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June 3, 2010

Toronto City Hall gets a green roof




For 15 years, a police barricade at the bottom of the ramp to the right of City Hall’s front door has blocked access to the vast roof that surrounds the council chamber. Last Friday, the barrier came down.Mayor David Miller, flanked by architects, school children and a band, will lead a throng up to the city’s new green roof, as part of the Doors Open Toronto festivities. The green roof is a triumph. In reclaiming this space, Mr. Miller has, for $2.3-million, created a new public park in the city’s heart, environmentally sound and breathtakingly beautiful.

“It certainly was [City Hall architect Viljo] Revell’s vision to animate the space, for there to be cafes and people and for it to be a well-used space, but it was never realized,” said Sheila Glazer, manager of strategic policy in the city’s facilities office, standing on the green roof. “I think he would be excited by this.”

The vast space – almost equal to Nathan Phillips Square at ground level – provides a badly needed template of built credibility for the city’s recently introduced green roof by-law, which mandates green roofs on new and retrofit construction.

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 cost $2-million to landscape and is the first phase in the $42-million three-phase Nathan Phillips Square Revitalization at Toronto City Hall. The dramatic transformation was designed by competition-winning team of PLANT Architects in joint venture with Shore Tilbe Irwin & Partners with furniture designer Adrian Blackwell and Chicago-based landscape architect Peter Schaudt