Category: Articles

High Performance. Low Emissions. Future-Proofed

The Toronto Green Standard version 4 (TGS v4) raises the bar for all new development in the city. Green roofs play an important role especially on tight, urban sites. TGS v4 applies to all new planning applications in the City of Toronto received on or after May 1, 2022. Below is a review of the requirements and how green roofs help meet them.

Five performance categories:

Air Quality
Building Energy, Emissions & Resilience
Water Quality & Efficiency
Ecology & Biodiversity
Waste and the Circular Economy

Importance of Green Roofs

Green roofs, with their multiple benefits, play an important role in TGS v4 via 2 categories Water Quality & Efficiency (WQ) by Managing Stormwater and Ecology & Biodiversity (EC) through Landscape & Biodiversity.

WQ 1.1 Water Balance, Quality & Quantity Control

Tier 1 Water Balance requires the site to retain a minimum of 50% of the total average annual rainfall volume (or equivalent 5mm from each rainfall event) generated from all site surfaces through infiltration, evapotranspiration, water harvesting and/or reuse, in accordance with the Wet Weather Flow Management Guidelines (WWFMG).

Green roofs can retain rainfall through initial abstraction (IA). According to the WWFMG, the IA are 5mm and 7mm for extensive and intensive systems, respectively. Furthermore, stored water in the cistern can evapotranspirate on the green roof through irrigation water reuse. These mechanisms are key to achieve water balance on site. NLSM offers optional irrigation reports to support water balance calculations.

TGS v4 defines an Intensive green roof as having a minimum growing medium depth of 150 mm with a diverse mix of plants appropriate to the growing medium depth and roof height. On the other hand, extensive green roofs contain hardy, low-profile plants growing in less than 150 mm of growing medium.

WQ 1.3 On-site Green Infrastructure

Tier 1 requires the total landscaped site area, located at and above grade. It includes at least 1 of the following six green infrastructure features:

A Green Roof covering at least 80% of Available Roof Space
An Intensive Green Roof for 80% of the Green Roof Area provided
A Biodiverse green roof to support pollinator species covering a minimum of 50% Green Roof Area
25% of the Lot Area at or above-grade, planted with native flower/pollinator species
At-grade Bioretention facilities provided to capture and control 75% of runoff from on-site hardscape surfaces, or
Reforestation of a portion of the site (beyond the limit of a stewardship plan)

Note that three of the six options above involve green roofs. Putting green infrastructure on the roof is particularly attractive for development in tight urban sites with perhaps zero lot lines where there is little or no space to accommodate green infrastructures at grade.

The TGS v4 defines a Biodiverse green roof as an Intensive green roof that supports pollinator species. It is located at or below the 8^th storey of the building to maximize pollinator access and must 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 guide as listed below:

Increase depth of growing medium
Vary composition (structure) of growing media
Provide topographic variety
Provide microclimates
Diversity plant species
Provide perching habitat
Provide nesting opportunities
Provide water source (s)

A permanent irrigation system is required on both intensive and biodiverse green roofs to provide supplemental watering as necessary. Direct access to the roof should be provided for maintenance through a door or hatch located away from the edges to enable safe maintenance. A maintenance contract is recommended for at least the first 5 years of the green roof to ensure it receives a good start.

EC 2.3 Green and Cool Roofs

Landscape & Biodiversity Tier 1 requires buildings, where the Green Roof By-law is applied, to install a green roof to meet the minimum requirements as stated in the bylaw, or where the bylaw does not apply, provides 100% of the Available Roof Space with one of a combination of the following:

Green Roof
Solar PV, or
Cool roof

NSLM Green Roof Systems Comply with TGS v4

All NLSM green roof systems meet the TGS v4. NLSM offers optional professional engineer-stamped wind letter for submission to the City. This chart summarizes the compliance path and helps you select the system that best meets your project’s needs:

Categories^*	NLSM Systems	WQ 1.3 Compliance Options	WQ 1.1 Initial Abstraction^**
Extensive	LiteN’Less^TM II	80% of available roof space	5 mm
	LiteN’Less^TM III	80% of available roof space	5 mm
	StormCap^TM	80% of available roof space	5 mm
	StormCap^TM+Detention	80% of available roof space	5 mm
	TerraExt Sedum Standard	80% of available roof space	5 mm
	TerraExt with BioBerm	80% of available roof space	5 mm
Intensive	Flora Garden	80% of green roof area provided	7 mm
Biodiverse	Alpine Meadow	50% of green roof area provided	7 mm
	Alpine Meadow+	50% of green roof area provided	7 mm

* As defined by Toronto Green Standard version 4 (TGS v4)
** Based on Toronto Water’s Wet Weather Flow Management Guidelines (WWFMG)

Supplier of more than 2.5 M SQFT Coast-to-Coast

NLSM is Canada’s leading supplier of pre-vegetated roofs such as LiteN’Less™, Xeroflor® and StormCap™ systems. We customize to local requirements. Email or call (416) 637-5772 Ext 1.

