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→Design
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<h4>Roof</h4>
<p>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. </p>
<p>Extensive green roofs do not require additional insulation layers. The underlying roof may be of warm, cold or inverted design. </p>
<p>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 snow accumulation and live loads including maintenance staff.</p>
<p>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. </p>
<h4>Drainage Layer</h4>
<p>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. </p>
<p>An alternative drainage layer solution is to use a granular medium to increase the tortuosity of the flow path and slow peak flow rates. </p>
<h4>Planting Medium</h4>
<h4>Planting Medium</h4>
<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>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.