1789 Massachusetts Avenue Northwest

Located near Dupont Circle, 1789 Massachusetts Avenue NW is a national historic landmark built in 1917. It originally served as a luxury apartment building and home to Andrew Mellon, a wealthy financier, philanthropist and politician. In 2013, the National Trust for Historic Preservation sold the five-story building to the American Enterprise Institute for Public Policy Research, a think tank that would occupy the property as its new headquarters after a $40 million renovation.

The ambitious project scope involved the excavation, underpinning and construction of a new 28,000-square-foot level below the existing basement, construction of a new central core, and reinforcement of the steel structure to accommodate the addition of a penthouse with balcony views of the neighborhood.

SEDC was responsible for the subsurface investigation, consisting of obtaining drilling permits, drilling borings, excavation of two interior test pits, and preparation of a geotechnical report. Along with new spread footings, we also recommended underpinning with traditional hand-dug piers and with micropiles. This solution supported existing structural elements while preserving the physical character of the historic building.

During construction, SEDC provided full-time construction inspection and materials testing, to observe the proper installation of the improved foundation system, earthwork, sub-drainage system, and waterproofing.