Challenges Addressed
Listed on the National Register, the building’s exterior needed to remain as close to original conditions as viable. Designers were allowed to modify the main entry to align with the new office-space programming but—other than the northside lobby space—truck-loading docks lined the ground floor. Working in collaboration with the state of Illinois and National Historic Landmarks officials, the team created new entrance doors in the same size, shape and location as the former loading docks and added stairs and ADA ramps.
To match the historic paint color, they removed peeling paint chips from the building and examined the layers under a microscope. The team replaced more than 2,000 exterior windows with energy-efficient ones that mirror their historic counterparts right down to the mullions’ profile.
While vacant, a leaking roof and broken windows brought 20 years of moisture inside. “The engineers estimated between one and two Olympic-sized swimming pools of water had absorbed into the concrete,” Rogow says. “This was a significant problem because we weren’t sure how to make anything adhere to it.”
After resealing the building with a new roof and windows, the team used temporary HVAC equipment to pump very dry air into the building for more than a year while other construction activities were underway. Then, they replaced the building’s mechanical equipment and continued to run de-humidified air into the space until the concrete finally dried out.
The Old Main Post Office relied on rail service, and the building sits atop 18 active Metra and Amtrak train lines. Consequently, a smoke plenum exists below the first-floor slab. The plenum is a sheet-metal, steel-rod-hung, 3-foot-deep crawl space containing channels with fans that collect train exhaust, run it up through chimneys within the building and expel it outside.
“We didn’t have a basement to sink new escalator or elevator pits nor plumbing for food service on the first floor,” Rogow remarks, “so we built a 4-foot-high plinth out of structural steel, concrete and high-density foam that helped keep the platform light.”
Existing freight elevators were converted into passenger elevators and ADA ramps were added. New first-floor escalators transport occupants to the second floor, where the team added new elevators that rise into the upper 8 stories. A raised platform to house plumbing will also serve the future food hall. Despite the platforms, the double-height volume of the first floor—rising 37-feet tall in the lobby area—still offers an impressive sense of spaciousness.
Because trains still stop and idle beneath the building, the team located the public food hall on the north half of the first floor. When the food hall opens during a future construction phase, its lively atmosphere will make train vibrations less noticeable.
Initial plans for the post office organized the structure to allow a future highway to run directly through the main floor, but by the time Interstate 290 (known as the Eisenhower Expressway to locals) was constructed decades later, truck heights had increased. The building’s entire second floor had to be raised in 1955 to accommodate the plan, and a new concrete structure was added.
“To accommodate the non-contiguous first floor, we added escalators that allow tenants to walk in, then up and over an internal overpass. But if you didn’t know the highway was below you, you’d never guess it,” Rogow explains.