Rooted in Purpose
As part of the city approval process, the developers agreed to contribute significant public realm improvements, including a nearly one-acre waterfront park and a mid-block pedestrian plaza linking Vaughan and Green Streets. The plaza, though modest in size, and streetscape faced a classic urban design challenge: how to support healthy, mature trees within a hardscape.
Rather than settle for decorative planters or narrow tree pits, the project team embraced a progressive solution: Citygreen’s Stratavault™ soil cell system.
Engineering Life Below the Surface
The design called for a suspended pavement system - a layered installation where pavers sit atop a structural matrix, allowing uncompacted soil and healthy root zones to exist below. Within each tree zone, a matrix of modular Stratavault™ units was installed, filled with engineered soil, and capped with geotextile and surface paving.
This approach achieved multiple goals:
- Expanded available soil space for tree roots
- Preserved hardscape integrity for foot and vehicle traffic
- Prevented future root heave and infrastructure damage
- Enabled the trees to access oxygen, moisture, and nutrients at scale
Stratavault not only met the load-bearing requirements for the plaza and surrounding street trees but offered a vastly expanded root zone compared to conventional urban tree plantings, allowing the trees to thrive rather than merely survive.
A Model for Urban Tree Integration
For the City of Portsmouth, this plaza design supports long-term tree health, aligning with its goals for climate resilience, pedestrian connectivity, and increased canopy coverage in urban corridors. Where many cities have seen street trees fail prematurely due to soil compaction and lack of space, the AC Marriott Hotel plaza flips that script.
These trees are expected to mature into full-shade canopy providers, helping cool the hardscape, reduce the heat island effect, and create a welcoming environment between two anchor destinations: the hotel and 3S Artspace, a cultural venue next door. This project sets a new bar for how hotels and private developments can contribute to the public realm.
Connecting to the Bigger Picture
Importantly, this is not an isolated gesture. It is part of a larger livability vision - the North Mill Pond Greenway, a future waterfront park and trail network being developed on land donated by the hotel’s developers. Designed by Halvorson | Tighe & Bond Studio in partnership with Tighe & Bond Engineers and DeRosa Environmental, the greenway will create habitat restoration areas, bike paths, shade pavilions, and pedestrian lookouts along the pond’s edge.
