Aerial Study Reveals Toronto’s Green Roofs Are Maturing Successfully

Urban Greenery From Above

Researchers from the University of Toronto have conducted what sources indicate is the most comprehensive analysis to date of green roof performance in an urban environment. Using aerial remote sensing technology, the interdisciplinary team tracked vegetation health across nearly 1,500 green roofs in Toronto between 2011 and 2018, according to their study published in Nature Cities.

Urban Greenery From Above
Maturing Green Infrastructure
Advanced Imaging Technology
Toronto’s Green Roof Leadership
Design Factors Affecting Performance
Environmental Benefits Documented
Future Urban Planning Implications

Maturing Green Infrastructure

The report states that Toronto’s green roofs showed overall improvement in vegetation health and reduction in vegetation patchiness as they aged. “Being able to follow the green roofs over time gives us some real insights and guidance on how to do a better job with green roofs,” says Sean C. Thomas, a professor at the Institute of Forestry & Conservation in the Daniels Faculty, according to the research findings.

Analysts suggest the study provides crucial data for urban planners seeking to enhance sustainability in cities worldwide. The research team included lead author Wenxi Liao, a U of T doctoral graduate in forestry conservation and civil engineering, along with researchers from multiple Canadian universities.

Advanced Imaging Technology

The team analyzed multispectral airborne images captured by the City of Toronto that provided extremely high resolution of approximately seven centimeters per pixel. This advanced remote sensing technology enabled detailed assessment of vegetation health across the urban landscape without ground-level inspection.

Toronto’s Green Roof Leadership

Toronto became the first city in North America to implement a green roof bylaw in 2009, requiring new developments larger than 2,000 square meters to dedicate part of their rooftop space to vegetation. The bylaw specifically covers areas designed exclusively for vegetation rather than public access spaces.

Despite challenging conditions including high wind exposure and shallow soils on exposed rooftops, visible and infrared data reportedly showed most green roofs in Toronto are becoming greener over time.

Design Factors Affecting Performance

The study revealed important design considerations for future green roof installations. According to reports, green roofs on top of tall buildings performed significantly worse than those at four stories or lower. Similarly, long and skinny green roof designs tended to experience more degradation.

Most green roofs are planted with low mat-forming species such as sedum due to their extreme drought tolerance, and the analysis suggested that roofs with sedum performed the best. Sedum’s unique carbon storage mechanism helps reduce water loss while supporting photosynthesis.

Environmental Benefits Documented

Researchers highlighted multiple environmental benefits of successful green roof implementation. “With a conventional flat or a slanted roof, water drains quickly off the structure in an extreme rainfall event that can overwhelm infrastructure,” Thomas explained, according to the study. “Green roofs are an effective way of storing water and delaying the peak of the flood event.”

Additional benefits identified include:

Cooling effects that mitigate the urban heat island phenomenon
Reduced noise pollution and improved air quality
Enhanced urban biodiversity through support for insects and birds

Future Urban Planning Implications

The study’s findings reportedly provide valuable guidance for future green roof design and urban sustainability planning. As cities worldwide grapple with climate change and urbanization pressures, the research offers evidence-based insights for improving green infrastructure performance.

The comprehensive aerial imagery analysis establishes a framework that could be applied to other cities seeking to evaluate and improve their green roof initiatives, according to the research team.