503B: Green Roof for Stormwater Management: When Form Meets Function

September 22, 2022

9:00 AM - 9:30 AM

The Toronto Green Standard requires a site to retain a minimum 50% of the total average annual rainfall volume generated from all site surfaces through infiltration, evapotranspiration, water harvesting and/or reuse. In many cases where there is zero lot line, the green roof becomes the only landscape that can retain/infiltrate rainfall on site. Any runoff is stored in a storage tank, to be pumped back later to irrigate the green roof and returned to the atmosphere through evapotranspiration. The green roof is often the key, if not the only stormwater management tool, to achieve the water balance target.

Despite of the important role that a green roof plays in meeting the site's water balance target, it often comes as an afterthought. The architect and civil engineer would bring in the landscape architect to put in a green roof after the building design is mostly completed, and the team would scramble inefficiently with the green roof size and design to meet the water balance target. A successful green roof requires collaboration of many disciplines.  Landscape architects are uniquely trained to lead the design team and collaborate with colleages in architecture, engineering, agronomy and horticulture. 

In the first part of this presentation, Karen Liu will explain how to design green roofs to manage stormwater and meet water balance target. Armed with this knowledge, a landscape architect can come to the table sooner rather than later, become a valued member of the design team, expand his/her scope of work and take on a leadership role in the integrated design process. In the second half of the presentation, landscape architect Patrick Li will focus on a case study that demonstrates how a landscape-architect-led design team created a beautiful green roof not only to meet water balance target on site, but also contributes to the users' enjoyment as functional and visual amenities.

Speakers