At least 6 bus shelters across the city have sprouted green roofs this week as part of a cute STM marketing campaign.
At least the STM has got something in this vein worth promoting: in 2008 the STM installed a 10,000 square foot green roof atop a new garage built in the Ahuntsic-Cartierville borough.
Green roofs can help insulate a building and provide savings on heating and cooling. Also interesting for a garage, green roofs can help with sound-proofing : by some estimates a 12-cm substrate can reduce noise by 40 decibels. The plant covering can also reduce wear on the structure, although the weight of a green roof (45 lbs per square foot) can be a concern to those who dream of a green roof on an older buildings (in comparison, snow weighs about 15 lbs per cubic foot).
From an environmental perspective, green roofs are absorbent, reducing the amount of rain water that winds up in our combined-sewer sewage treatment system (pretty much all the rain and snow that falls on the island gets the same treatment process as our toilet water). Green roofs also reduce urban heat-island effects and help filter particulate pollution out of the air (again, relevant for a garage). For a ton more information about the qualitative and quantitative benefits of green roofs, see “green roofs for healthy cities.”
Even though I question whether the STM really needs to prove they’re “green”, it will be nice to see a patch of grass in the landscape, even if it’s above our heads. Hm, I wonder what would happen if we tossed in some wildflower seeds?