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Further Consultation on Toronto Green Roof By-Law

The City of Toronto is holding further consultations regarding the proposed Green Roof By-Law. These meetings are primarily dealing with the proposals about where the city should require green roofs on new construction (the current proposal is residential buildings with 20,000 m² GFA or more, and industrial/commercial/institutional buildings of 10,000 m² GFA or more).

The corollary document about how green roofs should be constructed — the proposed Toronto Green Roof Construction Guidelines — is still under development. From discussions I’ve had with the city, it seems that many of the points I raised in my last post are being considered. It sounds like some of the prescriptive requirements will be replaced with “best practice” guidelines and recommendations. There may also be some distinction made based on the overall size of the green roof being constructed … something I think is important for small-scale and residential green roofs.

I’m meeting with the city in the next few weeks to find out more about the construction standard and it’s development, so stay tuned.

In the meantime, if you are interested in attending one of the sessions dealing with the requirement for green roofs on new construction projects, you’ll need to RSVP. Here is the invite with the details, or visit the city’s website at for more and up-to-date information.

To whom it may concern:

Toronto’s City Planning Division is seeking your input on a proposed Green Roof By-law for the City of Toronto. This by-law, under the new authority of the City of Toronto Act, 2006, would require green roofs on certain types of new buildings and establish a standard for green roof design and construction in Toronto.

In December 2008, City Planning completed the first round of public consultations on where to require green roofs under the proposed Green Roof By-law. Staff considered the feedback received during the consultation period and recommended in a staff report to the January 8, 2009 Planning and Growth Management Committee that further consultation be undertaken and that staff report back to the Committee with a draft by-law in April 2009.

On February 16th and February 27th City Planning will be hosting consultation sessions to hear your comments on proposed options for requiring green roofs in the City of Toronto. You are invited to attend one of these meetings to provide your input on the proposed by-law. Toronto Building staff will also be on hand to provide an update on the Toronto Green Roof Construction Standard.

A third session is scheduled on February 18th to discuss revised proposals for industrial use buildings. This meeting is intended for owners of industrial buildings and industry representatives.

Information on the location of the meetings and a revised proposal to require green roofs will be circulated one week prior to the meeting date to participants who are registered for the session.

To register for the consultation please R.S.V.P. by Monday February 9th to Kerri Unger at and indicate which one of the following sessions you wish to attend:

Monday, February 16, 2009
Metro Hall, Room 308
55 John Street, Toronto
2:00 – 5:00 pm

Friday, February 27, 2009
Metro Hall, Room 309
55 John Street, Toronto
2:00 – 5:00 pm

Wednesday, February 18, 2009
(Industrial meeting)
2:00 – 5:00 pm

If you have any further questions please contact Shayna Stott at 416-392-0171.


My Comments on Draft Toronto Green Roof Construction Standard

TO: Dylan Aster,
Policy Advisor, Office of the Chief Building Official
c/o Green Roof Consultation
100 Queen Street West, 12th Floor, East Tower
Toronto, Ontario
M5H 2N2

RE: Green Roof Consultation Comments

My name is Colin Viebrock and I promote, advocate for, consult on, design and install small-scale green roofs.

If the proposed Toronto Green Roof By-law and draft Toronto Green Roof Construction Standard (TGRCS) are put into effect, I can guarantee that they will effectivly kill all small-scale green roofs in Toronto.


I started when, with the help of the City’s green roof subsidy pilot project, I installed a 40m² green roof on our garage. Throughout the learning and installation process, I “blogged” about our project at This led to inquiries from neighbours, several consultations, and eventually a handful of other green roof projects. Some have already been installed, some are in the design phase, and some are just waiting for the spring before being planted.

At the time of my garage project, there were no green roof installers in Toronto willing to take on a project of my size. Or, the estimates they gave me were considerably higher than I was looking to spend – in some cases, more than the entire cost of constructing the new garage!

I feel that the potential that green roofs offer for the city of Toronto lies not only in the large -scale industrial/commercial/institutional projects, but equally (if not more so) in the small-scale commercial and residential market. There are a large number of laneway garages that get rebuilt every year, each potentially contributing another 40m² of green roof. There are countless 2½-storey Victorian homes (with a partial flat roof at the back), low-rise apartment buildings, mixed commercial-residential buildings, and other residential structures … each a potential candidate for a green roof.

And, if the number of inquiries I receive is any indication, there is a strong desire on the part of the public for green roofs. Cost is always a factor, and my efforts have been to show the public that green roofs (with the proper guidance and design) can be inexpensive and/or do-it-yourself projects. No pun intended, but there is certainly a grass-roots movement in the city for small-scale green roofs. The By-law and draft TGRCS will kill this movement and eliminate all the potential environmental benefits that could be achieved.

