We recently installed an irrigation system for a three-story green roof in Cincinnati. For two years, the rooftop garden suffered from a lack of water, even with drought-tolerant sedum plantings. Green roofs are a popular landscaping trend that we love, but don’t skip the sprinkler system!
During Summer, Rooftops Are Hot and Dry: Not a Good Garden Environment
The soil on a green roof is a porous type of gravel that uses expanded shale. Regular soil is too heavy for a roof to bear. Frequent and shallow irrigation is important in this environment. The water runs right through the soil, so the best way to apply water is with overhead sprays or rotors. Although we have tried drip irrigation, it seems to drip right through the soil, creating water waste and not supplying water to the plant roots.
Rooftop Irrigation Acts as Air Conditioning for the Room Below
Along with keeping the plants alive, irrigation helps keep the room below the roof cooler in hot months. The sprinkler system puts moisture in the soil, which removes heat during evaporation. This saves on energy costs.