If the mayor has his way, all new buildings in Auckland will be required to have a green roof.
The Draft Auckland Plan called for every new commercial building to have a green roof. However, the exact definition of what constitutes a “green” roof is likely to have escaped many living within the city’s boundary thus far. While common in Europe and, increasingly, high-density cities in Northern America, New Zealand’s proliferation of space — green and otherwise — has seen our cities sprawl rather than consolidate their geography.
It’s clear from the content of the plan that this is about to change. We’re going up; we’re getting dense, and we’re pulling those empty lots, former wastelands and disused parking lots into use. The goal, of course, is not a Sao Paolo-style concrete jungle, but low-impact development.
Green, living, or planted roofs are, in theory, exactly the same as green walls, but on a horizontal plane. Their main point of difference is that they can be used to control a staggering amount of stormwater runoff, an issue in our rainy country that affects our beaches, harbours and sewers, and the overall water quality of our rivers and sea.
Specialists Stormwater 360 say a living roof, when correctly managed, can absorb up to 80 per cent of the water that falls on it. “If you have that on a lot of roofs, it reduces stormwater immediately,” says director Greg Yeoman. While his remit is to treat stormwater before it enters the harbour, the other problem is sheer volume: too much rain can mean overflowing sewage systems: “And that’s what closes the beaches.”
Landcare Research’s Robyn Simcock ran Auckland University’s study on the benefits of living roofs. She also has one on top of her garage at home. “I could have a water storage tank, but let’s face it, these are so much nicer to look at.”
Apparently, our European ancestors had one up on us — they used sod roofs for insulation for centuries. “Many modern green roofs were mistakes,” says Simcock. “In Germany the bitumen they used for waterproofing could catch alight, so they put sand down, and then plants grew — so most roofs are based on German technology.”
The plants best suited to the exposed, windy roof environment tend to be hardy, low-lying and low-maintenance ones that are happy in 10cm of soil or less — more soil or growing media, and the roof gets heavy. “Basically, we put plants in, didn’t water them, and saw what survived,” says Simcock.
They also work from a commercial perspective, she says. “There are so many cities in the world where it’s compulsory, so we’re only just getting into it. Once a building is over a few stories tall, cost for a green roof is not too great.”
It could also raise rental and building values, says Yeoman. “Say you’re staying at a hotel or in an apartment, and when you look down rather than a black roof membrane there’s a nice planted area?”
Main pic: Getty image Below: The green roof at The
University of Auckland. Below bottom: The green roof on the NZI Centre, Viaduct