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A Green Roof
by Hope Bell
A Green Roof
There is a movement afoot to replace shingles with sedums. Although Germany has taken the lead in developing this idea, North Americans are starting to follow suit and investigate the benefits of the combination of gardening and architecture. The idea may have been around since ancient times — think of the hanging gardens of Babylon — but green roofs are finally becoming mainstream in the modern world.
Depending on who you speak with, there can be different definitions of a “rooftop” garden. Some people use the term in reference to terrace or balcony gardens. Some follow a stricter definition of gardens on the actual roof of industrial or other buildings. They are also sometimes referred to as “Green” roofs”, "living roofs" or "eco-roofs”.
Green roofs are attractive, ecologically beneficial and offer several practical advantages to a business or home. It takes experience to know what perennials will perform well in this unique, often extreme microclimate. Studies indicate that Green roofs reduce a homeowner's cooling costs in the summer and the urban "hot-spot" effect that is damaging to the environment. In colder regions like Canada, coniferous species, such as junipers, on a roof can conserve heat and reduce energy consumption in winter. Installations must take into account the weight of materials on the roof, drainage, maintenance and appropriateness of plants selected for the area. Green roofs can be as large or small as the building (or tenant) can handle, but every bit of vegetation in the city will help improve air quality and aesthetics. They can also insulate sound, add recreational space, and increase the longevity of the existing roof by protecting the underlying layers.
According to the Green Roofs for Healthy Cities network, one square metre of uncut grass produces enough oxygen to sustain one person for a year.
A roof is a very different environment from a garden rooted in natural soil at ground level. The choice of plants depends on location, climate, and the purpose of the roof. A hotel on the West coast grows herbs, vegetables, and flowers on its roofs, reducing its food costs and energy consumption. Others with inaccessible roofs sow grass to get good coverage with little maintenance.
Creating a green roof isn’t quite as simple as sowing grass seed on the roof, but it’s not far off. There are various ways to install one, but a few rules apply.
A high-quality water-proofing membrane should be put down over the existing roof. Then a root repellant system, a drainage system, a filter membrane, and a lightweight soil layer go on top of the waterproof membrane.
If it’s not installed properly, the roof might leak so it’s recommended that you consult one of the growing number of certified green roof installers in North America before greening it up.
Green roofs are an extension of the existing roof that allows plant trees and shrubs to grow in a light-weight growing medium.
Green roofs are typically installed on flat roofs, but can be adapted for sloped roofs as well. They can be either "intensive," with about 12 inches of soil and a wide variety of plants, or "extensive," with about 3 inches of soil and a more limited selection of suitable plants. Extensive green roofs are less expensive, lighter, and easier to maintain.
Green roofs in residential areas have been outnumbered by commercial coverage because the task of installing a green roof can be overwhelming for individual home owners. In part this is due to expense but also attributed to a lack of knowledge in general about green roofs, their benefits and how to install them. As an important feature of a home’s structural soundness, the thought of an “outside the norm” roof treatment can be intimidating.
The green roof market is changing to encourage more residential installations and some do-it-yourself modular green roofing systems are now available from companies in Canada. (http://www.eltgreenroofs.com/greenroofs-DIYproducts.html)
Some interesting websites include:
http://www.greenroofs.com/
Greenbacks From Green Roofs: Forging a New Industry in Canada (CMHC) http://www.greenroofs.org/pdf/Greenbacks.pdf
Green Roofs for Healthy Cities http://www.greenroofs.net/index.php
City of Toronto, Green Roof pilot program http://www.toronto.ca/greenroofs/index.htm
Green Grid www.greengridroofs.com
(2007-02-16) |