Performance-Based, Not Prescriptive

The TGRCS must avoid prescriptive paths and instead define performance requirements. Prescriptive limits simply not work for small-scale green roofs.

The draft TGRCS (section 5.2) suggests a non-vegetated zone of 2m around the perimeter of non-occupied roofs, for safety reasons. It also suggest a non-vegetated zone with additional ballast for wind-uplift concerns (section 4.4) and possible fire protection (section 5.1).

I would point out that, if I had been required to provide a 2m non-vegetated zone around the perimeter of my garage, my green roof would be 90% smaller than it is now. I simply would not have built it.

Small-scale candidates for green roofs simply don’t have the overall width to support this size of non-vegetated perimeter. By my very informal estimation, a 6m wide lot would seem to be standard for the majority of houses in the downtown core. Requiring a 2m zone would automatically reduce the size for any potential green roof by a minimum of two-thirds.

This prescriptive requirement would kill the potential for green roofs on all but the largest of residential buildings … and again I offer that the greatest potential for widespread green roof adoption is on smaller structures.

Prescribing minimum depth requirements, too, could severely limit the construction of residential green roofs. Mandating a 15cm minimum depth (with a corresponding dead load of approximately 40 to 50 lbs/ft²) is unnecessarily onerous. Who decided on that depth? What about the dozens of vibrant, viable green roofs in Toronto – NOW Magazine, the Royal Ontario Museum, Hugh Garner Housing Cooperative, 401 Richmond and 215 Spadina – that survive on less than 15cm of growing media? What about all the residential applicants for the green roof subsidies in 2006-2007? Each one that is highlighted on the city’s website (save one) uses a system that is less than 15cm in depth.

If the goal of the TGRCS and the city’s green roof policies in general are to reduce urban heat island effects, reduce storm runoff, and save on building energy requirements, then the parameters of the TGRCS mirror those goals. Define a performance requirement for storm runoff, instead of a minimum depth.

I would also point out that several suppliers of green roof products make systems specifically designed to work within lower load constraints (i.e. thinner assemblies). Some of these companies are based in the GTA and southern Ontario. The draft TGRCS would mean that those products could no longer be used in Toronto. I hope this doesn’t open up the city to any kind of anti-competitive lawsuits. At the very least, it will drive all small-scale green roof industry – installations and employment – out of the city.

Finally, what is the benefit of defining a minimum depth at all for a green roof that doesn’t fall under the proposed By-law? I can see the logic in making parameters for those green roofs that are required (so the developers don’t “skimp” at put up a roof that will survive only as long as necessary). But why bother with people who are installing green roofs because they want to? Isn’t any type of green roof, no matter the size or depth, a benefit to the city and the environment? Again, the TGRCS will kill all construction of these smaller-scale projects.

Structural Design Requirements

I am always quick to point out to those who ask that not all buildings are viable green roof hosts, and that structural loading is the primary issue. I am then, of course, in full support of the provision in the draft TGRCS that requires the services of a Structural Engineer to account for the additional loads on required green roofs. However, I would strongly insist that the following section of the draft be maintained in the final standard:

4.1 Structural Loads and Procedures
If building structural members are to be sized based on tables within Part 9 of the OBC, care should be taken to ensure that the loads imposed by the green roof are within the limits required for use of the tables.

For smaller scale green roofs, especially on uninhabited structures like garages, sheds, and other outbuildings, if the structural members can be designed within the limits of the Part 9 tables, then I suggest that this be sufficient evidence of structural soundness. This will reduce one “barrier to entry” for anyone considering a smaller scale green roof.

Load Definition

The draft TGRCS suggests that green roof loads be calculated following the protocol provided by the ASTM standard: “ASTM E2397.05 – Standard Practice for Determination of Dead Loads and Live Loads Associated with Green Roof Systems” and “ASTM E2399.05 – Standard Test Method for Maximum Media Density for Dead Load Analysis of Green Roof Systems”.

Again, this is an unnecessary onus to put on a homeowner or designer of small-scale green roofs. If the construction details of the proposed green roof are outlined in the building permit application (i.e. various layers and component products used), and accompanying literature outlining the weights of each component (saturated and non-saturated), this would provide enough detail to determine the overall load imposed by the green roof.

As well, if a particular assembly has been used successfully on previous projects, than evidence of that assembly’s suitability should be sufficient.

Plant Selection

The draft TGRCS (section 7.2) suggests that:

The design of the green roof assembly shall be stamped by a Landscape Architect registered in the Province of Ontario.

