High meadows

If the mayor has his way, all new build­ings in Auck­land will be re­quired to have a green roof.

Element - - Architecture - By Sam Eich­blatt

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

Basin.

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