Difference between revisions of "Green roofs"

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[[File:GRmodules.png|thumb|500px|Example schematics of extensive green roofs. On the left, a 'built up' system comprising layers: roofing membrane, drainage board, geotextile, planting medium and sedum mat; and on the right a pre-planted plastic module or tray.]]
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===Overview===
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==Overview==
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Green roofs were traditionally employed for insulation and increased resiliency in cold climate regions of Europe. Modern green roofs are a rapidly developing  commercial market in Ontario. Their primary benefit is in maximizing evapotranspiration for water balance targets.
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Modern green roofs are a rapidly developing  commercial market in Ontario. Their primary benefit as a LID technology is in maximizing [[evapotranspiration]] for water balance targets.
  
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{{TextBox|1=Green roofs are ideal for:
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Take a look at the downloadable Green Roofs Planning and Design Factsheet below for an overview of this LID best management practice:
 +
 
 +
{{Clickable button|[[File:G.R.png|125 px|link=https://wiki.sustainabletechnologies.ca/images/b/be/LID_poster_-_Green_Roof_final.pdf]]}}
 +
 
 +
 
 +
Green roofs are sometimes referred to as 'eco-roofs', 'vegetated roofs', or 'living roofs'.
 +
{{textbox|Green roofs are ideal for:
 
*Sites without significant space at ground level for infiltration,
 
*Sites without significant space at ground level for infiltration,
 
*Zero-lot line projects with outdoor amenity requirements,
 
*Zero-lot line projects with outdoor amenity requirements,
 
*Projects looking for accreditation with LEED v.4}}
 
*Projects looking for accreditation with LEED v.4}}
  
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<p><strong><textprimary>The fundamental components of a green roof are:</textprimary></strong></p>
+
Extensive green roofs are the most common type being applied for stormwater management purposes in Ontario.
−
;-the roof area (being able to withstand the load)
+
Intensive green roofs are commonly used for amenity space on medium- and high-rise residential developments or sometimes as urban farms. They are sometimes referred to as roof gardens and encompass diverse uses, design priorities and technical specifications.  In the most extreme examples, many urban parkettes  including large shade trees may be included in this class, if they have parking garages beneath. As such the discussion on this page is limited to extensive green roofs.
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:-a drainage layer
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:-a filter layer
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{|class="wikitable"
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:-a layer of planting medium
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|+ Types of green roofs: defined by construction depth
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:-plants
+
|-
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<p><strong><textprimary>Additional components may include:</textprimary></strong></p>
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!Property
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:-an irrigation system
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!Extensive
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:-preformed tray modules
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!Intensive
 +
|-
 +
!Planting medium depth
 +
|10 - 15 cm||> 15 cm
 +
|-
 +
!Loading
 +
|up to ~250 kg/m<sup>2</sup>||Limitless where 'roof' is at ground level
 +
|-
 +
!Cost
 +
|Typically lower||Higher, including structural accommodations and plant selection
 +
|-
 +
!Maintenance
 +
|Depends highly on the aesthetic expectations of stakeholders||Will be comparable to other landscapes, depending on access requirements.
 +
|-
 +
!Stormwater benefit
 +
|Provides best cost-benefit balance||Varies highly
 +
|-
 +
!Biodiversity benefit
 +
|Lower, depends on planting||Greater potential, depends on planting
 +
|-
 +
!Amenity benefit
 +
|Usually visual only<br>i.e. inaccessible||Often accessible
 +
|}
 +
 
 +
'''The fundamental components of an extensive green roof are:'''
 +
*a roof structure able to support the design load
 +
*a waterproof membrane resistant to root penetration
 +
*a drainage layer
 +
*a filter layer
 +
*a layer of planting medium
 +
*plants
 +
 
 +
'''Additional components may include:'''
 +
*an irrigation system
 +
*pre-formed tray modules
 +
 
 +
==Planning considerations==
 +
[[File:TBG2005.jpg|thumb|Sloped extensive green roof at Toronto Botanical Gardens, designed with four species of Sedum (Image: Terry McGlade)]]
 +
[[File:TBG2014.jpg|thumb|Same extensive green roof illustrating the increased biodiversity resulting from very light maintenance over 10 years]]
 +
 
 +
Green roofs offer a variety of co-benefits beyond stormwater management. In urban centers they are often constructed to accommodate a roof terrace or amenity space. In this scenario, the direct stormwater capture benefit is restricted to the areas with vegetation planted.  Another increasingly popular use for rooftop space is for urban farming. Again, the direct stormwater capture benefit is restricted to the areas with planters.
 +
To maximize the utility of a green roof as a low impact development tool, coverage with planting should be maximized. In many cases this means only inaccessible spaces are used.
 +
 
 +
===Amenity===
 +
Roof gardens with a high proportion of impermeable surface are popular in high rise developments. These amenity terraces are often described as green roofs, but the LID benefit applies only to the vegetated areas. The stormwater benefit of all kinds of green roofs is maximized by combined with [[rainwater harvesting]] for subsequent irrigation. Sedum and native species have all been shown to thrive with daily irrigation to saturation<ref>University of Toronto. 2017. gritlab. https://grit.daniels.utoronto.ca/</ref>.
 +
 
 +
Rooftop farming is also becoming common in some Ontario cities. Again consideration should be given to the proportion of the roof actually planted. Where large open expanses of roof are being cropped, measures may be required to reduce erosion of exposed planting medium. Any digging or furrows will reduce the stormwater benefit.
 +
 
 +
===Biodiversity===
 +
Biodiversity opportunities are optimized by planting a variety of species. General advice on this has been prepared by the City of Toronto<ref>City of Toronto. 2017. Biodiverse Green Roofs. https://www.toronto.ca/city-government/planning-development/official-plan-guidelines/green-roofs/biodiverse-green-roofs/</ref>. In the long term, the richness of species increases owing to 'volunteer species'. The desirability of this diversity varies with the aesthetic concerns of the green roof owner.
 +
 
 +
==Design==
 +
[[File:TD Bank.jpg|thumb|The vegetation on this extensive green roof is designed to withstand the deep shade of being in downtown Toronto.]]
 +
 
