Changes

<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>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>

<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>