The Growth of Green Roofs in BC

Reducing cooling costs, mitigating storm water run-off and absorbing carbon are just some reasons why more businesses are setting up green roofs.

With local governments such as the District of Maple Ridge and the City of Port Coquitlam adopting policies to encourage them, green roofs in BC are about to grow more rapidly than ever before.

“BC has the potential to be a leader in green roof design and construction,” states Michelle Nakano, former Chair of the Landscape Design and Installation Program at Kwantlen Polytechnic University. “But to do so, we need to develop systems that perform well in our unique climate, maximizing the economic and social benefits.”

On a 1,400 m2 elevated research platform at BC Institute of Technology’s (BCIT) Centre for Architectural Ecology in Burnaby, researchers analyzed optimal establishment and maintenance techniques, options for shallow-depth systems and the impacts on noise absorption by experimenting with various plant species, propagations, and substrate depths.

Plants behave differently on green roofs because they are grown at higher elevations in mineral mediums (soil is too heavy).  Researchers compared plant cuttings, plugs and pots to determine the optimal propagation type for green roofs in BC. Plant plugs had the best overall coverage with minimal drying out and weed susceptibility.

The ability to successfully implement cost effective shallow-depth systems is critical to further growth of the industry in BC. By experimenting with different plant mixtures at different depths, a selection of BC coastal plants had the most promise, providing adequate coverage at depths as low as 75mm.

Lastly, researchers measured frequency-dependent sound absorption data for various plant species and substrate depths, providing data for further research on the effects on noise pollution.

“Green roofs are a new emerging aspect of our industry, with significantly different growing conditions than the average garden,” states Tim Loewen, Chair of the BC Landscape and Nursery Association.  “This new research has provided key information about optimal establishment techniques as well as how green roofs add another environmental benefit by muffling noise pollution in cities.”

Funding: $108,172 through the federal Canadian Agricultural Adaptation Program. (A0602)

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