 +
===Roof===
 +
Flat roofs should be graded without depressions, with positive drainage ≥ 2% (1:50) towards roof drains.  For roofs with pitch greater than 10 % (1:10) additional geo grid or cellular components should be included in the design. These structures reduce the flow rate of the draining water, and help to stabilize green roof components. Green roofs can be installed on slopes greater than 20 % (1:5), but specialized design advice should be sought for the addition of components required to secure the green roof in place.
 +
Extensive green roofs do not require additional insulation layers. The underlying roof may be of  warm, cold or inverted design.
 +
Extensive green roofs add load of around 70 - 300 kg/m<sup>2</sup>. A structural engineer should be consulted during design to account for the distributed loads including [[Winter|snow]] accumulation and live loads including maintenance staff.
 +
Roof membranes should be waterproof, root resistant, resilient to temperature change, and comply with appropriate CGSB standards as specified in the Ontario Building Code. In most cases a new roof with a modern membrane will not require a separate root penetration barrier.  In retrofit scenarios an additional root barrier may be recommended to protect an older roof membrane.
 +
 
 +
===Drainage Layer===
 +
The underlying drainage layer is most often a preformed plastic sheet, formed to include depressions for water storage and perforations to drain excess water. This design has the advantage of being most lightweight, but has minimal impact on flow rates once the water has percolated onto the roof membrane below.
 +
An alternative drainage layer solution is to use a granular medium to increase the tortuosity of the flow path and slow peak flow rates.
 +
 
 +
===Filter Layer===
 +
The [[Geotextiles| geotextile]] layer is included to prevent migration of the planting medium into the drainage layer.  Current advice is to specify a free draining textile to prevent potential water-logging of the planting medium. Observations green roof assemblies have shown a reduction of flow from specifications owing to interactions of medium particles with the textile.
 +
 
 +
===Growing Medium===
 +
{{:Green_roof_media}}
 +
 
 +
===Irrigation===
 +
Regular irrigation has been shown to substantially reduce the stormwater capture benefit of an extensive green roof<ref name=Hill/>. 
 +
One way to reduce the irrigation used on green roofs is through the use of smart technologies. Responsive sensors that suppress irrigation after a rainstorm are routinely attached to green roofs to conserve water. Improvements can be made by instead using a 'soil' moisture sensor to trigger irrigation. State-of-the-art management systems now use predicted weather data to suppress irrigation ahead of storm events, see [[digital technologies]]. 
 +
Due to their limited water retention capacity, many green roofs are coupled with a rainwater harvesting cistern, to capture the excess water. It then becomes desirable to use as much harvested water to regain the cistern capacity,  Green roofs can be irrigated to saturation daily throughout the growing season without damaging the vegetation.
 +
 
 +
{|class="wikitable"
 +
|-
 +
!Irrigation technology
 +
!Benefits
 +
!Disadvantages
 +
|-
 +
!Spray
 +
|Maximizes evaporation||Requires higher water quality
 +
|-
 +
!Drip or capillary
 +
|Harvested rainwater is readily used without further treatment<br>Uses less water||Planting medium does not 'wick' water sideways readily, so can lead to localized dry areas
 +
|}
 +
 
 +
Maximizing evaporation with spray irrigation is the faster way to empty a stormwater cistern, and provides some cooling benefit for the building and it's surroundings.
 +
 
 +
===Planting===
 +
The choice of vegetation on an extensive green roof is insignificant in stormwater management compared to the choice of planting medium or the provision of irrigation. The vegetation should be selected to be resilient to both very wet and very dry periods.''Sedum'' species are the most common choice, demonstrating excellent longevity in systems with or without irrigation.
 +
Some projects expect the low growing ''Sedum'' to  remain in graphic designs according to species and flower color. This is not a realistic expectation without significant maintenance costs. Instead project stakeholders should be prepared early in the design process to embrace the green roof as a living and evolving ecosystem. Designs which incorporate both ''Sedum'' and native species can help with this.
 +
 
 +
===Drains and vegetation free zones===
 +
Vegetation free areas are often required around the perimeter of the roof to reduce wind uplift, on larger areas requiring firebreaks, for access paths and around drains.  To prevent accumulation of sediment and migration of the vegetation, the vegetation free areas should not be filled with decorative aggregate or river rock.  Instead concrete pavers or other surfaces that do not actively trap particles will reduce weeding maintenance.
 +
 
 +
===Design for ease of maintenance===
 +
The primary operational concern for operating a green roof is the development of a leak. Green roofs protect the roof membrane from UV damage and should increase the lifespan of the roof. However, in the event that a leak is discovered a section of green roof would have to be removed for access. Some proprietary systems appear to be easier to remove and replace. This may come at a cost, as the rainwater retention of the system is somewhat reliant on continuous coverage of the green roof surface.
 +
 
 +
Green roofs should receive as little maintenance as possible. Regular inspection is only required to see that the drains are free from obstruction and that the vegetation coverage is adequate to prevent wind erosion. During detailed design, all areas adjacent to the green roof itself should be kept free from granular material. Sediment accumulates in  gravel edging, which then permits the vegetation to take root and spread.
 +
 
 +
<gallery mode="packed">
 +
Roof Drain.jpg | Example of gravel edging around a roof, which needs weeding.
 +
Red Drain.jpg| Example of gravel edging around a roof drain, which needs weeding.
 +
Native Child.jpg| The amenity value of this roof is enhanced by the tall and climbing plants screening the high safety fences.
 +
PondRd2.jpg| Very light maintenance has permitted a stand of Mullein to develop on this prairie style green roof, increasing the biodiversity value.
 +
</gallery>
 +
 
 +
==Green roof plants==
 +
<div class="mw-collapsible-content">
 +
{{:Green roofs: Planting}}
 +
</div></div>
 +
 
 +
Aesthetics of the planting should consider that the practice may be viewed from above.
 +
 
 +
==Construction==
 +
Refer to the [[Green roof construction]] page for detailed guidance on construction best practices.
 +
 
