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→Design
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=Design=
====Design===
==Planting==
<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 mixture to be prepared if requested. </p>
<p> The benefits of 'high organic mixes' are:
<ol>
<li>Increased water holding capacity, which benefits both vegetation health and stormwater retention, </li>
<li>Often lighter weight, even when saturated, </li>
<li>
<ol>
The disadvantages of a 'high organic' planting medium are:
<ol>
<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>
</ol>
<h4>Planting</h4>
<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>
<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>
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=Performance=
=Performance=
==Water Quantity==
==Water Quantity==