water usage. In drier climates, blue roofs act as a water conservation tool harvesting the water that falls on a roof's surface and collecting it at a controlled rate. Design compatibility Another major benefit of blue roofs are their ability to work alongside other rooftop systems such as solar panels (both solar thermal and pv), and HVAC mechanical equipment. Some recreational blue roofs integrate rooftop waterplay areas that can also be used to irrigate a green roof, or to cool the roof of a building on hot days, in order to eliminate or at least reduce the HVAC load placed on mechanical refrigeration equipment. Some blue roofs utilize stored water for beneficial on-site purposes cooling of solar panels and irrigation of a green roof. One example of a blue roof that provide ancillary services was the winning entry (First Place, 10,000 Euro prize) in the 2004 Coram Sustainable Design Award, by Steve Mann. Types Active blue roof Active blue roof systems control the rate at which water drains from a rooftop through mechanical means. Sometimes referred to as automated roof runoff management systems, active blue roofs use valve configurations and controls to monitor and regulate the discharge of stormwater runoff from roofs. Water ponded on the roof can be released in several ways, including via a pneumatically or hydraulically actuated pinch valve, an electronically controlled valve connected to a timer, or manually opening the valve. Active blue roofs for stormwater detention using forecast integration were first proposed in 2008. Passive blue roof Passive blue roof systems control the rate at which water drains from a rooftop through non-mechanical means. Unlike active systems which inhibit water flow through drainage pipes, passive systems temporarily detain water on the surface of the roof by lengthening the path the water must take in order to reach outlet drains. Blue roofs can include open water surfaces, storage within or beneath a porous media or modular surface, or below a raised decking surface or cover. Roof‐integrated passive blue roof designs are built to retain water directly on a roof's surface, protected by a waterproof membrane, for extended periods of time. This ponding of water can be done either within a porous media, such as gravel, or free standing on the roof surface. The release rate of the stored water is controlled by weirs on the roof drain. Roof-integrated designs are most effective in new construction as