Making green roofs greener

UBC researchers Kasun Hewage and Fabricio Bianchini are taking a good idea and making it better, perhaps spawning a new construction technology for use in arid countries worldwide.

Hewage, an assistant professor of project and construction management in the School of Engineering at UBC Okanagan,   and his Master of Applied Science student Bianchini have been looking at ways to make green roofs even more environmentally friendly by using construction waste.

Green roofs—where plants are grown on specially designed matting that is placed on top of a building—are no longer a novel idea.

But there is room for improvement, and Hewage and Bianchini are looking at recycling waste building materials to form the base layers of a green roof. Currently, materials for the layers are made out of plastic. While the lifespan of a manufactured green roof is about 50 years, it takes 25 years to compensate for the environmental damage caused from making the plastics contained in the roof layering material.

Hewage and Bianchini are searching for the best type of construction waste to reduce the amount of plastic used in green-roof material. Utilizing construction waste also reduces the amount of material that is dumped in local landfills.

Green construction is becoming a mantra throughout North America, and Bianchini says green roofs can play a role in reducing harm to the environment in several capacities. Green roofs act as an insulator, meaning less energy is needed to heat a building in the winter and cool it in the summer.

“Plants regulate temperatures on Earth, so we are trying to apply that to buildings,” said Bianchini.

But finding the best material is not the only challenge they face.

Hewage says the material must not be too heavy —plastic is light, thus making it a popular material—and it must not be too expensive to integrate into a building.

Construction projects produce many types of waste virtually from day one. Hewage says once a type of waste is identified as the optimum material, it can be stored and used at the end of the construction project for green roof applications. The project began last year, and Bianchini is monitoring several green-roof plant beds on campus that were donated by green-roof manufacturing company Xeroflor, which has taken an active interest in the project.  Bianchini will compare the results of the manufactured material against a green roof he constructed using discarded, crushed concrete as drainage material.


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