By Andrew Cole Yanders
Photo by Jorg Breuning
The focus of this academic exercise will identify a few of the leading psychological tendencies that drive up the costs of green roof installations. In a previous article we highlighted an impractical design that led to a “snowballing effect” of errors and costly mistakes. During the course of a green roof design and green roof specifications, decisions are constantly made that affect the final installation cost as well as future maintenance expenses. In any green roof design, it should be the goal to keep project costs for installation and green roof maintenance as low as possible without sacrificing the function. Experience, practical designing and resourceful engineering can make a dramatic impact on reducing the average market cost of installing a green roof.
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.
A fraction of the cost (approximately $1,000,000.00), more water retention and no irrigation needed an in-place system would be much more environmentally friendly. A monolithic or built-in-place system would be a highly efficient extensive, semi-intensive green roof according modern green roof technology.
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.
As soon as the Case Study is complete it will announced on our blog and available for download on our Resources page.
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