Friday, 26 January 2018

Questioning green walls

It had to happen sooner or later: green walls are being questioned.  Are they really a good thing from a sustainability point of view?

For anyone who has harboured any thoughts that external green walls on high-rise buildings might be one more expedient combination of sustainability rating 'bling' and marketing hype, a recent post in the Fifth Estate is compulsory reading.

The article quite fairly sets out the issues to be considered.  On the positive side, there is aesthetic value, heating and cooling load reduction, and contribution to mitigating the urban heat island effect.  On the negative side, focus is primarily on the overall cost, both financial and in resources, especially in maintenance. 

Put as simplistically as that makes it sound like negative criticism is short sighted, and another example of the ‘race to the bottom’.  But as usual, the devil is in the details.

First and foremost, the discussion is about a very particular type of green wall – exemplified by the world’s tallest example at One Central Park in downtown Sydney, the iconic high-rise residential tower by Jean Nouvell and Patrick Blanc.  This kind of green wall is effectively a relatively thin ‘veneer’ within the fa├žade – essentially a curtain wall otherwise dominated by glazing.  Notwithstanding the skillful choice of species of plants borrowed from natural cliff-like ecologies, this typology of green wall is inherently fragile and demands high maintenance. The Fifth Estate article hints at the idea that this increased commitment to maintenance might be viewed positively as a contribution to social sustainability – I assume by creating jobs.

But there are other ways of greening buildings. Most obviously, roofs are friendlier surfaces, though the higher the building the smaller the proportion of roof to overall building surface. 

More usefully, facade planting can happen in robust configurations such as bigger planting boxes. We have plenty of precedent for these more traditional artificial landscapes – probably the best known is WOHA's Park Royal complex in Singapore.  Arguably the only barriers to employing them more often, are short-sighted restrictions such as indiscriminately applied floor space ratios.

Ultimately, I agree with Dr Paul Osmond, director of the Sustainable Built Environment Program at UNSW, when he says that the value of green walls over their lifecycle is still an open question:
“From a service life perspective – from design, installation, maintenance, replacement of plants, water systems and even decommissioning – no one has really explored that.”
As usual, I do not try to reproduce the original article. 
You should read it here.

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