 +
==Inspection and maintenance==
 +
Green roof maintenance is typically greatest in the first two years as plants are becoming established. Vegetation should be monitored to ensure dense coverage becomes established. A warranty on the vegetation should be included in the
 +
construction contract.
 +
Regular operation of a green roof includes:
 +
* [[Green roofs#Irrigation|Irrigation System]]: Watering should be based on actual soil moisture conditions as plants are designed to be drought tolerant. High soil moisture from unnecessary watering will reduce the runoff reduction benefits of the green roof.
 +
* [[Green roofs#Design|Leak Detection]]: Electronic leak detection is recommended. This system, also used with traditional roofs, must be installed prior to the green roof. Particular attention to leak detection should be paid in the first few months following installation (The Folsom Group, 2004).
 +
Ongoing maintenance should occur at least twice per year (Magco, 2003) and should
 +
include:
 +
* [[Green roofs#Design for Maintenance|Weeding]]: Remove volunteer seedlings of trees and shrubs. Extensive green roofs are not designed for the weight of these plants, and the woody roots can damage the waterproofing.
 +
* [[Green roofs: Planting|Debris and Dead Vegetation Removal]]: Debris and bird feces should be removed periodically. In particular, the overflow conveyance system should be kept clear.
 +
 
 +
<br>
 +
Take a look at the [[Inspection and Maintenance: Green Roofs]] page by clicking below for further details about proper inspection and maintenance practices:
  
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----
+
{{Clickable button|[[File:Green roofs cover page.PNG|150 px|link=https://wiki.sustainabletechnologies.ca/wiki/Inspection_and_Maintenance:_Green_Roofs]]}}
  
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===Planning Considerations===
+
==Life cycle costs==
−
<p>Green roofs offer a variety of co-benefits beyond stormwater management. In urban centres they are often constructed to accommodate a roof terrace or amenity space. In this scenario the stormwater capture benefit is restricted to the areas with vegetation planted. Another increasingly popular use for rooftop space is in urban farming. Again the stormwater capture benefit is restricted to the areas with planters.</p>
+
To learn about Life Cycle Costs associated with this practice (i.e. Pre-construction, Excavation, Materials & Installation, Project Management, Overhead, Inspection and Maintenance, Rehabilitation and other associated costs), visit the [[Green Roof: Life Cycle Costs]] page to view a cost estimate for an extensive pre-grown mat green roof. Alternatively you can use the [https://sustainabletechnologies.ca/lid-lcct/ STEP's Low Impact Development Life Cycle Costing Tool (LID LCCT)] to generate cost estimates customized to your own LID stormwater design project specifications.
−
<p> To maximize the utility of a green roof as a low impact development tool, coverage with planting should be maximized. In many cases this means only inaccessible spaces are used. </p>
 
−
<p> Within the scope of green roof coverage, there is a further distinction made between 'intensive' systems over 15 cm deep, and the more commonly employed 'extensive' systems, which are 10-15 cm deep. Specialized, shallow systems exist but their application is limited. </p>
 
  
−
<h4>Loading</h4>
+
Take a look at the [[Green Roof: Life Cycle Costs]] page by clicking below for further details:
  
 +
{{Clickable button|[[File:Construction Breakdown GreenRoof No Infil.PNG|150 px|link=https://wiki.sustainabletechnologies.ca/wiki/Green_Roof:_Life_Cycle_Costs]]}}
  
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<h4>Amenity</h4>
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==Performance==
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<h4>Biodiversity</h4>
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[[File:YorkU1.jpg|thumb|Recently laid ''Sedum'' mats on a ground level podium roof.]]
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----
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[[File:YorkU2.jpg|thumb|Detail showing the early root development through the mat to the granular planting medium.]]
  
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===Design===
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{| class="wikitable"
−
<h4>Planting Medium</h4>
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|+ Ability of green roofs to meet SWM objectives
−
<p>In many proprietary systems the default option for planting medium will be a granular material with very low organic matter content. However, many companies can arrange for a high organic content alternative to be substituted if requested. </p> 
+
|-
−
The benefits of 'high organic' media are:
+
!Water balance benefit
−
<ol>
+
!Water quality improvement
−
<li>Increased water holding capacity, which benefits both vegetation health and stormwater retention, </li>
+
!Erosion control benefit
−
<li>Often lighter weight, even when saturated, </li>
+
|-
−
</ol>
+
|Partial: Through interception and evapotranspiration
−
The disadvantages of a 'high organic' planting medium are:
+
|No: Green roof runoff may contain elevated concentrations of some contaminants, particularly dissolved [[Phosphorus]], Nitrogen and [[Heavy metals]].
−
<ol>
+
|Partial: Through interception and evapotranspiration
−
<li> Increased phosphorous concentration in runoff water, however this may be mitigated by the reduced runoff volume resulting in a lower loading overall,</li>
+
|}
−
<li>The lightweight material is more prone to wind erosion, and this should be accounted for in the initial design, alternatives include erosion control blankets, soil tackifiers, or Sedum mats. </li>
+
===Water Balance===
−
</ol>
+
Green roofs are primarily a practice used to partially achieve water balance and erosion control objectives through interception and [[Evapotranspiration| evapotranspiration]] of precipitation that falls on the roof.  The key hydrologic benefit which green roofs have over other forms of LID is the proportion of the water returned to the atmosphere through [[Evapotranspiration| evapotranspiration]]. Considerable research has been conducted in recent years to define the runoff reduction or water retention capacity of extensive green roofs in climates similar to those that occur in Ontario and Canada.
  
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<h4>Planting</h4>
+
* Controlled studies have indicated that maturing green roofs may have improved water retention properties <ref>De-Ville, S., Menon, M., Jia, X., Reed, G., Stovin, V. 2017. The impact of green roof ageing on substrate characteristics and hydrological performance. Journal of Hydrology. Volume 547. pp 332-344. https://doi.org/10.1016/j.jhydrol.2017.02.006.</ref>.
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<p>The choice of vegetation on an extensive green roof is insigificant in stormwater management compared to the choice of planting medium or the provision of irrigation. The vegetation should be selected to be resilient to both very wet and very dry periods. <em>Sedum</em> species are the most common choice, demonstrating excellent longevity in systems without irrigation. </p>
+
* In Southern Ontario rainwater retention of extensive green roofs without irrigation is between 57% and 70%<ref>Liu, M. Minor, J. 2005. Performance evaluation of an extensive green roof. National Research Council of Canada. NRCC-48204 https://sustainabletechnologies.ca/app/uploads/2013/03/NRC_EastviewGRrept.pdf</ref> <ref name=VS>Van Seters, T., Rocha, L., Smith, D., MacMillan, G. 2009. Evaluation of Green Roofs for Runoff Retention, Runoff Quality, and Leachability, Vol. 44 (1): 33 - 47 (2009). Innovative Approaches to Stormwater Management in Canada https://sustainabletechnologies.ca/app/uploads/2013/03/WaterQualResearchJournalCanada_YorkU-Greenroof.pdf</ref> <ref name=Hill>Hill J, Drake J, Sleep B, Margolis L. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. doi:10.1061/(ASCE)HE.1943-5584.0001534</ref>.
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<p> However, some projects expect the low growing <em>Sedum</em> to remain in graphic designs according to species and flower color. This is not a realistic expectation without huge maintenance costs. Instead project stakeholders should be prepared early in the design process to embrace the green roof as a living and evolving ecosystem. </p>  
+
* Including winter periods with snow accumulation and thaw, the annual retention of extensive green roofs is around  50% <ref name=VS/><ref name=Hill/>.
 +
* Using a compost based planting medium improves retention by around 10% (i.e., 60% for compost compared to 50% for granular).
 +
* Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modelled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.
  
