In the United States green roofs and green walls are spreading throughout many of the urban cities with Chicago, San Francisco and Maryland leading the way. This trend first started in Europe where Germany in 2002 had 10% of all its flat roofs covered in vegetation. Japan has also become a leader in facade greening in high-rise urban cores where the exterior wall area greatly exceeds the roof area.
There are many reasons for this interest, both economic and environmental. By effectively replacing hard surfaces, vegetated roofs and walls reduce the urban heat-island effect, making cities more comfortable and buildings easier to cool. The added layer of insulation lessens building heating and cooling loads in some cases. Vegetation also cools via evapotranspiration: The plants and growing medium hold water, which absorbs heat as it evaporates from the ground or is released by the leaves, cooling the air in the process. Plants absorb noise, trap dust, consume carbon dioxide, and produce oxygen. With proper design, plants can protect-and even extend the useful life of-the architectural surface beneath. They reduce or eliminate rainwater runoff, improving the water quality in rivers and streams and decreasing the danger of flooding. Vegetated surfaces provide a habitat for birds and other creatures, enhancing urban biodiversity. They can also become usable, enjoyable, harvestable gardens for humans, while improving the cityscape as viewed from high-rises above. You can read more about these verdant surfaces here.
Green roofs are just starting to catch on in New Zealand with companies like Green Roofs LTD and Living Roofs promoting the uptake of green roofs in New Zealand.
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