By Andrew Cole Yanders
Photo by Jorg Breuning
Instant green with pre-vegetated mats or tray systems are always much more expensive than built-in-place. Instant green requires much more maintenance to adapt the plants to the location or keep them in perfect conditions.
The City Hall in Toronto has already begun to loose the originally designed pattern of the tray system in the first year. The main cause for this is due of the lack of experience in maintaining this system. Judging by the transformation that has already taken place, the green roof will convert to a meadow style green roof in the next two years even when maintenance efforts are drastically increased.
A monolithic or built-in-place, seamless semi-intensive / extensive green roof on the City Hall of Toronto could have been installed for approximately half of the costs of the current modular system and would have had the same visual aspect today but with much less maintenance, no irrigation and less fertilizer.
Saving taxpayers money for the installation and the savings for required maintenance over the next decades should be the priority of responsible and experienced designers and planners. With the saved money – just from the installation - the city could have installed another 40,000 ft² green roof and which could have retained additional 614,295 gal of rain water per year that doesn’t need to be processed expensively in a treatment plant.