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----
+
An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>
 +
Fassman-Beck, E., Hunt, W., P.E. Robert Berghage, R., Donald Carpenter, D., Kurtz, T., Stovin, V., Wadzuk, B. 2016. Curve Number and Runoff Coefficients for Extensive Living Roofs. Journal of Hydrologic Engineering. Vol.21. Issue 3. ASCE. https://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001318</ref> <ref name=Hill/>.
  
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===Performance===
+
In a study to investigate how green roof runoff reduction performance is affected by climate, Talebi et al. (2019) used water balance and evapotranspiration models to simulate runoff produced by green roofs in six Canadian cities (Vancouver, Calgary, Regina, Toronto, London and Halifax).  Results showed that predicted runoff reduction performance varied from 17% to 50% for low water use plants.  The best performance was predicted to occur in Regina and Calgary (drier climates), while the poorest performance was predicted for Halifax and Vancouver (wetter climates).  Average annual runoff reduction was highest in Toronto and London and lowest in Vancouver.<ref>Talebi, A., Bagg, S., Sleep, B.S., O'Carroll, D.M. 2019. Water retention performance of green roof technology: A comparison of Canadian climates. Ecological Engineering, 126, (2019), 1-15. https://www.sciencedirect.com/science/article/abs/pii/S0925857418303835?via%3Dihub</ref>
  
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<h4>Water Quantity</h4>
+
===Water Quality===
 +
Many green roofs receive only rainwater, which is relatively free of contaminants like nutrients and heavy metals, but can contribute contaminants to roof runoff, most notably through leaching of dissolved [[Nutrients]] and [[Heavy metals]] from the growing medium substrate during early establishment.<ref>Hathaway, A.M., Hunt, W.F., Jennings, G.D. 2008. A field study of green roof hydrologic and water quality performance. Transactions of the ASABE. Vol. 51 (1) pp. 1-8. https://elibrary.asabe.org/abstract.asp?aid=24225</ref> <ref>Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub</ref>  Concentrations of Total [[Phosphorus]] in green roof runoff have been observed to vary from 0.4 mg/L to over 10 mg/L.<ref>Hill J., Drake J., Sleep B., Margolis L. 2017. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29HE.1943-5584.0001534</ref>. Such concentrations are well above the Ontario Provincial Water Quality Objective of 0.03 mg/L for Total Phosphorus (OMOEE, 1994<ref>Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.</ref>) to control excessive plant growth in rivers and streams. To improve the quality of runoff from green roofs, Vijayaraghavan et al. (2018) recommend considering the sorption capacity of the growing medium substrate, the phytoremediation potential of plants, and incorporation of sorbent [[Additives]] to growing medium substrates.<ref>Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub</ref>
  
 +
In dense urban centres, green roofs are increasingly being used to receive irrigation from harvested rainwater. Current Ontario Building Code permits the use of rooftop runoff for landscape irrigation purposes, so long as it is 'free of solids'.
 +
A 'closed loop' system can be created by coupling a rainwater harvesting system with a green roof and harvesting and reusing roof runoff as a source of water for irrigation during dry periods, so the only water leaving the system is through evapotranspiration. This can prevent runoff from leaving the site and thereby prevent contaminant loading to the environment.
  
−
<h4>Water Quality</h4>
+
[[File:TP.PNG|thumb|Total phosphorous concentrations reported in green roof runoff(abstracted from Hill 2017)]]
−
<p>Many green roofs receive only rainwater, which is relatively clean when it lands. As such green roofs can contribute contamination, most notably in nutrient leaching during early establishment. But, in dense urban centres, green roofs are increasingly being used to receive irrigation from harvested rainwater. Current Ontario Building Code permits the use of rooftop runoff to be reused in this manner, so long as it is 'free of solids'.</p>
 
−
<p> Where rainwater is harvested and reused to irrigate a green roof, there is no significant discharge of stormwater from the system, and no loading of contaminants downstream.</p>
 
  
 +
==Incentives and credits==
 +
===In Ontario===
 +
City of Toronto updated their [https://www.toronto.ca/services-payments/water-environment/environmental-grants-incentives/green-your-roof/ Eco-roof incentive program] in 2017. It now includes grants for green roof and cool roof structural assessments and is available to non-profit organizations.<ref>City of Toronto. 2017. Eco-roof Incentive Program. https://www.toronto.ca/services-payments/water-environment/environmental-grants-incentives/green-your-roof/</ref>
  
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----
+
===LEED BD + C v.4===
 +
<poem>
 +
LEED offer a relatively large number of points for green roofs compared to other LID technologies.
 +
[http://www.usgbc.org/node/2613129?return=/credits '''Sustainable Sites: Open space (1 point)''']
 +
This credit applies to accessible green roofs on tall buildings with little other outdoor space.
 +
[http://www.usgbc.org/node/2758192?return=/credits '''Sustainable Sites: site development - protect or restore habitat (up to 2 points)''']
 +
This credit applies to green roofs planted with 'native and adapted vegetation' on tall buildings with little other outdoor space
 +
[http://www.usgbc.org/node/2613950?return=/credits '''Sustainable Sites: Heat island reduction (up to 2 points)''']
 +
Green roofs are weighted as effectively as 'High-Reflectance' roofs in a simple calculation to determine the credit.
 +
</poem>
 +
{{:LEED: Rainwater management}}
  
−
===Incentives and Credits===
+
==External links==
−
<h4>In Ontario</h4>
+
*[https://www.greenroofs.org/ Green Roofs for Healthy Cities]
−
<strong>City of Toronto</strong> updated their 'Eco roof' incentive program in 2017 . It now includes grants for structural assessment and is available to non-profit organisations [http://www1.toronto.ca/wps/portal/contentonly?vgnextoid=e08354ae91cda510VgnVCM10000071d60f89RCRD].
 
