− | Green roof performance has not been reported to reduce over time. Controlled studies have instead indicated that maturing green roofs may have improved water retention properties [http://www.sciencedirect.com/science/article/pii/S0022169417300768]. | + | Green roof performance has not been reported to reduce over time. Controlled studies have instead indicated that maturing green roofs may have improved water retention properties <ref>http://www.sciencedirect.com/science/article/pii/S0022169417300768</ref>. |