Evaluation of a Residential Green Roof System for Stormwater Runoff Retention

While much green roof research has been directed towards commercial and industrial buildings,
less is known about the sloped roofs of residential buildings. The purpose of this study was to
evaluate a pitched residential green roof system and determine its ability to retain stormwater
runoff. In order to do this, 18 shingled roof models were constructed on three slope angles – 1°,
20° (5/12 pitch), and 40° (10/12 pitch) of which 9 were randomly fitted with a modular green
roof system across three replications. The 42.1% mean stormwater runoff retention for the green
roof systems of was significantly greater than the 18.3% for shingled roof decks. A residential
product (Steep Paks®) performed within the conventional range of previous stormwater retention
studies. The residential green roofs effectively reduced stormwater runoff during periods of light
precipitation compared to periods of heavy precipitation. No difference was found in percent
stormwater runoff retention between the three residential green roof slope angles.