A blue roof is a non-vegetated storage system made of stone and a sealed waterproof roof membrane that allows the roof to retain stormwater. The collected stormwater is then slowly released to roof drains or allowed to evaporate.
![](https://water.phila.gov/pool/images/blue-roof-example-1200x675.jpg)
A blue roof is a non-vegetated storage system designed into a roof, allowing the structure to retain stormwater. It is installed over a sealed roof membrane and typically utilizes check dams, trays, or modified roof drains to capture and temporarily detain or slow stormwater before it reaches downspouts. Stormwater detained by blue roofs is slowly released to the roof drains and/or removed through evaporation, especially during warm, sunny weather. Blue roofs are best suited for buildings with relatively flat roofs and other auxiliary structures.