Instead of leveling the site, the developer, RMR Group, decided to reuse and repurpose the structural skeleton to give the project a head start toward reducing its overall carbon footprint by more than 50%. Image courtesy Leo A Daly
Overshadowed by neighboring Union Station and the nearby U.S. Capitol, the seven-story largely precast-clad structure at 20 Massachusetts Ave. NW in Washington, D.C., likely has been perceived as just another office building occupied by a government agency. And indeed it was for most of its 50-year life. That perception will soon change with the scheduled spring 2023 completion of the building’s $200-million transformation into 20 Mass, a 425,433-sq-ft mixed-use development that will combine Class A office space with a 274-key Royal Sonesta Hotel and ground-floor retail. Stone Tile
The building will be expanded by more than 101,000 sq ft by the addition of three floors and a full-height eastward expansion, and clad with a new unitized curtain wall exterior. It will feature amenities such as a 15,508-sq-ft penthouse level with a green roof, a fully equipped fitness club with private lockers, a secured bike room and restaurants. According to architect Leo A Daly, a streetscape redesign will transform the building’s visual and experiential relationship to the Massachusetts Avenue corridor and surrounding streets.
The project includes a streetscape redesign that will transform the building’s visual and experiential relationship to the Massachusetts Avenue corridor and surrounding streets. Image courtesy Leo A Daly
It’s doubtful that many people would have missed the existing building had Newton, Mass.-based developer The RMR Group elected to level the site and start from scratch. But RMR senior project manager Chris Chartier Cotter says the strategy has always centered on renovation, as reusing and repurposing the structural skeleton would give the project a head start toward reducing its overall carbon footprint by more than 50% and meeting its goals of attaining LEED Gold and WELL Silver certifications.
Leo A Daly project architect Andrew Graham says the theme of reuse and repurposing “had a ripple effect through a lot of coordination decisions we had to make through a lot of different disciplines.” That included being locked into the existing cast-in-place construction and floor-to-floor heights while at the same time incorporating the right mix of office and hotel amenities.
“It set the stage for the challenges we had as designers,” Graham says.
That includes the building’s unusual trapezoidal shape, which had limited the amount of natural light to the interior. Leo A Daly design principal Irena Savakova says the team turned the challenge into an opportunity with a plan to cut out large sections of floor plates to create atriums—one full height and another rising three stories in the hotel area. Reducing the depth along all building sides, Savakova explains, “gave us the right allocation of space on all sides and at the same time created a more wellness-promoting interior environment.”
Cotter agrees, adding that while the approach added to the project’s many technical challenges, “we would be able to set up the building in a much better way for tenant demand and support the way they operate.”
The building’s lobby is designed to allow the public to cut through the building instead of having to walk around it. Image courtesy Leo A Daly
Executing this strategy required approximately a year of preconstruction activity with DPR Construction before the contractor mobilized field crews in June 2021. DPR project manager Kurt Sandberg says the tight site offered little in the way of laydown space, with the added constraint of a small, yet historic building just 40 ft to the east.
Although the two-level underground parking garage provided limited room for material storage, Sandberg adds, “We had to coach the trades on being lean and using just-in-time deliveries.”
Erecting two tower cranes to cover the entire site, DPR crews gutted the building by first removing the exterior precast panels and working their way inside. The process generated more than 10,000 lb of concrete and other material, nearly three-quarters of which was recycled. Along the way, workers uncovered extensive undocumented asbestos, a discovery that required frequent schedule adjustments as demolition and abatement subcontractors mobilized additional crews to work on multiple floors.
The building had limited natural light due to its trapezoidal shape. The team solved the problem by cutting out large sections of floor plates to create atriums—one full height and another rising three stories in the hotel area. Image courtesy Leo A Daly
Those weren’t the only surprises the project team would encounter. As Cotter notes, “As-builts don’t always live up to their name.”
For example, DPR laser-scanned the interior and found that the floors needed far more leveling than anticipated. Nor did column grids match up with the original drawings. “We had to go through a lot of gymnastics with the design team and trades on how best to adapt to what was there,” Sandberg says.
To prepare the structure for the additional floors and large atrium cutouts, DPR jacketed lower columns with rebar surrounded with 4 in. of 6,000-psi self-consolidating concrete. Seven 8-in.- to 12-in.-thick shear walls were also added, along with eleven 41-ft-deep micropiles installed below the garage’s slab-on-grade to support relocated stair towers and elevators. Concrete saws and remote-controlled demolition machines then went to work on the 8-in.-thick floor and roof slabs, cutting 2,400-sq-ft sections for the full-height atrium and 1,250-sq-ft sections for the three-level hotel atrium.
DPR also began the upward expansion of 20 Mass with new 7-in.- to 11-in.-thick post-tensioned floors and roof slab and supported the east side extension with eleven 80-ft-deep micropiles. Once again, there were surprises—from a previously unknown rooftop electrical feed that had to be decommissioned to the discovery of brick foundation remnants and contaminated soil suspected to have been left over from long-ago demolished rowhouses. “We had to do a lot of work-arounds, but everyone worked together,” Sandberg says.
A worker prepares an existing column for jacketing with rebar and an additional 4 in. of concrete. Image courtesy Leo A Daly
Although the availability of more detailed information about the building’s existing condition might have helped avert at least some of the schedule scrambling, supply chain hiccups have been more problematic, affecting elements as diverse as skylight glass, bathroom tiles and electrical panels.
One facet where the project team managed to stay ahead of supply chain issues was the unitized curtain wall. Pioneer Cladding and Glazing Systems Inc. of Cincinnati was enlisted early as design-assist partner.
One of three new MEP chases rises more than 98 ft through the center of 20 Mass. It houses plumbing risers and commercial-kitchen exhaust ducts. Image courtesy Leo A Daly
Design team architects made frequent visits to Pioneer’s fabrication plants to ensure the approximately 2,000 5-ft by 10-ft, 800-lb curtain wall components captured the design concept of a pronounced base, a middle and a top, according to Leo A Daly. The curtain wall system is strategically articulated and recessed along different floors and facades and incorporates unitized terra cotta, deep aluminum fins and vision and spandrel glass.
Prefabricated hotel room bathroom pods and exterior wall panels facing a public alley helped the project team regain time, Sandberg says, as have a variety of project management software tools for scheduling deliveries, trade use of the tower cranes and material hoist and other activities.
“Our ability to self-perform concrete and drywall helped, too,” he adds. “Using our own crews enabled us to hop around and adjust manpower more easily as issues arose.”
A canopy at the hotel cantilevers approximately 20 ft and is supported on the interior of the building with structural framing tied back to jacketed concrete columns.
Leo A Daly’s Graham says the project has offered some valuable lessons in collaboration as well, particularly because it spanned a pandemic that introduced uncertainty into nearly every aspect of the design and construction process.
“Keep an open mind with your client and construction team on how you can leverage the expertise to tackle issues that are there,” he advises. “As challenges arose, all of us have worked together to solve them.”
RNR’s Cotter likewise praises the collaborative effort to mitigate issues that might have delayed progress, adding, “We’re excited to see this project come to life.”
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