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<p> Due to their limited water retention capacity, many green roofs are coupled with a 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.
<table class="table table-responsive table-striped"><tr class = "success"><td>Irrigation technology</td><td>Benefits</td><td>Disadvantages</td></tr><tr><td>Spray</td><td>Maximizes evaporation</td><td>Requires higher [[Water Quality|water quality]] standard. </td></tr><tr><td>Drip or capillary</td><td>Harvested rainwater is readily used without further treatment <br>Uses less water</td><td>Planting medium does not 'wick' water sideways readily, so can lead to localized dry areas</td></tr></table>
→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.]]
[[File:TD Bank.jpg|thumb|The vegetation on this extensive green roof is designed to withstand the deep shade of being in downtown Toronto.]]
<h4>Roof</h4>
<h3>Roof</h3>
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 check dams 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.
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 check dams 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 do not require additional insulation layers. The underlying roof may be of warm, cold or inverted design.
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.
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.
<h4>Drainage Layer</h4>
<h3>Drainage Layer</h3>
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.
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.
An alternative drainage layer solution is to use a granular medium to increase the tortuosity of the flow path and slow peak flow rates.
<h4>Filter Layer</h4>
<h4>Filter Layer</h4>
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.</p>
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.
<h4>Planting Medium</h4>
<h3>Planting Medium</h3>
{{:Green_roof_media}}
{{:Green_roof_media}}
<h4>Irrigation</h4>
<h3>Irrigation</h3>
Regular irrigation has been shown to substantially reduce the stormwater capture benefit of an extensive green roof[http://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001534]. One way to reduce the irrigation used on green roofs is through the use of electronic 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 prevent irrigation ahead of storm events[https://optirtc.com/products].
Regular irrigation has been shown to substantially reduce the stormwater capture benefit of an extensive green roof[http://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001534]. One way to reduce the irrigation used on green roofs is through the use of electronic 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[https://optirtc.com/products].
Due to their limited water retention capacity, many green roofs are coupled with a 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"
|+ Types of Swale
|-
!style="background: darkcyan; color: white"|Irrigation technology
!style="background: darkcyan; color: white"|Benefits
!style="background: darkcyan; color: white"|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.
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.
<h4>Planting</h4>
<h3>Planting</h3>
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. </p>
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 <em>Sedum</em> 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.
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 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.
See: [[Planting for Green Roofs]]
See: [[Planting for Green Roofs]]
<h4> Drains and Vegetation Free zones </h4>
<h3> Drains and Vegetation Free zones </h3>
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.
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.