Greener Roofs: Aerial Imagery Reveals Growth in Toronto

Lush rooftops are levelling up Toronto’s skyline.

STARTER STATS

• Toronto was the first North American city to mandate green roofs in 2009

• Green roofs can lower surface temperatures by as much as 10-20° C

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Researchers from the University of Toronto are using aerial remote sensing to track the health of Toronto’s green roofs, uncovering a cool trend: as the roofs age, their vegetation thrives.

Using high-resolution multispectral images with a resolution down to 7 centimetres per pixel, the team analyzed nearly 1,500 green roofs from 2011 to 2018.

Led by doctoral graduate Wenxi Liao and Professor Sean C. Thomas, their findings show improved vegetation health and less patchiness over time, especially for roofs planted with drought-tolerant sedum. These hardy plants store carbon dioxide at night, reducing water loss and boosting resilience.

“This bird’s-eye view shows green roofs are more than just pretty—they’re a practical fix for urban challenges like flooding and heat."

— Dr. Sean C. Thomas

Not all roofs are equal. Tall buildings and narrow designs face harsher conditions, with high winds and shallow soils stunting plant growth. Still, most green roofs are getting greener. This helps them reduce urban heat islands, curb noise, improve air quality, and provide habitats for birds and insects.

The study could shape smarter green roof designs, making cities more sustainable. Future plans? Tweak designs for high-rise and skinny roofs to keep the green momentum growing.

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