Green Roofs: A primer

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The things we do for this gig. We write a lot about green roofs, and when invited to help in the installation of one, we couldn't say no and call ourselves treehuggers. Toronto intern Architect Carolyn Moss of Moss Sund Inc. designed the off-grid Harmony Dawn Retreat to have a green roof over the yoga studio (at left in picture). About 30 volunteers showed up to learn about them in a truly hands-on experience. Click on pictures to enlarge.

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The challenge in the design of a green roof is to keep the water flowing. If the drains get clogged with soil the roof can fail from overloading at worst and the plants can't thrive.

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Carolyn chose a modular decking that clicked together as the drainage layer. We thought it a very elaborate system (Windi by Pontarolo Engineering )and it turns out to be a concrete form system adapted for green roofs by drilling it full of holes.

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we filled the legs with gravel to support the filter cloth and retain water, swept it clean, ready for installation of the soil.

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Stephen Peck is President of Green Roofs for Healthy Cities, an organization whose "mission is to increase the awareness of the economic, social, and environmental benefits of green roof infrastructure across North America and rapidly advance the development of the market for green roof products and services." He just returned from the World Green Roof Congress in Basel, Switzerland with all of the latest ideas and information, so he looked at Carolyn's planting plan (squares of sod) and had some suggestions. He pointed out that even on such a small roof we could encourage biodiversity and a wide range of plant and animal life by a)varying the depth of the soil and b)the organic content of the soil.

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The new plan had berms, mounds, gravelly areas vs areas rich in organics, with a few rotting logs thrown in. (and careful monitoring by Carolyn to ensure that the heavy bits were near walls or over beams)

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Crews set to work mixing different soil mixes;

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a bucket brigade transported the soil to the roof. (Standing between Greenroof Staffer Jennifer Sprout and Architect Carolyn Moss, we wondered if we had the wrong name for this kind of work);


Soil was spread out according to the plan (here, a thin layer, light on organics)

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We spent the rest of the afternoon lifting in the brigade, but soon it was over and we could see the results of our labour:


A brown roof. This treehugger is usually into instant gratification, but we are told by people who actually like gardening that if you add water and wait a couple of weeks, things grow and it turns green. It might even look like this:


We have written before how green roofs are wonderful- they absorb CO2, eliminate heat island effects in cities, keep you cool in summer and just look great. We did not know that it is pretty straightforward to do, not very expensive at $ 10-$12 per square foot, and we had forgotten that playing in dirt is a lot of fun.

::Green Roofs for Healthy Cities and many thanks to Andy and Nicola of ::Harmony Dawn for the opportunity, and to Carolyn Moss of ::Moss Sund Inc.