−
<h4>LEED BD + C v.4</h4>
 
  
−
<h4>SITES v.2</h4>
+
===Proprietary systems===
−
----
+
{{:disclaimer}}
 +
*[http://www.ginkgosustainability.com/ Ginkgo Sustainability]
 +
*[http://www.liveroof.com/ LiveRoof]
 +
*[http://www.nlsm.ca/ Next Level Stormwater Management]
 +
*[http://www.vitaroofs.com/ VitaRoofs]
 +
*[https://www.zinco.ca/ Zinco]
 +
*[https://www.soprema.ca/en/sopranature-vegetated-systems/ Soprema]
  
−
===See Also===
+
==Green roofs gallery==
−
<ul>
+
{{:Green roofs: Gallery}}
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<li>[[Rainwater Harvesting]]</li>
 
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===External Links===
 
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<ul>
 
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<li>[https://www.greenroofs.org/ Green Roofs for Healthy Cities]</li>
 
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<h4>Proprietary Systems</h4>
 
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Links are provided for information only. Inclusion of a company or product does not constitute endorsement. <br>
 
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You may inform us of any omissions using the link below:
 
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<li>[http://www.nlsm.ca/ Next Level Stormwater Management]</li>
 
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<li>[http://www.liveroof.com/ LiveRoof]</li>
 
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<li>[http://www.ginkgosustainability.com/ Ginkgo Sustainability] </li>
 
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<li>[https://www.zinco.ca/ Zinco]</li>
 
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<li>[http://www.vitaroofs.com/ VitaRoofs]</li>
 
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</ul>
 
  
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==References==
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[[Category:Green infrastructure]]
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Latest revision as of 20:27, 2 August 2023

Example schematics of extensive green roofs. On the left, a 'built up' system comprising layers: roofing membrane, drainage board, geotextile, planting medium and sedum mat; and on the right a pre-planted plastic module or tray.

Overview[edit]

Modern green roofs are a rapidly developing commercial market in Ontario. Their primary benefit as a LID technology is in maximizing evapotranspiration for water balance targets.

Take a look at the downloadable Green Roofs Planning and Design Factsheet below for an overview of this LID best management practice:

G.R.png


Green roofs are sometimes referred to as 'eco-roofs', 'vegetated roofs', or 'living roofs'.

Green roofs are ideal for:

  • Sites without significant space at ground level for infiltration,
  • Zero-lot line projects with outdoor amenity requirements,
  • Projects looking for accreditation with LEED v.4

Extensive green roofs are the most common type being applied for stormwater management purposes in Ontario. Intensive green roofs are commonly used for amenity space on medium- and high-rise residential developments or sometimes as urban farms. They are sometimes referred to as roof gardens and encompass diverse uses, design priorities and technical specifications. In the most extreme examples, many urban parkettes including large shade trees may be included in this class, if they have parking garages beneath. As such the discussion on this page is limited to extensive green roofs.

Types of green roofs: defined by construction depth
Property Extensive Intensive
Planting medium depth 10 - 15 cm > 15 cm
Loading up to ~250 kg/m2 Limitless where 'roof' is at ground level
Cost Typically lower Higher, including structural accommodations and plant selection
Maintenance Depends highly on the aesthetic expectations of stakeholders Will be comparable to other landscapes, depending on access requirements.
Stormwater benefit Provides best cost-benefit balance Varies highly
Biodiversity benefit Lower, depends on planting Greater potential, depends on planting
Amenity benefit Usually visual only
i.e. inaccessible		 Often accessible

The fundamental components of an extensive green roof are:

  • a roof structure able to support the design load
  • a waterproof membrane resistant to root penetration
  • a drainage layer
  • a filter layer
  • a layer of planting medium
  • plants

Additional components may include:

  • an irrigation system
  • pre-formed tray modules

Planning considerations[edit]

Sloped extensive green roof at Toronto Botanical Gardens, designed with four species of Sedum (Image: Terry McGlade)
Same extensive green roof illustrating the increased biodiversity resulting from very light maintenance over 10 years

Green roofs offer a variety of co-benefits beyond stormwater management. In urban centers they are often constructed to accommodate a roof terrace or amenity space. In this scenario, the direct stormwater capture benefit is restricted to the areas with vegetation planted. Another increasingly popular use for rooftop space is for urban farming. Again, the direct stormwater capture benefit is restricted to the areas with planters. To maximize the utility of a green roof as a low impact development tool, coverage with planting should be maximized. In many cases this means only inaccessible spaces are used.

Amenity[edit]

Roof gardens with a high proportion of impermeable surface are popular in high rise developments. These amenity terraces are often described as green roofs, but the LID benefit applies only to the vegetated areas. The stormwater benefit of all kinds of green roofs is maximized by combined with rainwater harvesting for subsequent irrigation. Sedum and native species have all been shown to thrive with daily irrigation to saturation[1].

Rooftop farming is also becoming common in some Ontario cities. Again consideration should be given to the proportion of the roof actually planted. Where large open expanses of roof are being cropped, measures may be required to reduce erosion of exposed planting medium. Any digging or furrows will reduce the stormwater benefit.

Biodiversity[edit]

Biodiversity opportunities are optimized by planting a variety of species. General advice on this has been prepared by the City of Toronto[2]. In the long term, the richness of species increases owing to 'volunteer species'. The desirability of this diversity varies with the aesthetic concerns of the green roof owner.

Design[edit]

The vegetation on this extensive green roof is designed to withstand the deep shade of being in downtown Toronto.

Roof[edit]

Flat roofs should be graded without depressions, with positive drainage ≥ 2% (1:50) towards roof drains. For roofs with pitch greater than 10 % (1:10) additional geo grid or cellular components should be included in the design. These structures reduce the flow rate of the draining water, and help to stabilize green roof components. Green roofs can be installed on slopes greater than 20 % (1:5), but specialized design advice should be sought for the addition of components required to secure the green roof in place. Extensive green roofs do not require additional insulation layers. The underlying roof may be of warm, cold or inverted design. Extensive green roofs add load of around 70 - 300 kg/m2. A structural engineer should be consulted during design to account for the distributed loads including snow accumulation and live loads including maintenance staff. Roof membranes should be waterproof, root resistant, resilient to temperature change, and comply with appropriate CGSB standards as specified in the Ontario Building Code. In most cases a new roof with a modern membrane will not require a separate root penetration barrier. In retrofit scenarios an additional root barrier may be recommended to protect an older roof membrane.

