“This is my end-all and be-all building,” said Zierer, who earned his architecture degree in 2012. “You’re still in shock because there are only a few in the world you can work on.”

Over the decades, many of Sullivan’s dozens of buildings have been demolished, including the St. Nicholas Hotel, which opened in 1894 a block from the Union Trust. Renamed and drastically remodeled in 1905, the St. Nicholas was razed in 1974. The Old Post Office Plaza occupies the site now.

Except for some alterations in 1924, the Union Trust’s exterior is original. Still in place are Sullivan’s elaborate terra cotta trim and cornice, arched windows, upper-floor columns and terra cotta lion heads. Removed during the remodeling were 15-foot gargoyles and large round windows on the second floor. The square windows that replaced the round ones will remain but the building’s current arched entrance will be reworked to resemble the rectangular entrance of 1924.

The National Park Service, which decides what may be done to National Register buildings and still qualify for federal historic preservation tax credits, rejected Gill’s request to reproduce the gargoyles. None exists as a model and old photos fail to show enough details to allow installation of reproductions, Gill said the park service ruled.