Toronto's Proposed Green Roof By-Law

There's no doubt that the blog has sucked for the past two weeks. My most sincere apologies. Let's just say that the combination of a family vacation and the responsibilities that occassionally arise from having what some might consider to be a "real job" don't exactly make for ideal blogging conditions.

How to get back on track? Why not combine the latter with this particular entry, and follow that up with the dysfunctional play-by-play of the former?

Consider this the first step in the triumphant return.






Go Green On Top, or Face $100,000 Fine, City Proposes
By Allison Hanes

Toronto is poised to become the first city in North America to make green roofs mandatory on most new buildings and set standards for their construction.

A city committee yesterday considered a proposed bylaw that would require roofs on new buildings with an area of 5,000 square metres or greater to be 30% to 60% covered by vegetation. The bigger the building, the more planted space it would have to have--otherwise fines of up to $100,000 could be levied.

As drafted, the bylaw would cover mid-to high-rise condos, retail space and office towers, but exempt low-rise, large-scale industrial, nonprofit housing and public buildings such as schools...

To read more, click HERE



Let me begin by saying that I've been actively involved in the drafting of this proposed by-law, sitting on various consultation committees and offering my opinions to both members of City Council and those involved with Green Roofs for Healthy Cities. And the fact that the City of Toronto is taking the required steps to move forward with this revolutionary by-law (the first such by-law in North America) just reaffirms my belief that I truly do live in the greatest city in the world. But by no means is this by-law the panacea for all of our city's various environmental ills. The fact is, this particular by-law has a loooooong way to go, and it leaves a great deal to be desired.

Is it a step in the right direction? Unquestionably. But it needs to have more than a few details ironed out, and it needs to have it's proverbial bar raised more than a few notches if it hopes to have any kind of appreciable impact.


You'll find below a copy of the letter I recently sent to Steven Peck, President of Green Roofs for Healthy Cities. It maps out the specific areas where I believe the by-law needs to be improved. Most of you probably won't care about the specifics, but for those looking to be able to speak intelligently about the by-law's shortcomings, here are your coles notes:

(To see the Draft By-Law, click HERE)


As a resident of Toronto and a firm believer in the benefits of vegetated roof assemblies, particularly in densely populated urban areas, I believe that it is of the utmost importance that, where green roofs are concerned, they need to be done right. That is to say, that they need to be specified with the aims of long-term sustainability and long-lasting durability in mind. Because in my opinion, the worst possible outcome for the green roof industry as a whole is to have institutions, businesses, and individuals sinking money into poorly designed and installed vegetated roof assemblies, resulting in inevitable failures that will invariably tarnish and damage what could otherwise be a magnificent step in the right direction for this city.

It is with this mindset that I have compiled the following thoughts for your consideration with regards to the City of Toronto's proposed Green Roof By-Law. I hope that you find these to be well informed, and of some use.


Important Considerations:


- Pertaining to Section 2 - Definitions

In Section 2, in defining the waterproofing membrane, the document stipulates that the membrane is the system “that resists hydrostatic pressure”.

I believe it is of the utmost importance that the waterproofing membrane in a vegetated configuration is one that is designed specifically to withstand hydrostatic pressure. In a vegetated configuration, the membrane should be a true waterproofing membrane, and not simply a water-shedding membrane. It is no secret that the membrane in a vegetated configuration will be under ponding water for much of its service life, and the membrane should be designed for these specific conditions (ie, if a membrane’s warranty is customarily voided when the membrane is under water for a period exceeding 48-hours, that particular membrane should not be considered to be in accordance with the Green Roof By-Law Standards for the City of Toronto).


- Pertaining to Section 5 – Waterproofing

When considering the type of membrane in a green roof system, I believe that the best possible system is a membrane in an inverted configuration, as conventional roofing membranes allow for water to saturate the insulation in the event of infiltration. Over a period of time, a minor breach in a conventional membrane will allow moisture to creep over a vast area of the insulation, thereby rendering that insulation ineffective and resulting in massive heating and cooling (energy) losses, eventually resulting in premature failure of the entire vegetated assembly.

I believe that the best possible membrane configuration for a vegetated roofing assembly is a fully adhered waterproofing membrane in an inverted configuration. A fully-adhered, inverted membrane will ensure that, should any water infiltrate the membrane, that water will have nowhere to run (provided that the membrane is fully adhered to a concrete deck). Furthermore, with a membrane in an inverted configuration, there will be no concerns regarding the saturation and subsequent ineffectualness of the poly-iso insulation in the event of a breach in the membrane.


- Pertaining to Section 5.3 – Water Retention

The benefits of stormwater retention in vegetated roof assemblies have been well documented, and I truly believe that there needs to be some kind of minimum standard for vegetated roof assemblies where water retention is concerned. There is little doubting the possible benefits of increased stormwater retention in densely populated, urban areas, and the proposed By-Law’s ignoring of these benefits, in my opinion, shows a true lack of priority and foresight.


- Pertaining to Section 6.1 – Growth Media

I am uncertain as to why the City of Toronto is choosing to follow the FLL Standard where growth media is concerned. By no means am I a Certified Professional Horticulturalist, but in my experiences, I have yet to come across many plant species that thrive more so in rocks and clay than in organic matter.

Furthermore, the FLL Standard growing mediums offer limited benefits with regards to stormwater retention, and in-turn oftentimes require irrigation for the survival of the vegetation over the course of the assembly’s life expectancy; a practice, it should be noted, which essentially goes against every plausible advantage a vegetated roof is supposed to impart.



It should be noted that I believe the City of Toronto’s attempt to implement minimum standards with regards to Vegetated Roof Assemblies is a noble one. I would just prefer that they raise the bar a little higher than they currently have it set, as doing so will benefit us all in the long run.


Sincerely Yours,

Sean McCallum