A winning green roof

Toronto City Hall Podium Roof Garden – the first phase of the Nathan Phillips Square Revitalization Project, and the country’s largest accessible green roof – has won a CSLA (Canadian Society of Landscape Architects) Regional HONOUR Award. Kudos to the designers: the Toronto-based firms of Plant Architect and Shore Tilbe Irwin & Partners.

The podium roof of City Hall is at once part of the raised walkway system and the largest and most secluded of the Square’s perimeter gardens. The new green roof consists of three formal conditions: a sedum mosaic, a paved courtyard that frames the curved chamber and a deck café that occupies the prow. The perimeter garden is treated as a field in purple, pink, yellow/orange and green sedums. This ground cover is planted in a prevegetated tray system with shade tolerant species concentrated in the shadows of the City Hall’s towers.

The edge of the podium roof is lined in a walkway paved in precast planks, flush with the planting trays and interlocking with them. Wood benches complete the field, distributed around the roof in the planting beds. In future, a demountable kiosk will allow the prow to be programmed as a fair weather bar/café overlooking the Square. The council chamber floats on a disk of granite chip pavers, which acts as a site for events and temporary art installations. This courtyard is lit with a dispersed pattern of light columns, and the sedum field is illuminated by lights recessed in the roof-edge guardrail, creating the effect of a glowing garden when seen from adjoining buildings.

The podium roof is connected to the Square by the ceremonial ramp at the south, repaved and with a lit wooden rail along one side. It links to the elevated walkway by a stair at its Eastern edge, to Hagerman Street in the North, and to the lobby and council chamber of city hall through elevators within the existing building.