Drainage Layer[edit]

The underlying drainage layer is most often a preformed plastic sheet, formed to include depressions for water storage and perforations to drain excess water. This design has the advantage of being most lightweight, but has minimal impact on flow rates once the water has percolated onto the roof membrane below. An alternative drainage layer solution is to use a granular medium to increase the tortuosity of the flow path and slow peak flow rates.

Filter Layer[edit]

The geotextile layer is included to prevent migration of the planting medium into the drainage layer. Current advice is to specify a free draining textile to prevent potential water-logging of the planting medium. Observations green roof assemblies have shown a reduction of flow from specifications owing to interactions of medium particles with the textile.

Growing Medium[edit]

The green roof media used in Ontario can be classed according to proportion of composted biological material. Some existing installations use materials which comply with FLL guidelines, whilst others use a much higher proportion of compost[3].

ASTM International have a number of standards relating to various design considerations for green roofs. These standards provide good technical advice on the testing of systems and components. Of particular note are:

  • Standard Test Method for Maximum Media Density for Dead Load Analysis of Vegetative (Green) Roof SystemsE2399, and
  • Test Method for Saturated Water Permeability of Granular Drainage Media E2396.

When these tests are completed, the results should be interpreted in relation to the objectives of the green roof. A product complying with overseas guidelines may not serve the needs of a green roof installed in Ontario. In particular, the FLL guide recommends green roof media specifications which may not provide optimal stormwater management or vegetation in our region.

In many proprietary systems the default option for planting medium will be a granular material with very low organic matter content. However, many companies can arrange for a high organic matter alternative to be substituted if requested.

Increasing the depth of planting medium from 10 cm to 15 cm has been shown to benefit the vegetation [4], however stormwater retention was not improved with this increase in depth [5]

Considerations for using a 'high organic', compost based planting medium
Benefits Disadvantages
  • Increased water holding capacity, which benefits both vegetation health and stormwater retention
  • Lighter weight, even when saturated
  • Increased phosphorus concentration in runoff water.
  • The lightweight material is more prone to wind erosion, and this should be accounted for in the initial design, alternatives include erosion control blankets, soil tackifiers, or Sedum mats.

Irrigation[edit]

Regular irrigation has been shown to substantially reduce the stormwater capture benefit of an extensive green roof[6]. One way to reduce the irrigation used on green roofs is through the use of smart technologies. Responsive sensors that suppress irrigation after a rainstorm are routinely attached to green roofs to conserve water. Improvements can be made by instead using a 'soil' moisture sensor to trigger irrigation. State-of-the-art management systems now use predicted weather data to suppress irrigation ahead of storm events, see digital technologies. Due to their limited water retention capacity, many green roofs are coupled with a rainwater harvesting cistern, to capture the excess water. It then becomes desirable to use as much harvested water to regain the cistern capacity, Green roofs can be irrigated to saturation daily throughout the growing season without damaging the vegetation.

Irrigation technology Benefits Disadvantages
Spray Maximizes evaporation Requires higher water quality
Drip or capillary Harvested rainwater is readily used without further treatment
Uses less water		 Planting medium does not 'wick' water sideways readily, so can lead to localized dry areas

Maximizing evaporation with spray irrigation is the faster way to empty a stormwater cistern, and provides some cooling benefit for the building and it's surroundings.

Planting[edit]

The choice of vegetation on an extensive green roof is insignificant in stormwater management compared to the choice of planting medium or the provision of irrigation. The vegetation should be selected to be resilient to both very wet and very dry periods.Sedum species are the most common choice, demonstrating excellent longevity in systems with or without irrigation. Some projects expect the low growing Sedum to remain in graphic designs according to species and flower color. This is not a realistic expectation without significant maintenance costs. Instead project stakeholders should be prepared early in the design process to embrace the green roof as a living and evolving ecosystem. Designs which incorporate both Sedum and native species can help with this.

Drains and vegetation free zones[edit]

Vegetation free areas are often required around the perimeter of the roof to reduce wind uplift, on larger areas requiring firebreaks, for access paths and around drains. To prevent accumulation of sediment and migration of the vegetation, the vegetation free areas should not be filled with decorative aggregate or river rock. Instead concrete pavers or other surfaces that do not actively trap particles will reduce weeding maintenance.

Design for ease of maintenance[edit]

The primary operational concern for operating a green roof is the development of a leak. Green roofs protect the roof membrane from UV damage and should increase the lifespan of the roof. However, in the event that a leak is discovered a section of green roof would have to be removed for access. Some proprietary systems appear to be easier to remove and replace. This may come at a cost, as the rainwater retention of the system is somewhat reliant on continuous coverage of the green roof surface.

Green roofs should receive as little maintenance as possible. Regular inspection is only required to see that the drains are free from obstruction and that the vegetation coverage is adequate to prevent wind erosion. During detailed design, all areas adjacent to the green roof itself should be kept free from granular material. Sediment accumulates in gravel edging, which then permits the vegetation to take root and spread.

  • Example of gravel edging around a roof, which needs weeding.

  • Example of gravel edging around a roof drain, which needs weeding.

  • The amenity value of this roof is enhanced by the tall and climbing plants screening the high safety fences.

  • Very light maintenance has permitted a stand of Mullein to develop on this prairie style green roof, increasing the biodiversity value.

