Water Balance, Quality & Efficiency for Low-Rise Residential Development

Construction Activity

Tier 1

WQ 1.1 Erosion and Sediment Control

Follow the Erosion and Sediment Control Guideline for Urban Construction during construction and demolition activities. (1)

Specifications and Resources

1. Refer to the Greater Golden Horseshoe Area Conservation Authorities Erosion and Sediment Control Guideline for Urban Construction.

Water Balance (Stormwater Retention)

Tier 1

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

Tier 2

WQ 2.2 Advanced 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

OR

Ensure that the total landscaped site area, located at and above grade, includes at least one of the following features:

1. A Green Roof covering at least 80% of Available Roof Space; ⁴
2. An Intensive Green Roof for 80% of the Green Roof Area provided; ^5,7
3. Biodiverse green roof to support pollinator species covering a minimum of 50% Green Roof Area; ^6,7
4. 25% of the Lot Area at or above-grade, planted with native flowering/pollinator species; ⁸
5. At-grade Bioretention facilities provided to capture and control 75% of runoff from on-site hardscape surfaces; or,⁹
6. Reforestation of a portion of the site, beyond the limit of a stewardship plan.¹⁰

Tier 3

WQ 2.3 Stormwater Retention and 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.^1,2,3,5

Specifications and Resources

1. Refer to the Wet Weather Flow Management Guidelines for additional detail.
2. 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.
   1. 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.
   2. 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.
3. Cash-in-lieu of Water Balance is not permitted.
4. 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.
5. 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:
   1. a deeper growing medium with a minimum depth of 150 mm; and
   2. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. Applications considering the At-grade Bioretention facilities or Reforestation options, email sustainablecity@toronto.ca to discuss your project.

Water Quality (Stormwater Run-Off)

Tier 1

WQ 3.1 Total Suspended Solids (TSS)

Remove 80 per cent of total suspended solids (TSS) on an annual loading basis from all runoff leaving the site based on the post-development level of imperviousness.¹

WQ 3.2 E.Coli Reduction

Control the amount of E. Coli directly entering Lake Ontario and waterfront areas as identified in the Wet Weather Flow Management Guidelines.²

Specifications and Resources

1. Refer to the Wet Weather Flow Management Guidelines for additional detail.
2. Refer to the Water Quality Targets for E.coli in the Wet Weather Flow Management Guidelines.

Water Efficiency

Tier 1

WQ 4.1 Drought-Tolerant Landscapes

Where potable water is used for irrigation, provide drought-tolerant plants for at least 50 per cent of the landscaped site area (including at-grade landscapes, vegetated roofs and walls).^1,2

Tier 2

WQ 4.2 Water Efficient Fixtures (Core)

Install water fixtures that achieve at least a 40 per cent reduction in potable water consumption for the building (not including irrigation) over the baseline water fixtures.^3,5

WQ 4.3 Efficient Irrigation (Core)

Where soft landscaping exists on the site, reduce potable water use for irrigation by 60 per cent. ^4,5

Tier 3

WQ 4.4 Water Efficient Fixtures (Core)

Install water fixtures or use non-potable water sources to achieve at least a 50 per cent reduction in potable water consumption for the building (not including irrigation) over the baseline water fixtures.^3,5

Specifications and Resources

1. Drought-tolerant landscapes and species are provided in accordance with the following City of Toronto guideline document, Drought Tolerant Landscaping: A Resource for Development. This requirement does not apply when non-potable water is used for irrigation.
2. In choosing tree species, preference should always be given to those native to the area. Where it can be clearly demonstrated that the planting of native tree species would not be appropriate due to site constraints often encountered in urban settings, Urban Forestry may accept non-native, non-invasive species better suited to the particular site.
3. Refer to LEED® V4 BD+C: WE Credit indoor water use reduction, for further details on how to achieve this requirement. Calculations will be based on estimated occupant usage and baseline fixtures including toilets, urinals, faucets, shower heads. Baseline fixtures include the following: toilets (6.0L), urinals (3.8L) residential faucets (8.3 LPM at 414 kPa), commercial lavatory (restroom) faucets (1.9 LPM at 414 kPa), shower heads (9.5LPM at 550 kPa).
4. Refer to LEED® V4 BD+C: WE Credit: Outdoor Water Use Reduction Option 2 for further details on how to achieve this requirement. Reductions in potable water must be calculated from a midsummer baseline case. Methods to reduce potable water use for irrigation include high-efficiency irrigation and use of captured rainwater and use of greywater.
5. Non-potable water sources include greywater or rainwater. Greywater may be used for subsurface irrigation if treated as per the requirements of the Ontario Building Code and CAN/CSA-B12.