A blue roof is a water retention system installed on flat or low-slope roofs that temporarily stores rainwater to reduce stormwater runoff and lower building temperatures through evaporative cooling. The system uses shallow pools or retention trays that hold water during rainfall events, releasing it slowly through controlled drainage or allowing it to evaporate, which cools the roof surface and surrounding air.
Technical Details
Blue roofs typically retain 40-100 mm of water depth, with drainage rates of 5-10 liters per square meter per hour. The system requires a waterproof membrane, detention layer, and overflow management. Studies show roof surface temperatures can drop 5-10°C compared to standard roofs due to evaporative cooling effects.
Environmental and Practical Benefits
Blue roofs reduce stormwater runoff by 50-90 percent, decreasing strain on municipal drainage systems. They also lower urban heat island effect and reduce building cooling loads. Installation costs range from $15-25 per square meter, making them cost-effective compared to traditional green roofs while requiring less maintenance.