An Adventure in Excavation

If restoring a historic building is a challenge, restoring half of it and renovating the other half is a far more demanding and risky venture. When the American Enterprise Institute (AEI) bought 1785 Massachusetts Ave NW in Washington DC, a 60,000-sf National Historic Landmark building, it was 12,000 square feet too small for their needs. Its landmark status posed a problem for expansion, but Grunley Construction, an AGC of Metropolitan Washington D.C. member, suggested an innovative plan to increase usable space by constructing a penthouse on the top, and digging an entire second basement beneath the existing basement, adding 28,000 square feet in all. For this outstanding restoration/renovation, Grunley received the 2017 Alliant Build America Award for Building Renovation $10 to $99 Million.

Originally built as luxury apartments in 1917, the Beaux Arts-style structure was converted to office space during the 1940s. The layout of the building was unusual: 40 percent of each floor was a mezzanine level originally designed as servants’ quarters, set several feet higher than the rest of the floor.

As Grunley’s senior project manager Shawn Link explains, the terms of sale from the former owner (National Trust for Historic Preservation) "allowed an easement to make it more conducive to office space" by renovating the mezzanine portions of each floor, "but had a historic preservation easement for 60 percent of the building." The building’s exterior, too, had to retain its historic character.

To dig a new basement beneath the existing one, Grunley had to transfer structural load from the 29 interior steel columns supporting the structure, so they could excavate underneath them.

"This was a very challenging excavation," says Link, "even though 10,000 cubic yards isn’t all that much." It wasn’t the quantity of the work; it was the delicacy. For each column, they drove four micro-piles—essentially steel I-beams–into the ground, attached jack-brackets to the base of the column, and placed hydraulic jacks to lift each column and transfer its load to the micropiles. Since jacking the frame risked cracking the exterior façade or the interior plaster detail, movement and vibration monitoring equipment was installed. The columns were raised just 5/100" to transfer load. Then, Grunley dug beneath the columns, adding diagonal braces to shore the piles as they went. "There was a lot of hand-digging," recalls Link.

Grunley demolished the mezzanine floors completely, opening up almost half the building down to the basement level. They built new floor plates level with the remaining floors.

Grunley preserved the original staircase, wood flooring, ceilings, windows, and almost all of the walls and cornices. They also restored the historic limestone façade. At the same time, they added a modern heating and cooling system, plumbing, electrical and communications wiring, LED lighting, and an extensive audio/visual package with speakers concealed in the walls covered by a thin coat of plaster. The original plaster contained asbestos, so every cut in the walls had to be performed under hazardous materials containment.

The completed AEI headquarters, re-designated as 1789 Massachusetts Avenue, includes two kitchens, a servery, penthouse-level rooftop terrace, state-of-the-art video and audio production studios, auditorium, fitness center and Zumba studio, conference rooms, event and entertaining spaces, dining room, library, and custom pantries on every floor. All that, and a lot of history.

Associated General Contractors of America
2300 Wilson Blvd, Suite 300
Arlington, VA, USA
Ph: 703-548-3118 Fax: 703-837-5402