OSPE Interviews P.Eng on Toronto's Green Roof By-Law
Q&A with Hitesh Doshi, P.Eng., Professor of Architectural Science at Ryerson University and Chair of the City of Toronto’s Technical Advisory Committee on Green Roof Construction Standards.

This is the first comprehensive Green Roof By-Law and green roof construction standard in North America. Did Toronto get it right?

The City of Toronto has been a global leader in terms of establishing meaningful practices related to urban green initiatives. The green roof by-law is one more example of a step in this direction. The benefits of green roofs in an urban environment are well documented. The City of Toronto worked with Ryerson University and was supported by the Ontario Centres of Excellence (OCE) and the Federation of Canadian Municipalities to determine the benefits of green roofs for the City of Toronto.

The by-law was implemented after careful research and examination of practices in the rest of the world. The City of Toronto staff has to be commended for the consultative approach taken to arrive at the by-law. They will certainly be open to suggestions for improvements as they learn from the implementation process.

The construction standard was based on a report by Halsall Associates, a Toronto engineering firm. It was developed through a consultative process by a technical advisory group consisting of various public stakeholders. The construction standard, along with the Ontario Building Code and other relevant standards, will ensure that green roofs are constructed using the best available knowledge.

What does the by-law mean for engineers in the GTA?

Engineers will need to familiarize themselves with the by-law and the construction standard. There are many types of new buildings which will require green roofs. Many of the performance aspects of green roofs will require engineering input. One obvious involvement relates to the design of the structure to accommodate the green roof design. Engineers will play an important role in terms of developing cost-effective structural designs. There are other areas where many engineers will find opportunities to participate. Some of these other areas relate to the performance of waterproofing green roof systems, drainage related to green roofs and its impact on stormwater considerations, and building code related issues such as fire and wind related design.

Who is qualified to design a green roof? Is a special permit/qualification necessary?

The process of designing a green roof will follow the same rules as the process of designing various aspects of a building as presently required in the Ontario Building Code. It is anticipated that architects and engineers will play the appropriate roles. It is also anticipated that architects and engineers will work in teams that will consist of landscape architects, and professionals who have acquired relevant educational qualifications by attending courses offered by industry organizations such as Green Roofs for Healthy Cities.

Why are there different requirements for residential and industrial buildings?

This particular issue was debated at various levels during the by-law development and formulation process. There does not appear to be a performance-related reason for such a decision. Partly the reason may be because of the wide variation in the types of uses that are captured in the industrial building category. It is also worth noting that the City wants to maintain and encourage industrial development to bolster employment. In the end, it is believed that this was the best choice to move the green roof by-law forward. It should not come as a surprise if this particular issue is revisited. It is hoped that design professionals involved with green roofs will be able to work with clients to develop solutions that are over and above the by-law.

Rooftops have become a hot commodity. With the passage of the Green Energy Act, developers will have incentives to install solar panels atop their buildings. Rooftop patios and recreational spaces are also becoming popular as a way to meet existing amenity space regulations. Is the green roof by-law competing for rooftop space?

This is a legitimate worry. There will be conflicts and there will be synergies. It will depend on the type of solutions that building owners are going to try to implement. One common situation would be the installation of solar panels along with a meadow type green roof. These two technologies are highly synergistic. The green roof reduces the surface temperature of the roof and studies have shown that this can be beneficial in improving efficiencies of rooftop equipment. There are installations where such technologies co-exist on the rooftop.

We are finally beginning to realize that there is some prime space on buildings in urban areas that has been under utilized. Rooftops can constitute almost 20-25% of the total urban surface area. The green roof by-law rightly takes into account available roof space minus the area for renewables, amenity space, and private terraces. We are moving in the right direction to make use of these spaces in some meaningful way. It is hoped that the implementation of the green roof by-law will take these types of competing uses into account.

With City Council having voted in favour of the by-law, what’s next?

The big challenge is to make sure that there will be a buy-in to this way of building roofs. For example, there are still rumblings that green roofs pose a considerable risk with respect to performance issues. Any new approach will require time to be successfully incorporated into status-quo. There are bound to be issues. However, nothing is insurmountable. We have been putting green roofs, patios and roads on top of our parking garages and underground spaces. We have learned to make them work. Engineers have played an important role in bringing innovative technologies into the mainstream. They will need to ensure that they play an important role in the design team to make sure that green roofs are designed to perform well.

In a few years, Toronto will look great from the ground and from the sky.