Tuesday, 27 October 2015

The Shire of London: The Benefits of Green Roofs

While they may invoke images of Hobbits and the Shire, green roofs could be part of the solution to keeping cool in a warming world. The urban heat island effect (urban areas becoming warmer than surrounds due to more pavement) can raise the temperature in the city by 12oC at night and currently affects 54% of the world's population.

Source: Marilyn Novy
The reflectivity (albedo) and latent cooling are what draw people to green roofs, but much of their temperature regulation comes from insulation (Del Barrio, 1998). They are most cost effective for old uninsulated buildings, which make up 50% of the UK's homes and businesses. This reduction in energy for heating and cooling will help mitigate CO2 emissions.

People may argue against this initiative because of the expense (10-14% more for a 60-year roof). However green roofs provide benefits that plain old insulation does not offer. They reduce runoff, cool the outdoor temperature (especially when paired with green walls between close buildings), capture pollutants (notably ozone ), and create easy access to nature. This seems like a lovely way to combine adaptation with an improved lifestyle.

3 comments:

  1. I love the idea of green roofs, definitely make for a better view from your high rise office, as well as (probably more importantly!) encouraging wildlife in urban areas.
    I wonder if you came across anything that argued where to best install green roofs? I was going to make a comment asking if the costs that you mentioned would be offset by the reduction in heating costs, but then it occurred to me that in a more tropical climate the insulating effect of a green roof would actually increase the energy used to cool a building. Is this an adaptation best suited to buildings in more a more temperate climate?

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  2. The insulation aspect of the roof helps keep heat out during the summer and keep heat in during the winter. If you wanted a green roof specifically for a warm climate you'd try to incorporate plants with large leaves that would create shade.

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  3. One thing I worry about, which I didn't find much information on, was how they would work in areas with heavy snow. I know some places in upstate New York and Canada need to worry about shovelling off roofs to avoid building collapse. And shovelling snow off foliage is a lot harder than pavement. But Chicago seems to be doing pretty well with their roof (pictured above) and they get their fair share of snow.

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