Toronto's Mandatory Green Roof Bylaw--How effective are green building mandates?

On May 27, Toronto adopted a mandatory green roof bylaw, requiring green roofs on commercial, residential and industrial property. In summary, the bylaw requires

Up to 50 per cent green roof coverage on multi-unit residential dwellings over six storeys, schools, non-profit housing, commercial and industrial buildings. Larger residential projects require greater green roof coverage, ranging anywhere from 20 to 50 per cent of the roof area.

The mandatory nature of Toronto's green roof law kicked up a storm of controversy, with many developers objecting to the increased costs.

According to the Globe and Mail

Steve Daniels, a development planner with the Tridel Group, said a green roof can cost $18 to $28 a square foot on a typical tall condominium building, meaning an extra $200,000 to $400,000, plus maintenance costs.

The question remains: how effective are green building mandates in improving environmental outcomes like improving energy efficiency, water use, etc. ? Are they better than incentives? Less effective? To date, there is no study available on the regulatory effectiveness of green building mandates.  Such analysis needs to be undertaken soon before more requirements--which may or may not be the most effective means of acheiving environmental goals--are enacted.

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lloyd alter - June 2, 2009 4:28 PM

OK, I live in Toronto and know Tridel and used to work in the development industry. Let's take the average of the two costs per square foot, $23, and the average extra cost, $ 300,000. divide the two and you get an average floorplate of 13,000 sf. multiply that by the average tridel building height and you get a total area of 326,086 square feet. Divide the cost of the green roof by the square footage of the building and you get an additional cost of $1.08 per square foot of saleable area in the building.

Compare that to what they pay for newspaper advertising at 25K per weekend, or marketing, or commissions, or whatever, it amounts to absolute peanuts. They spend more throwing in the granite counters in the kitchens.

Governments do all kinds of things that add costs to buildings. They ask for insulation and other costly things that reduce energy consumption and push costs onto the developer who would be perfectly happy to let the purchaser pay for. That is why we have governments, to set standards. And green roofs are no different.

Hal Knowles - July 6, 2009 1:48 AM

Lloyd, I appreciate your perspective and share your philosophical belief that one role the government should play is to "set the rules to the game" to drive market innovation around issues of public health and safety and environmental protection and fair, sustainable, and equitable use of the commons (i.e. the Earth).

That said, and having been a LEED-AP since 2001, I am highly skeptical about the efficacy of some green building claims and am growing increasingly concerned about the lack of forethought being put into government incentives and mandates. Simply referencing certifications like the USGBC LEED Rating System only ensures achievement of outputs (i.e., one-time checklists and plaques) instead of outcomes (i.e., measurable and maintainable reductions in impacts). This is because LEED, like Energy Star and a myriad of other systems, are all rooted in models of performance and presumptions of compliance. Yes, these models may work on the engineered controlled environment of paper or digital design software, but they are only a part of the social-technological ecosystem that is an occupied building. And I would argue an unoccupied building is not a building, but merely a semi-organized lump of matter transformed from a previous state via a massive infusion of energy.

Here in Florida our stormwater regulations are the same way. Though I'm proud to say that Florida's water regulations are better than most states, the presumed compliance inherent in our stormwater permits have allowed the continued degradation of our state's water bodies and many are now entering TMDL status requiring hundreds of millions of dollars in mitigation to fix problems that have arisen from an engineered-only mindset that overly focused on designing for water quantity and not water quality and forgot about the human dimension of nutrient source control and system maintenance.

So circling back to the green roof debate as a microcosm of Shari's concerns, I leave you with a few questions.

1. What is the purpose of a green roof?
2. Is a green roof the most effective approach to achieving this purpose?
3. How do you measure compliance?
4. How do you learn from your failures and adjust regulations accordingly?
5. Does prescription trump prevention/performance?

I ask these questions because we've got scientists at the University of Florida who are currently researching green roofs. There are some suggestions that they don't really do much to improve water quality because the rainwater hitting these roofs hasn't been affected by the pollutants in the stormwater running along the impervious surfaces and manicured landscapes of the ground scale urban infrastructure. Additionally, in Florida green roofs actually require more water use to irrigate the plants because we have a climate of extremes defined by dry spells and seasons of short but intense bursts of rainfall.

On the other hand, if a green roof is used for the purpose of saving energy or reducing the urban heat island effect, then there are some suggestions that it may be a suitable strategy to meet these ends. However, is it the most cost effective strategy for all circumstances and should we be mandating prescriptive practices to try and achieve performance outcomes?...well that is a more difficult question...

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