Boston City Hall Square
Boston
BEST PROJECT
Sent by: Shawmut design and construction
Owner: City of Boston
Principal Design Firm/Civil Engineer: Sasaki
General contractor: Shawmut design and construction
MEP Engineer: Arup
Structural engineers: Weston and Sampson; SGH
Owner’s representative: Skanska USA
Spanning seven hectares, the $70 million comprehensive renovation has revitalized an iconic public space into a vibrant, accessible and sustainable urban square. The transformed space offers a variety of seating options, a public art space, a speaker’s podium, interactive water features, a children’s playground and other interactive elements that encourage social interaction and community participation.
To accommodate a 26-foot vertical elevation change across the plaza, the project team worked closely with the Boston Commission on Disabilities to create Hanover Promenade, a gently sloping central walkway that ensures access universal in all program areas.
Photo courtesy of Shawmut Design and Construction
Sustainability is at the heart of this renovation. Where the original impervious surfaces contributed to the neighborhood’s stormwater runoff problems, the combination of planting beds, permeable pavement, rain gardens and other green infrastructure filters 60% of the plaza’s stormwater and restores groundwater conditions.
Most of the rainwater from other parts of the plaza is collected in a 10,000-gallon tank for reuse as irrigation. Solar panels installed on site support the square’s energy needs, reflecting Boston’s commitment to renewable energy.
Photo courtesy of Shawmut Design and Construction
More than 250 trees, 3,000 shrubs and 10,000 new perennials and grasses shade more than half of the new square. In addition to creating a plant-rich environment that supports the local ecology, the extensive vegetation minimizes the heat island effect and sequestered more than 55,000 tons of carbon emissions.
A key challenge for the project team was the presence of three subway tunnels and associated ventilation structures beneath the plaza. Built in 1898, the tunnels did not have a nominal load. To mitigate the risk of differential settlements under new loads, detailed inspections and structural assessments were conducted to identify and repair compromised columns.
Photo courtesy of Shawmut Design and Construction
The team also overexcavated soil above the tunnels and installed lightweight fill materials such as geofoam and foam glass aggregate. This innovative approach ensures the long-term stability of both the plaza and the underlying infrastructure, reducing the project duration by more than six months.
The renovated plaza now serves as a dynamic civic space, hosting a wide range of public events from farmers’ markets to concerts and cultural festivals, setting a new standard for sustainable, inclusive and resilient public design.
