Green Roof at Walter Reed CC © by Arlington County

Green roofs are also known as living roofs – these two names may give you an idea of what they involve. In essence green roofs are gardens grown on a roof that can take a diversity of forms and functions. The benefits of green roofs are many; they can help insulate a building leading to a lower electricity bill, uptake carbon, harness rainwater, provide a habitat for insects and birds (especially valuable in a city) and grow food for the building occupants or local community. Vegetation is planted on top of waterproof membrane on the roof of a usually commercial building. There are many reasons for having a green roof and some requirements too.

Compared to traditional roof tiles plants, their roots systems and soil weigh considerably more. For this reason the building needs to be able to structurally support the roof and sometimes retrofitting older structures will not work. Not just because of the weight but because of the need of a drainage system which is an extra layer underneath the vegetation and growing medium.

If the weight of soil garden simply will not work, a different type of green roof is needed- such as a lightweight hydroponic or aeroponic method of growing plants or sedum or succulent plants that requires little soil and little water.

Having a dash of vibrant green brings air and visual qualities that are hard to come by in grey concrete and blue glass jungle environments of modern urban areas. But there are many more advantages than meet the eye: weather buffering, insulation during colder days, water protection in the rain and even temperature control throughout the year. The later point is particularly helpful in combating the phenomenon know as urban heat islands (UHI). UHIs are metropolitan areas which are significantly warmer than rural surroundings, primarily because of urban developments that use heat retaining materials such as concrete and asphalt.

A vegetated roof is better than a mere waterproofed roof because it absorbs water so in heavy downfalls there is reduced runoff. Plants use water in photosynthesis, The green pigments in plants (chlorophyll) also uses carbon dioxide taken from the atmosphere to complete the photosynthesis process.

Green roofs can be seen in many countries around the world, from Scandinavia where sod/turf roofs have been around for centuries, to the UK, Europe, Egypt, USA and Australia.

Modern green roofs are of three main types, intensive, semi-intensive or extensive, the primary difference being in the depth of growth, but hence also in the costs and visual aspects. The upfront investment required for a green roof is one for the future and well worth the benefits which extend to visual and social impact.

Unfortunately regulations and guidelines on building a green roof are currently sparse. Much of today’s green roofs have been developed by an individual’s initiative, an environmentalist, a landscape architect or designer. The activist group in New York, Sustainable South Bronx has also installed green roofs to suit their needs. The oldest regulations were published in Germany in the 1990s, “Guidelines for the planning, execution and upkeep of Green Roof sites” from the Research society in Germany. EU funded research has provided more recent code of best practice developed in England with the support of the Environment Agency. Even so it’s important to note that guidelines and codes of best practice for green roofs are often specific to certain climate regions. Ultimately, thinking through the needs and limitations to a specific roof will yield the best result. Like gardens, no two green roofs need be the same.

There are ongoing research programmes in the area of green roofs allowing plenty of opportunities for academics with green inclinations. Careers in the green roofing business are also on the increase and hopefully will continue especially as the built environment is  Many commercial buildings are topped with green scenes, examples include Canary Wharf in London, Ford’s Motor Company in Michigan, Ballard library in Seattle. There is no glass ceiling to success in the green or sustainability world, but perhaps there’s a green roof?