solar heat gain into the Great Hall, and the heat conduction of the new skylight.

Annual heating energy results showed a 13% savings through the combination of replacing the existing monolithic skylight with double glazing, cutting solar heat gain by up to 29% annually, and a 67% savings in heat conduction due to improvements in thermal resistance and the reduction of outdoor air infiltration.

Historic lighting fixtures were restored, rewired, and upgraded to dimmable LED. Surface-mounted cornice lights were replaced with asymmetrical reflector LED fixtures. A control system was then connected to a dimming day/night scene selection with daylight sensor controls to reduce lighting intensity when necessary. This resulted in a 60% reduction in wattage from 1.9 watts/sf to 0.76 watts/sf.

Union Station is the third-busiest metropolitan transportation station in the country, hosting 35 million Metra passengers annually, so it was imperative for the building to remain open with minimal disruptions during the restorative work. A unique 24,000-sf work deck was created and hung from the skylight girders, eliminating scaffolding that would have taken up valuable space on the floor. From this work deck, installation of the new skylight, restoration of the historic skylight, and restoration of the ornamental plaster and historic lighting were completed, all while 130,000 daily commuters passed by directly below.

SILVER AWARD WINNER

BUILDING TEAM Goettsch Partners (submitting firm, architect) Amtrak (owner) Klein & Hoffman (SE) ESD (MEP) Berglund Construction (GC) DETAILS 600,000 sf Total cost $22 million Construction time August 2015 to January 2019 Delivery method Design-bid-build