Green roofs

August 8, 2009 at 6:05 pm | Posted in Green roofs, Plants, Sedum | Leave a comment
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greenroofGreen roofs aren’t new; they’ve been around for eons as people all over the world used natural materials to build their homes.  Only now, green roof design has evolved to be not only a way of protecting a building from the elements, it’s a source of beauty and also an ecological response to the climatic changes we are starting to experience on our little planet.  To survive and thrive on a green roof, a plant needs to be drought tolerant, but also capable of soaking up huge amounts of periodic inundation such as torrential rainstorms to release it slowly after the rain has stopped; be able to withstand temperatures over 40 degrees Celsius and under -40, as well as high winds, snow and ice buildup, and full sun.  The advantages of Sedum are obvious as these tough plants can outperform any other, as well as having pollen and nectar for a wide variety of insects including butterflies, native bees, wasps and other pollinators and predatory insects.  Just watch any patch of Sedum in full bloom and count the visitors.  Mixed Sedum varieties used on green roofs will bloom in succession for a long time, throughout most of the summer and fall.  Given all these positive characteristics, is there any downside?  Some Sedum species are prone to dieback, and if used alone on a green roof, could leave bare patches.  However, if several species and varieties are used, this will just leave a gap for another variety to fill in.  Even on very thin lean soil, Sedum can create an impressive cover, protecting the roof membrane and lowering the temperature inside the building significantly, while at the same time insulating it from low winter temperatures.  This will mean that air conditioning and heating costs will be lower in a building that has a green roof.  In fact, in Toronto, it’s now mandated that a percentage of all new construction will have green roofs.  What will this mean in the long term?  Look at many cities in Europe where green roofs have been utilized for many years as a heat reduction tool.  Cities can become much more livable with more green space, whether on a roof, as a park or over a parking garage to mitigate storm water runoff. Humans have an atavistic need for beauty, and green roofs – or should we call them colourful roofs? – give us that.  Imagine a whole city, roofed in beauty that attracts and feeds wildlife, as well as giving all the benefits of a garden floating in air.  Now that’s a concept we can all live with!

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