Green roof plants[edit]

Sortable table, click on header you wish to select your green roof plants by
Scientific name Common name Soil Moisture

1=Dry 2=Med 3=Wet

Partial shade tolerance Colour
Achillea millefolium Yarrow 1-2 O
Allium schonaprasum Chives 2-3 1
Aquilegia canadensis Wild columbine 1-3 Y 1
Calendula sp. Marigold 2 2
Carex sp. Sedge 3 Y O
Centaurea sp. Bluet 1-2 3
Coreopsis grandiflora 'Early sunrise' Large-flowered tickseed 1-2 2
Coreopsis lanceolata Lanceleaf coreopsis 1-2 2
Coreopsis tripteris Tickseed 1-2 2
Cosmos sp. Cosmos 1-3 1
Equisetum hymale Rough horsetail 2-3 Y O
Erysimum sp. Wallflower 1-2 1
Geranium maculatum Wild geranium 2 Y 1
Geranium psilostemon 'Rozanne' Cranesbill Geranium 2-3 Y 3
Leucanthemum superbum Shasta daisy 1-2 2
Liatris spicata Blazing star 2 3
Lobelia siphilitica Blue cardinal flower 2-3 Y 3
Lolium multiflorum Ryegrass 1-3 Y O
Lupinus polyphyllus Large leaf lupin 1-3 Y 3
Monarda fistulosa Bee balm 1-3 1
Monarda punctata Horsemint 2 3
Panicum virgatum Switchgrass 1-3 O
Papaver rhoeas Corn poppy 1-3 1
Penstemon digitalis White Beardtongue 1-2 O
Pycnanthemum tenuifolium Narrowleaf mountain mint 1-2 Y O
Rudbeckia hirta blackeyed Susan 1-3 Y 2
Rudbeckia nitida 'Herbstsonne' Cutleaf coneflower 2 Y 2
Rudbeckia laciniata 'Goldquelle' Golden glow coneflower 2 Y 2
Saponaria officinalis Soapwort 2-3 Y O
Schizachyrium scoparium Little Bluestem 2 O
Sedum sp. Stonecrop 1-3 O
Sempervivum sp. Houseleek 1-2 O
Silene sp. Campion 1-2 Y O
Symphyotrichum novae-angliae New England Aster 2 3
Trifolium repens White clover 3 O

Aesthetics of the planting should consider that the practice may be viewed from above.

Construction[edit]

Refer to the Green roof construction page for detailed guidance on construction best practices.

Inspection and maintenance[edit]

Green roof maintenance is typically greatest in the first two years as plants are becoming established. Vegetation should be monitored to ensure dense coverage becomes established. A warranty on the vegetation should be included in the construction contract. Regular operation of a green roof includes:

  • Irrigation System: Watering should be based on actual soil moisture conditions as plants are designed to be drought tolerant. High soil moisture from unnecessary watering will reduce the runoff reduction benefits of the green roof.
  • Leak Detection: Electronic leak detection is recommended. This system, also used with traditional roofs, must be installed prior to the green roof. Particular attention to leak detection should be paid in the first few months following installation (The Folsom Group, 2004).

Ongoing maintenance should occur at least twice per year (Magco, 2003) and should include:

  • Weeding: Remove volunteer seedlings of trees and shrubs. Extensive green roofs are not designed for the weight of these plants, and the woody roots can damage the waterproofing.
  • Debris and Dead Vegetation Removal: Debris and bird feces should be removed periodically. In particular, the overflow conveyance system should be kept clear.


Take a look at the Inspection and Maintenance: Green Roofs page by clicking below for further details about proper inspection and maintenance practices:

Green roofs cover page.PNG

Life cycle costs[edit]

To learn about Life Cycle Costs associated with this practice (i.e. Pre-construction, Excavation, Materials & Installation, Project Management, Overhead, Inspection and Maintenance, Rehabilitation and other associated costs), visit the Green Roof: Life Cycle Costs page to view a cost estimate for an extensive pre-grown mat green roof. Alternatively you can use the STEP's Low Impact Development Life Cycle Costing Tool (LID LCCT) to generate cost estimates customized to your own LID stormwater design project specifications.

Take a look at the Green Roof: Life Cycle Costs page by clicking below for further details:

Construction Breakdown GreenRoof No Infil.PNG

Performance[edit]

Recently laid Sedum mats on a ground level podium roof.
Detail showing the early root development through the mat to the granular planting medium.
Ability of green roofs to meet SWM objectives
Water balance benefit Water quality improvement Erosion control benefit
Partial: Through interception and evapotranspiration No: Green roof runoff may contain elevated concentrations of some contaminants, particularly dissolved Phosphorus, Nitrogen and Heavy metals. Partial: Through interception and evapotranspiration

Water Balance[edit]

Green roofs are primarily a practice used to partially achieve water balance and erosion control objectives through interception and evapotranspiration of precipitation that falls on the roof. The key hydrologic benefit which green roofs have over other forms of LID is the proportion of the water returned to the atmosphere through evapotranspiration. Considerable research has been conducted in recent years to define the runoff reduction or water retention capacity of extensive green roofs in climates similar to those that occur in Ontario and Canada.

  • Controlled studies have indicated that maturing green roofs may have improved water retention properties [7].
  • In Southern Ontario rainwater retention of extensive green roofs without irrigation is between 57% and 70%[8] [9] [6].
  • Including winter periods with snow accumulation and thaw, the annual retention of extensive green roofs is around 50% [9][6].
  • Using a compost based planting medium improves retention by around 10% (i.e., 60% for compost compared to 50% for granular).
  • Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)[6]. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida[10]. The research team modelled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.

An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 [11] [6].

In a study to investigate how green roof runoff reduction performance is affected by climate, Talebi et al. (2019) used water balance and evapotranspiration models to simulate runoff produced by green roofs in six Canadian cities (Vancouver, Calgary, Regina, Toronto, London and Halifax). Results showed that predicted runoff reduction performance varied from 17% to 50% for low water use plants. The best performance was predicted to occur in Regina and Calgary (drier climates), while the poorest performance was predicted for Halifax and Vancouver (wetter climates). Average annual runoff reduction was highest in Toronto and London and lowest in Vancouver.[12]

Water Quality[edit]

Many green roofs receive only rainwater, which is relatively free of contaminants like nutrients and heavy metals, but can contribute contaminants to roof runoff, most notably through leaching of dissolved Nutrients and Heavy metals from the growing medium substrate during early establishment.[13] [14] Concentrations of Total Phosphorus in green roof runoff have been observed to vary from 0.4 mg/L to over 10 mg/L.[15]. Such concentrations are well above the Ontario Provincial Water Quality Objective of 0.03 mg/L for Total Phosphorus (OMOEE, 1994[16]) to control excessive plant growth in rivers and streams. To improve the quality of runoff from green roofs, Vijayaraghavan et al. (2018) recommend considering the sorption capacity of the growing medium substrate, the phytoremediation potential of plants, and incorporation of sorbent Additives to growing medium substrates.[17]

In dense urban centres, green roofs are increasingly being used to receive irrigation from harvested rainwater. Current Ontario Building Code permits the use of rooftop runoff for landscape irrigation purposes, so long as it is 'free of solids'. A 'closed loop' system can be created by coupling a rainwater harvesting system with a green roof and harvesting and reusing roof runoff as a source of water for irrigation during dry periods, so the only water leaving the system is through evapotranspiration. This can prevent runoff from leaving the site and thereby prevent contaminant loading to the environment.

