‘Mechanics’ of a Green Roof

A special look inside the water-saving strategies of the VanDusen Visitor Centre's petaled green roof

The undulating living roof of the VanDusen Botanical Garden Visitor Centre is secretly an entire waterworks. The building has two rainwater cisterns. Excess water from the roof’s ‘petals’ is collected in the first cistern and conveyed into a drywell. One of the roof’s six petals is inverted, allowing it to collect water and divert it into the second cistern, a 79,000-gallon tank beneath the building. This greywater is filtered and used in toilets and urinals.

 

Although the city required the building’s water and sewer systems to be connected to the city service, the visitor center is also the first Vancouver building in more than 45 years to treat blackwater on-site (using a bioreactor wastewater system from Eco Fluid Systems), a technique also used by the center’s architects at the Centre for Interactive Research on Sustainability at the University of British Columbia.

Specifically, blackwater from toilets and urinals is reclaimed and sent to a bioreactor for treatment, directed to a percolation field, and then returned to the surrounding gardens. Hot water, meanwhile, is provided by a biomass boiler fed by dry wood-waste reclaimed from the surrounding area. This off-the-grid water system makes the building completely net zero.