Green roofs, in the form of sod and thatching, have been used around the world since ancient times. Dwellings in Babylon, Scandinavia, Iceland, and Europe, as well as early settlements in the Midwestern United States, used these materials because they were readily available and made homes more comfortable by helping to regulate the temperature and protect against the elements. Today, green roofs are being updated with modern technology and materials to improve their efficiency and have become a major component of sustainable building initiatives.
Green roofs are typically composed of waterproofing, drainage mats, root barriers, specifically formulated planting media, and plants. The depth of the planting media impacts the types of plants that can be used. When less than six inches thick, the system is termed an “extensive” roof garden and will typically use only succulent herbaceous plants. If more than six inches, the system is termed an “intensive” roof garden and allows for the use of a broader plant palette. The planting media layer on this roof is three inches. Either type of roof garden will help cool a building in the summer and insulate it in the winter. Green roofs also slow the rate of runoff and reduce the volume of stormwater entering sewers by up to 80 percent. Additionally, green roofs filter pollutants and carbon dioxide out of the atmosphere, encourage biodiversity, and provide habitat for birds and butterflies. Most green roofs last longer than traditional roofs and they add aesthetic value to buildings and their surroundings.
The use of green roofs is well established in Europe and is increasing in the United States. They can be adapted for commercial or residential use, even on high-rise buildings, and they are suitable for a variety of architectural styles. They can be small in scale, as in a shed roof, or expansive enough for an industrial-sized building. Although they require special structural considerations and are more expensive initially than traditional roofs, they typically pay for themselves with reduced heating, cooling and infrastructure costs.