Total phosphorous concentrations reported in green roof runoff(abstracted from Hill 2017)

Incentives and credits[edit]

In Ontario[edit]

City of Toronto updated their Eco-roof incentive program in 2017. It now includes grants for green roof and cool roof structural assessments and is available to non-profit organizations.[18]

LEED BD + C v.4[edit]

LEED offer a relatively large number of points for green roofs compared to other LID technologies.
Sustainable Sites: Open space (1 point)
This credit applies to accessible green roofs on tall buildings with little other outdoor space.
Sustainable Sites: site development - protect or restore habitat (up to 2 points)
This credit applies to green roofs planted with 'native and adapted vegetation' on tall buildings with little other outdoor space
Sustainable Sites: Heat island reduction (up to 2 points)
Green roofs are weighted as effectively as 'High-Reflectance' roofs in a simple calculation to determine the credit.

Sustainable sites: Rainwater management (up to 3 points)

  • Two points (or 1 point for Healthcare) will be awarded if the project manages "the runoff from the developed site for the 95th percentile of regional or local rainfall events."
  • Three points (or 2 points for Healthcare) will be awarded if the project manages "the runoff from the developed site for the 98th percentile of regional or local rainfall events."

OR

  • For zero-lot-line projects only, 3 points (or 2 points for Healthcare) will be awarded if the project manages "the runoff from the developed site for the 85th percentile of regional or local rainfall events."

External links[edit]

Proprietary systems[edit]

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

Green roofs gallery[edit]

  • Pond Road residence at York University, Toronto ON

  • Earth Rangers, Vaughan ON

  • A green roof at Lakeside Park, Mississauga ON.

References[edit]

  1. ↑ University of Toronto. 2017. gritlab. https://grit.daniels.utoronto.ca/
  2. ↑ City of Toronto. 2017. Biodiverse Green Roofs. https://www.toronto.ca/city-government/planning-development/official-plan-guidelines/green-roofs/biodiverse-green-roofs/
  3. ↑ Hill, J., Drake, J., and Sleep, B. (2016). “Comparisons of extensive green roof media in Southern Ontario.” Ecological Engineering, Elsevier B.V., 94, 418–426. https://www.sciencedirect.com/science/article/abs/pii/S0925857416302804?via%3Dihub
  4. ↑ MacIvor JS, Margolis L, Puncher CL, Carver Matthews BJ. Decoupling factors affecting plant diversity and cover on extensive green roofs. J Environ Manage. 2013;130:297-305. https://www.sciencedirect.com/science/article/abs/pii/S0301479713006051?via%3Dihub
  5. ↑ Hill, J., Drake, A. P. J., Sleep, B., and Margolis, L. (2017). “Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology.” Journal of Hydrologic Engineering. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29HE.1943-5584.0001534
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Hill J, Drake J, Sleep B, Margolis L. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. doi:10.1061/(ASCE)HE.1943-5584.0001534
  7. ↑ De-Ville, S., Menon, M., Jia, X., Reed, G., Stovin, V. 2017. The impact of green roof ageing on substrate characteristics and hydrological performance. Journal of Hydrology. Volume 547. pp 332-344. https://doi.org/10.1016/j.jhydrol.2017.02.006.
  8. ↑ Liu, M. Minor, J. 2005. Performance evaluation of an extensive green roof. National Research Council of Canada. NRCC-48204 https://sustainabletechnologies.ca/app/uploads/2013/03/NRC_EastviewGRrept.pdf
  9. ↑ 9.0 9.1 Van Seters, T., Rocha, L., Smith, D., MacMillan, G. 2009. Evaluation of Green Roofs for Runoff Retention, Runoff Quality, and Leachability, Vol. 44 (1): 33 - 47 (2009). Innovative Approaches to Stormwater Management in Canada https://sustainabletechnologies.ca/app/uploads/2013/03/WaterQualResearchJournalCanada_YorkU-Greenroof.pdf
  10. ↑ Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914
  11. ↑ Fassman-Beck, E., Hunt, W., P.E. Robert Berghage, R., Donald Carpenter, D., Kurtz, T., Stovin, V., Wadzuk, B. 2016. Curve Number and Runoff Coefficients for Extensive Living Roofs. Journal of Hydrologic Engineering. Vol.21. Issue 3. ASCE. https://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001318
  12. ↑ Talebi, A., Bagg, S., Sleep, B.S., O'Carroll, D.M. 2019. Water retention performance of green roof technology: A comparison of Canadian climates. Ecological Engineering, 126, (2019), 1-15. https://www.sciencedirect.com/science/article/abs/pii/S0925857418303835?via%3Dihub
  13. ↑ Hathaway, A.M., Hunt, W.F., Jennings, G.D. 2008. A field study of green roof hydrologic and water quality performance. Transactions of the ASABE. Vol. 51 (1) pp. 1-8. https://elibrary.asabe.org/abstract.asp?aid=24225
  14. ↑ Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub
  15. ↑ Hill J., Drake J., Sleep B., Margolis L. 2017. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29HE.1943-5584.0001534
  16. ↑ Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.
  17. ↑ Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub
  18. ↑ City of Toronto. 2017. Eco-roof Incentive Program. https://www.toronto.ca/services-payments/water-environment/environmental-grants-incentives/green-your-roof/

Filter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

Includes the protection of soil from dislocation by water, wind or other agents.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

Tank used to store rainwater (typically roof runoff) for later use.

Abiotic transfer of water vapour to the atmosphere.

A biological community, including humans and their natural environment.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

Stormwater Management

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Includes the protection of soil from dislocation by water, wind or other agents.

The interception, storage and eventual evaporation of rainfall from vegetation canopies.

The quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/day

The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

Any form of rain or snow.

Decayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

A body of water smaller than a lake, often artificially formed.

Relating to the properties, distribution and effects of water on and below the earth’s surface, and in the atmosphere.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Tank used to store rainwater (typically roof runoff) for later use.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

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