Green roofs are roofs that are fully or partially covered with vegetation without pots that grows on impermeable layers of various materials. They can provide insulation, reduce cooling and heating costs, and even help with stormwater management. But before you install a green roof, there are some key considerations to keep in mind. Structural and load-bearing capacity of the building is an important factor to consider when installing a green roof.
You'll also need to think about plant selection, waterproofing, and drainage or water storage systems. Intensive green roofs tend to have slightly greater stormwater volume benefits, but they also have higher installation and maintenance costs and require more structural capacity compared to extensive and semi-intensive green roofs. Leak detection is another important factor to consider when installing a green roof system. Make sure that the system is designed to be compatible with leak detection, as detecting leaks in green roof assemblies that incorporate root barriers is very difficult, if not impossible, in most cases.
The best time to set up a rooftop garden is early spring or early fall so that the plants have time to get established before the ends of summer or winter. When it comes to soil mixes, commercial green roof soil mixes are great if you can find a point of sale, but look for a mix with locally available materials to avoid unnecessary shipping costs. Common plants for green roofs include perennial succulents such as stone crops and chickens and chicks or sedges and groundcovers. Tests immediately after installing the waterproofing make it possible to correct any leaks before installing the green roof.
Even green roofs with underground drip irrigation systems will need sprinkler irrigation until the roots have grown enough to reach the water in the irrigation pipes. The ideal window for planting green roofs in Minnesota is from after the last frost to four weeks before the first frost.
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