The Green Roof at MEC

No, people in Canada do not actually leave their doors unlocked all the time. Only during the annual Doors Open Toronto event, where about 150 buildings in the city offer free access to the public. The idea behind the project is to get a chance to look inside some buildings you would otherwise never go and learn something about the architecture or functionality of the building. This year the program had a green theme. I visited Mountain Equipment Co-op, which led fifteen-minute tours through the stockroom, up a ladder, and out of a trapdoor to the green roof.

What was so special about the roof? It’s green! Not painted green, but a “green roof” in the environmental sense. The roof on top of the MEC store holds 75% of rain water, so it reduces the amount of dirty run-off water that eventually ends up in the lake. According to our tour guide, if every building in the city had a green roof, the lake would always be clean enough to swim in. (I assume it’s calculated based on how much rain would be retained by the total flat roof area of the city, but we didn’t get any more details on the numbers.) The roof is also much cooler in summer than regular roofs (about 30 degrees celcius versus 50-60), which reduces the need for energy otherwise used for cooling.

The roof is almost entirely maintenance-free. Twice a year an “Ecoman” comes by to check if no harmful plants have popped up: the roof can’t support a tree, for example, but the big green plant you see in the first picture is an anomaly that has been allowed to stay. There is also an automatic watering system that waters the plants for about 20 minutes if it gets very dry. The sprinklers are coupled to a detector that measures the moisture of the soil. Last summer it went on twice, and it hasn’t been switched on this year at all. So basically, the roof supports itself.

We were also shown what the plants grow on (second picture). They’re on a very lightweight base, and any excess water is collected on a sheet and in a drain.

The City of Toronto Green Roof website has a list of some other green roofs in the city.

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