Again, while this will prevent developers of green roofs required under the proposed By-law from doing the bare minimum, this is an undue requirement for small-scale green roofs and will kill the majority of these projects.

I agree that the components chosen for a green roof assembly, especially the vegetation layer, need to be compatible with the local climate and conditions. But, in my experience, this can be achieved through knowledgeable green roof consultants and installers, horticulturalists and gardeners (particularly those experienced with native, alpine, and/or drought-resistant species), and simply through trial-and-error.

A dedicated home-owner will want to maintain their green roof because of the energy savings and aesthetic qualities it brings when it is healthy and thriving. With no intended disrespect for their profession, requiring that homeowners enlist the services of a Landscape Architect (who, incidentally, may have no experience with green roofs), seems onerous.

By-Law Scope

The proposed By-law would require green roofs only on buildings greater than 10,000m² (20,000 for residential), yet the TGRCS would apply to all green roofs no matter the size. As I’ve discussed, this will actually be a hindrance to anyone who simply wants to install a green roof but doesn’t have to.

However, why were these numbers chosen? If the goal of the city’s green roof policies is widespread implementation of green roofs in Toronto, why not require green roofs on smaller buildings? Why is one 10,000m² green roof any more desirable than ten 1,000m² green roofs … or a thousand 10m² roofs for that matter?

The only reason I can imagine is that economies of scale make a larger green roof “more affordable” than many smaller ones. This is exactly the situation I ran into with my garage three years ago.

But the environmental benefit is no different. The only person who benefits from the economies of scale are the large-scale green roof suppliers who simply aren’t set up to deal with 100m² projects.

It seems counter-intuitive to require them on structures that are either not conducive to their longevity (think tall, thin condo towers) or where it is economically restrictive (industrial development, as discussed in Part A of Staff Report BLD2008PGM007), and to actively discourage, through overly restrictive, “one size fits all” requirements, building owners who want green roofs from installing them.

Plus, where are the incentives for green roofs? I’m not necessarily talking about monetary subsidies, although I strongly feel they should continue. What about relaxing the landscaping open space requirement for projects with a green roof, or at least considering the green roof area part of the open space? I would hazard to guess that that incentive alone would do more to encourage green roof adoption more than any other.


I am in full support of the city’s overall initiative to promote the adoption of green roofs. I am a happy recipient of two green roof subsidies, and have guided several other homeowners into the program as well.

While I applaud the efforts by the city to develop a standard by which permit applications for green roofs can be judged, I feel that the proposed Green Roof By-law and Toronto Green Roof Construction Standard will do nothing to promote the adoption of small- to medium-scale green roofs. They will, in fact, discourage people from installing them, drive business and development out of the city, and effectively kill the green roof movement in Toronto just as it is starting to take root.


Colin Viebrock
Green Garage
235 Rushton Road, Toronto, ON, M6G 3J4

Ann Borooah, Chief Building Official and Executive Director, Toronto Building
Gary Wright, Chief Planner and Executive Director, City Planning Division
Jane Welsh, Project Manager, Policy and Research, City Planning
Merle MacDonald, Planning and Growth Management Committee
Rose Bettencourt, Planning and Growth Management Committee
Councillor Norm Kelly, Chair, Planning and Growth Management Committee
Councillor Frank Di Giorgio, Planning and Growth Management Committee
Councillor John Filion, Planning and Growth Management Committee
Councillor Peter Milczyn, Planning and Growth Management Committee
Councillor Karen Stintz, Planning and Growth Management Committee
Councillor Adam Vaughan, Planning and Growth Management Committee
Mayor David Miller
Deputy Mayor and Councillor Joe Pantalone
Councillor Joe Mihevc

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Proposed Toronto By-Law Will Kill Small-Scale Green Roofs in City

The City of Toronto is considering a By-law that will require green roofs on certain types/sizes of new construction. As a part of this By-law, there will also be a Toronto Green Roof Construction Standard governing how a green roof should be designed/built.

The problem lies in that fact that this Standard will apply to all green roofs, required or not, regardless of their size. Some of the draft standards, however, are excessively onerous for small-scale projects. Some would outright make it impossible for small-scale green roofs to be built at all. If my garage had been subject to these standards, it would have only allowed to have been 10% the size, the structure would’ve needed to be beefed up considerably because I would’ve been mandated to use a deeper depth of growing media … and I probably wouldn’t have proceeded at all.

The documents outlining the By-law and construction standard are here and here, and my response letter to the city is available for your perusal here.

Please: if you are a strong advocate for green roofs and don’t want to see Toronto’s fledgling green roof movement die before it gets off the ground, send a letter to the city!

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