WQ 2.1 Stormwater Retention and Reuse
Retain runoff generated from a minimum of 5 mm depth of rainfall from all site surfaces through infiltration, evapotranspiration, water harvesting and reuse.1,2,3
WQ 2.2 Stormwater Retention and Reuse (Core)
Retain runoff generated from a minimum of 10 mm depth of rainfall from all site surfaces through infiltration, evapotranspiration, water harvesting and reuse.1,2,3
Ensure that the total landscaped site area, located at and above grade, includes at least one of the following features:
- A Green Roof covering at least 80% of Available Roof Space; 4
- An Intensive Green Roof for 80% of the Green Roof Area provided; 5,7
- Biodiverse green roof to support pollinator species covering a minimum of 50% Green Roof Area; 6,7
- 25% of the Lot Area at or above-grade, planted with native flowering/pollinator species; 8
- At-grade Bioretention facilities provided to capture and control 75% of runoff from on-site hardscape surfaces; or,9
- Reforestation of a portion of the site, beyond the limit of a stewardship plan.10
WQ 2.3 Stormwater Retention & Reuse (Core)
Retain runoff generated from a minimum of 25 mm depth of rainfall from all site surfaces through infiltration, evapotranspiration, water harvesting and reuse.1,2,3,
Specifications and Resources
- Refer to the Wet Weather Flow Management Guidelines for additional detail.
- Prioritize the use of green infrastructure and low-impact development practices including: tree and shrub plantings, green roofs and other landscaping to increase evapotranspiration from the site and to increase the amount of permeable surfacing on-site.
- Refer to the Green Streets Technical Guidelines for more details regarding at-grade green infrastructure design options and the City of Toronto Green Infrastructure Standards and Specifications for the Right-of-Way, for design and construction manuals.
- For water harvesting and reuse, applicants must demonstrate that the water demand would be equal or greater than the rainfall over the site; and ensure proper facilities to balance out any fluctuations in the rainfall and usage as much as possible. Allowable uses for harvested non-potable water include: flushing of water closets/urinals and sub surface irrigation. These uses are established under the Ontario Building Code.
- Cash-in-lieu of Water Balance will not be permitted.
- Refer to the Green Roof By-law for definitions of Green Roof and Available Roof Space, details on calculating the green roof area required and the Toronto Green Roof Construction Standard. Green Roof Area is the total roof area occupied by a Green Roof.
- Intensive Green Roofs have deeper substrates that can support a greater variety of plant species. They meet the definition of a Green Roof under the Green Roof By-law, and must include:
- a deeper growing medium with a minimum depth of 150 mm; and
- a diverse mix of plants appropriate to the growing media depth and roof height. Plants may include sedums, grasses, drought tolerant perennials, and larger plants and trees where appropriate.
- Biodiverse Green Roofs are designed to support pollinator species. They include an Intensive Green Roof that is located at or below the 8th storey of the building and follow the recommended plant species found in Appendix A of the Design Guidelines for Biodiverse Green Roofs, with at least two species in bloom at all periods over the growing season. The design must also address two or more applicable Design Strategies from section 4.2 of the Guideline.
- To support green roof performance, regular ongoing maintenance is requied for Intensive and Biodiverse Green Roofs. Install a permanent irrigation system to provide supplemental watering when necessary; provide direct access to the roof for maintenance through a door or hatch located away from the edge of the roof to enable safe maintenance and provide a Green Roof maintenance contract for at least the first 5 years of the green roof.
- Native plants provide pollen and nectar for food, as well as places to nest and overwinter for native pollinator species. At-grade planting areas must be deisgned to meet PollinateTO garden requirements. For suggestions on species selection, refer to the City of Toronto native wildflower, trees and shrubs lists. Above-grade planting areas must meet the requirements for a Biodiverse Green Roof to support pollinator species. Lot Area is the horizontal area within all the lot lines of a lot. Refer to City of Toronto Zoning By-law 569-2013.
- Bioretention facilities are structural stormwater controls effective at improving stormwater runoff quality and reducing total stormwater runoff using a combination of soil filter media and vegetation to filter, treat, temporarily retain, and infiltrate stormwater runoff. A bioretention facility typically consists of adequate pre-treatment, an inlet, a planting bed, a granular filter/storage reservoir, an underdrain, and appropriate outlet/overflow structures. Examples include: Bioretention Planters, Bioretention Curb Extensions/Bump-outs, Bioretention Cells and Rain Gardens.
- Applications considering the At-grade Bioretention facilities or Reforestation options, email email@example.com to discuss your project.