The 40,165-sq.-ft., five-story Spence School being constructed on 56 E. 93rd St. on Manhattan's Upper East Side was really three projects in one - a renovation/historical preservation, underground construction and an expansion.

Construction on the approximately $30 million project began in January 2002. "The main challenge was fitting their program into the existing building envelope," said Jim Sager, senior associate with Platt Byard Dovell White Architects, the project's New York-based architect.

The existing building was originally a four-story private residential mansion that was constructed in the 1930s. In the early 1970s, Roosevelt Hospital took over the building and turned it into a drug rehabilitation center.

It was also a landmark building, which meant that exterior modifications had to be kept to an absolute minimum. "It was primarily program-driven and we had a limited amount of space to work," Sager said. The program - what the school needed and wanted for its growth - consisted of building a gym, library, 15 classrooms and spaces for music, art, dance, science labs and a computer lab.

To get what the school needed, Sager had to go up - and down.

Underground Gym
The gym became the underground element of the construction. Because the gym was in the program, and the existing building did not have the capacity for it, there was only one way to go: down.

To construct the gym, crews pounded 35 ft. deep into rock with hydraulic hammers.

Removing the rock was difficult because only one lane of traffic was closed on 95th Street. "To remove the excavation materials, a hole was dug in the sidewalk and the materials were pushed to the hole and lifted out," Sager said.

"The excavation took one year," added Robert Trostle, senior project manager for F.J. Sciame Construction Co. Inc., the project's New York-based construction manager.

The excavation and foundation construction was a separate bid package. Trostle said that the project was broken up into two phases so workers could get an early start. The first was the excavation and foundation work and all work up to the underside of the second floor.

The second phase was all the work from the second floor to the new fifth floor, which consisted of restructuring the existing building, interiors and adding a fifth floor.

Noise and fumes presented problems to many in the primarily residential neighborhood during excavation. The solution was to shift work hours from 7 a.m. to 6 p.m., to 8 a.m. to 5 p.m. shift work hours.

"Now that the building is semi-enclosed, the noise and dust has been minimized," Trostle said.

The foundation work consisted of 12-in.-thick, cast-in-place concrete walls with heavy steel rebar that was built after shoring up the foundations of the surrounding buildings. In addition, the north end of the excavation required some shoring of the existing building.

"Caissons were drilled underneath the rock to seat the building," Sager said.

Also supporting the building will be a large steel truss that is 12 ft. deep and 80 ft. long that spans property lines and runs down the center of the gymnasium. "The truss had to be built onsite because it was too big to transport whole," Trostle said.

Sager added, "The truss was able to eliminate some additional shoring to the building because the contractor had an idea to integrate some of the columns into the truss."

Tying In
Tying in the new elements into the structure make up the project's second and third elements - a historic preservation/renovation and expansion.

Structurally, the exiting building was steel frame and limestone, but the framing system had to be overhauled. To thread the new steel into the old building, Trostle said: "We had to remove the main structural column - after shoring - then placed a new column and tied in with new beams. This was done throughout the entire structure."

To thread the new steel members, holes were chopped into the floor and then the affected beams would be shored up. Additionally, a new flooring system was installed that consists of concrete with a metal deck.
Although the exterior could not be altered significantly, the windows could be replaced by Thermopan units with a profile that matched the existing façade profile. "Working with the landmark, we made calculated additions to the exterior," Sager said.

However, not much of the exterior changed. "The existing slate roof was carefully removed and reused as well as existing limestone chimneys," Trostle added.

In the interior, many elements were carefully restored, including the wooden molding, and existing plaster details were molded so that they can be recast.

"There were a series of existing spaces that we identified as the heart and soul of the interior and we tried to preserve them, like the lobby," Sager said. "Our intent was to preserve the space and transition to a more modern vocabulary."

That modern vocabulary is the fifth floor, which is set back from the original building and will be enclosed by a new material called a turncoated stainless steel panel system.

"We chose that material to be sympathetic to the original structure, but we wanted something a little different," Sager said.

Construction is currently on schedule and is expected to be completed by July.