Shades of Green

Sourced from Canadian Architect

Green roofs have now become a standard green building technology, promoted or required in many municipal regions for stormwater management, thermal cooling, and ecological habitat for pollinator species, such as bees. They are a favourite among designers, policymakers and citizens not only because of this ecological multi-tasking, but also because they transform a vast and underused layer of the city—the roof scape—into a thing of beauty. At the University of Toronto’s Green Roof Innovation Testing Laboratory (GRIT Lab), our mission is to study the relation between material choices and environmental performance.

Simply put, a “green roof” is a constructed vegetative system composed of several layers: waterproof membrane, drainage layer, filter cloth, growing medium, and plants. Some green-roof installations include supplemental irrigation as well. Scientists have penned more than 30,000 papers on green roofs and dozens of green roof research labs conduct research worldwide. Why so many? What do we still have to learn about green roof systems?

The reasons we need extensive and ongoing research into green roof technologies is because there are so many different types of green roof products, materials, configurations and dimensions. Growing media and plants are in most cases locally sourced and therefore tend to vary in terms of soil-plant-climate interactions and performance outcomes relative to the three environmental objectives.

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