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Upcoming Case Study Announcement: The Podium Roof Garden at Toronto City Hall

Wednesday, December 14, 2011

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.

Click here for an emailed copy the case study upon it's release 

Kees Grovers commented on 03-Jan-2012 06:06 PM
I always love it when people talk about the successful green roofs that I have been involved with. It re-inforces that green roofs can be done successfully in North America by North Americans. And I encourage people to do case studies on successful green
roofs to see how and why they have succeeded and how their success can drive the rest of the industry forward. What bothers me about this blog posting is the fact that it is so devoid of facts and makes a number of assertions that have holes large enough to
drive a Mack truck through. Any case study should start with a check with the designer as to what the design intent was and whether that intent is being met. Considering that no-one bothered to contact the designers of this particular green roof before writing
the blog speaks volumes. The Design Competition that was staged for the revitalisation project at Nathan Phillips square was won by the design team in part on the basis of an instant green roof using pre-grown mature modules. The judges wanted to see a green
roof that looked like it had been there for years from day one for very good reasons. This green roof is in a very public location. It is overlooked by more than 100,000 people every day from City Hall and the surrounding office and hotel towers including
some of Canada’s most influential business leaders. It is accessed by several thousand people every day throughout the spring, summer and fall. To suggest that it could have been done as well and as quickly with a built in place system without irrigation is
totally disingenuous. The fact that the competition judges picked this design group over all the others was in good part due to the use of a finished green roof system. Is there a premium for instant? Of course there is. And as to ‘losing the originally designed
pattern of the tray system’. How do you know what the design intent was without talking to the designers. They certainly did not want it to look like the green roof was growing in trays. That is exactly the reason they chose the system they did. A hybrid modular
system that combines the best qualities of built in place, mats and modules all in one system. An instant monolithic green roof in modules. A built in place system with the same design would have taken 2-3 years to grow to the same stage that it was at on
the day it was installed. Time that wasn’t available in the construction and commissioning schedule. We accomplished the full establishment of the plants in the modules in the nursery in less than 3 months. A public green roof such as this needs to look good
from day one to get taxpayer buy in. Some money could have been saved (nowhere near the $1,000,000 claimed in the blog) by going the built in place route. However it would have resulted in howls of protest at the spending of taxpayers money on a ‘poor quality’
project. The general public, the media and politicians are very new to green roofs. They would not have appreciated a built in place system. As it was, when this project was officially opened on May 29, 2010, media outlets from the entire political spectrum
were universally praising the project. And they were lined up to do interviews with the designers and city officials for weeks prior to and after the opening. The green roof also became the most visited in Toronto during the next few days with over 20,000
visitors officially counted. And it is still in the media periodically in a positive light. That is and was a promotional coup for everyone in the green roof industry in Toronto, whether our system or anyone else’s. Of course it also has created a higher expectation
of what a green roof should look like. A number of other assertions made in the blog are also completely invalid. However for the sake of brevity, I will leave them alone for now.
Jörg Breuning commented on 04-Jan-2012 04:50 AM
Dear Kees Grovers, I appreciate your comments. The City Hall of Toronto project got my attention during a project presentation by the plant architect Vanessa Eickhoff at Ontario Green Roof and Wall Networking and Information Evening. During this extensive
presentation there was enough time to ask questions and getting the answers reflected in the upcoming case study. Before the presentation started I thought this project was still in the planning phase and I was carefully listening to the design intent what
made me already very upset. There are tons of projects in Northern America and in Europe that were trying to do the same but it never worked out. I couldn’t understand that there are multiple – so called- experts involved making decisions that are not based
on common knowledge only to polish their own ego and all generously paid by the tax payer while bringing the green roof industry in a bad light in the long run. Obviously it is all about quick attention and quick money. As the presenter started to show pictures
from the installation I understood that this project was already completed what led to many more questions and finally to my site visit. It didn’t take me long to discover lots of quality and performance issues already after the first year. As a green roof
advocate with the most experience in Northern America it is my responsibility to educate people – especially when tax payer money is involved or bylaws in place. This is very important to protect the industry and finally my job. We will inform when the case
study is available.

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