Researchers at the University of British Columbia’s Okanagan campus are trying to green up an already green idea.

Professor Kasun Hewage and master’s student Fabricio Bianchini, both engineers, are investigating whether they can improve the environmental footprint of green roofs.

Because they are testing the roofs in a drier climate in the Okanagan than where the roofs are normally used, their research could also help prove the roofs’ usefulness in arid regions throughout the world.

Green roofs have been used for decades in Europe, and have more recently caught on in North America.

There are examples of green roofs in downtown Vancouver, including at the Vancouver Public Library and the Vancouver Convention Centre.

The green roofs have a range of benefits which include absorbing greenhouse gases, lowering temperatures directly above the gardens and reducing run-off.

The green roofs also help filter dust and potentially harmful chemicals, and reduce the heating and cooling loads on buildings.

However, Hewage and Bianchini found the benefits of green roofs are diminished by the pollution created during the manufacture of the plastics and rubber mats that provide drainage for the plants.

The researchers’ life-cycle analysis showed it would take as much as 25 years to compensate for the environmental damage caused from making the plastic in the matting.

Life-cycle analysis is an examination of the environmental effects of a product from cradle-to-grave. The analysis includes the extraction of raw materials, manufacturing and disposal or recycling of materials at the end of the product’s life.

The researchers’ assessment also compared the toxic emissions from the industrial production of the plastic to the air pollution removed by the plants during the lifespan of a green roof.

“The current green roof is not sustainable enough because some of the manufacturing materials themselves emit gases, some toxic materials,” says Hewage.

Once it was known that the mats diminished the benefits of the green roofs, Hewage and Bianchini decided to test the use of construction material waste as a drainage base to replace the plastic mats.

The construction waste is abundant by the time a green roof would be constructed, would produce no additional manufacturing pollution and would also be a unique way to reduce the amount of waste going into landfills.

Hewage twigged to the idea of using building waste such as bricks and concrete during his doctoral research in construction management at the University of Calgary. He had become alarmed about the amount of waste created by construction.

As much as 30 per cent of municipal waste comes from building projects, he said.

Later, his concern was reaffirmed working on oilsands mega-projects, including in Fort McMurray, in northern Alberta.

Hewage and Bianchini have eight test roofs under study at the UBC Okanagan campus.

They are investigating the use of crushed concrete, crushed brick and crushed foam, also known as rigid insulation. They are testing each individually and using several combinations, comparing those to standard green roofs constructed with the plastic mats.

The test roofs are using Sedums, a flowering plant with more than 400 species, that can exchange oxygen and carbon dioxide with little sunlight, allowing the conservation of water under drought conditions. “The use of different types of Sedums allowed us to have plants of different colours that bloom at a different time of the year. This characteristic adds an esthetical value to the green roof,” noted Bianchini.

The researchers are taking numerous measurements including temperature, humidity and water quality.

Water quality is a particularly important measurement because if any chemicals are added to the run-off from the waste construction material that will have a damaging environmental effect, offsetting the benefit of using the waste construction material.

Temperature is important because it relates directly to the energy reduction in cooling and heating a building, added Hewage. “If you need more energy to heat or cool the building, you need more fossil fuels.”

Green roofs have already proven to reduce the costs of heating and cooling buildings.

For example, a study for the City of Chicago suggested there would be $100 million in annual savings from reduced cooling if all of the buildings in Chicago were retrofitted with green roofs, 30 per cent of the total land area.

Chicago has led the way in the use of green roofs in an effort to reduce the so-called urban heat island effect, building an extensive green roof on its city hall a decade ago.

Hewage is excited about the possibility that using waste material to reduce the environmental footprint of green roofs could be used all over the world.

Research shows that what works in Vancouver or Toronto may not necessarily work in more arid climates, so areas with similar climates around the world will benefit from the research being conducted at UBC’s Okanagan campus, says Hewage.

That’s one of the factors that drew Bianchini, a 24-year-old engineer from Costa Rica, to the project. “I wanted to think of an idea that it doesn’t matter the place where you are [doing your research] in order to help the environment. I wanted to make something that I could take back to Costa Rica. Something you can actually make some modifications, but use in other places,” he said.

ghoekstra@vancouversun.com