Read Rooftop Stormwater Management Technologies for Climate Change Adaptation and Resilience by Dr. Karen Liu and Sasha Aguilera in Construction Canada January 2022 Vol. 64 No. 1.

The article looks at the increased intensity and frequency of recent extreme weather events such as heatwaves, rainstorms and hurricanes and how green infrastructure helps urban centres become more resilient. It includes info about new flood maps, efforts on climate action and how green infrastructure, including green roofs, blue roofs and blue-green roofs are being used to manage stormwater and mitigate flooding of urban centres.

Supplier of More Than 2.5 M SQFT Coast to Coast

NLSM is Canada’s leading supplier of pre-vegetated roofs such as LiteN’Less™, Xeroflor® and StormCap™ systems. We customize to local requirements. Email or call (416) 637-5772 Ext 1.

Read Wind Design Process for Modular Vegetated Roofing Systems by Dr. Karen Liu and Sasha Aguilera in Construction Canada January 2021 Vol. 63 No. 1.

This article was written by Next Level Stormwater Management’s Green Roof Specialist Dr. Karen Liu and Design Ambassador Sasha Aguilera – key participants in the research consortium that developed the first national wind testing standard for vegetated roofing. It explains the Canadian Standards Association (CSA) A123.24-15 Standard Test Method for Wind Resistance of Modular Vegetated Roof Assembly and explains the three simple steps that help determine a vegetated roof’s ability to withstand and protect against wind forces.

NLSM Provides P. Eng Stamped Wind Resistance Letters. Get Started! Contact us

Watch Video of NRC and UL Testing

More Than 2.5 Million Square Feet Coast-to-Coast

NLSM is Canada’s leading supplier of pre-vegetated roofs such as Xeroflor, LiteN’Less™ and StormCap™ systems. We are your one-stop-shop. We customize to local requirements, provide wind and stormwater calculations specific to location and building/roof type, P.Eng letters, and other documentation. We offer various products & services including warranty & maintenance support. Click here to start your design.

Reinventing the Traditional Green Roof for Detention by Sasha Aguilera and Brad Garner in Construction Canada January 2019 Vol. 61 No. 7.

Reinventing the Traditional Green Roof for Detention discusses how detention green roof systems are a reliable and quantifiable rooftop stormwater management tool. The article examines how to use detention technology in dense urban areas to help owners achieve ROI by saving valuable real estate while meeting municipal requirements.

Supplier of More Than 2.5 M SQFT Coast to Coast

Read Designing Vegetated Roofs to Survive Winter by Cristina Senjug in Construction Canada May 2018 Vol. 60 No. 3

The article discusses how in cold climates such as Canada, properly designed vegetated roofs, installed with hardy and mature plants that are well hydrated before winter, have a good probability of survival. If in the following spring, there is evidence of damage—caused by extreme temperature fluctuations, erosion due to high winds, or plant desiccation because of foot traffic—a basic repair is possible to help these sections quickly recover.

More Than 2.5 Million Square Feet Coast-to-Coast

Read Designing Extensive and Semi-Extensive Vegetated Roofs for Long-term Performance by Sasha Aguilera and Kees Govers in Construction Canada July 2016 Vol. 58 No. 5.

Awarded the 2017 F. Ross Browne Award for “Article of the Year”, this article co-authored by Sasha Aguilera and Kees Govers encourages consultants and contractors to think about their designs and implementations related to vegetated roofs in such a way that systems can perform as long as the building is in use. The article discusses everything from budgeting and design, to access, irrigation, wind uplift, designing for problem areas, care during construction, post-installation, maintenance, vegetation and overburden warranties. To ensure excellence in performance, it’s important the details in design and installation are considered as critically as the systems themselves.

More Than 2.5 Million Square Feet Coast-to-Coast

Read Waterproofing Considerations for Green Roofs by Dr. Karen Liu in Construction Canada March 2012 Vol. 54 No. 2

The article discusses the necessity of a robust and durable roofing system to provide a solid foundation for green roofs and tries to help answer, “What is the best roofing/waterproofing system for green roofs?