Vertical forest 2.0

There must be something in the air.  Well, there is....lots of air pollution in the many cities around the world eating up their hinterlands of agricultural land and forest remnants.  In reaction, we have witnessed an increasing number of projects to reintegrate greenery with buildings at both urban and building scale.

Urban forests can help establish green corridors.  Green roofs can add a bit more vegetation.  But by definition, it is difficult to replace the net surface area of plant material found in natural forests, when so much area is dedicated to roads and other impervious infrastructure, and walls, glazing, PV panels or water harvesting roofs on buildings.

The only chance we have of 'multiplying' the green surface of a given piece of land is to put plants on the vertical facades of buildings.

That thought was given very literal interpretation most famously in Patrick Blanc's green wall at the Museé du quai Branly in Paris, and later at 1 Central Park in Sydney.  Such 'green walls' – and others less famous both before and after – represent an approach which is a close simile to the fragile ecologies of cliffs in nature.  As a consequence they are vulnerable to disruption both natural and (for lack of a better word) administrative.  For instance, the greenery on 1 Central Park is looking decidedly ragged because of the natural forces of wind and sun, but it is even more threatened by the reluctance of the owners of many apartments to contribute to the expensive upkeep.  In my view, that kind of green wall will only ever make a small, perhaps negligible contribution to greening the city.

There is another way.  The pioneering example is Bosco Verticale ('vertical forest') in Milan.  When I first posted about that project, it was in the context of my cynicism about the fashion of photoshopping lush greenery on every skyscraper competition entry.  To support my doubts, I marshaled the reasoned criticism of  Tim De Chant who concludes that there are a couple of orders of magnitude difference between the effort required to achieve nominal tree presence on buildings as opposed to that spent on resuscitating the region’s natural habitat. But without repudiating my previous opinion, I have come to see the point of the vertical forest approach.

The difference between 'green walls' and the 'vertical forest' is technical, but simple.  Where the former relies on a thin veneer of plants supported by a thinner scaffold of growing media in mats or pots, the vertical forest approach sets out to create substantial volumes of soil in which to plant shrubs and trees.  The penalty is the extra weight to be carried by the structure, but the benefits are greater.  As with thermally massive construction, you have the inertia of both temperature and moisture regimes, that make the system much less vulnerable to exposure.  Even the issue of the extra weight is not so problematic, given it's dead weight acting vertically, the most easily resisted load on a structure. The sort of large structural planters used on the lower terraces of  WOHA's Singapore Park Royal are arguably a sub-set of this vertical forest approach. 

As with most pioneer schemes, the Bosco Verticale projects a single emphatic image, distributing its green terraces relatively uniformly over the building.  What prompted this post is a recent project announcement in Brisbane, Australia, where the balance between the conventional window wall surfaces and the part of the facade given over to the 'forest' is actually quite different.  In fact, so different, it would be easy to jump to a conclusion that the green parts are tokenism.

Closer examination of the scheme reveals  a subtly different reasoning.  The primary motivation is explicitly that apartments should 'feel' like houses in a garden, rather than more ambitious objectives of replacing larger ecological systems.  To that end, the architects respond with a simple apartment layout that maximises the apparent interface between the repeated two storey planted 'courtyards, and adjacent interiors.  Arguably, the precedent for this is Correa's Kanchanjunga Apartments in Mumbai, India, but with plants, rather than walls.

Developers may still begrudge paying for part of their building included more for the plants, than for the measurable occupied spaces.  And regulators may be slow to avoid penalizing the extra space within the built volume.  It may still be a pale imitation of nature in a real forest, or even in a good urban park.  But this latest example may be an effective demonstration for how to integrate elevated greenery that is both more robust and more economical than the green wall prototypes. If so, we can expect more people willing to pay a premium for their houses in the sky, with at least an illusion of arcadia outside their high rise windows.

See the Architecture & Design article here.

My previous posts:
Wrong green
No trees please.
Trees in the air 2

That heliostat again: enough already.

Now that Jean Nouvel's One Central Park apartment building has been invested with the exalted status of “Best Tall Building Worldwide” by the Council on Tall Buildings and Urban Habitat (CTBUH), it's time to put that infamous heliostat to bed.  Especially as it hardly got a mention in the metaphorical shadow of the breatless claims for the world's biggest, ot tallest green walls by Patric Blanc.

Up front:  The heliostat works as described in an earlier post in this blog.  See the diagrams and descriptions at "Clued in on the heliostat".  And a video here. No, it doesn't do anything to improve winter sun for the apartments at all.

No trees please.

For some reason, my posts about trees on buildings have had more attention than any other posts.  My core message has been that architects are putting trees into renderings of proposed buildings, in a disingenuous attempt to divert attention from the lack of any real progress towards truly sustainable new buildings - towards the more considered matrix of urban development that heals the environment in a true, complex way.

But I suspect most people, especially the architects, are ever more hopeful, and therefore my attempt to be balanced by commenting more or less positively on WOHA's Singaposre Park Royal as an actual built example, is possibly my most viewed blog.  Like other hopefulls, I also seized on the hoisting of the first tree into place on Milan's Bosco Verticale with some enthusiasm. Time for a reality check.

The original author of 'Can we please stop drawing trees on top of skyscrapers?' Tim De Chant is himself quite obviously a tree lover and advocate for reforrestation.  It is worth revisiting his rather more extended examination of trees on buildings, in that wider framework of marginal value of ecological rehabilitation.  In 'More reasons to stop putting trees on skyscrapers' back in April, he sets up a simple comparison between the Bosco Verticale and a 'real' forest, both in terms of monetary cost and ecological outcomes.  In his simple comparison, he uses figures from restoring woodlands in the US and from the intensely human modified countryside of Italy.  He even uses urban parkland, not unexpectedly Central Park in NY.

There is no mistaking his conclusions.  There are a couple of orders of magnitude difference between the effort required to achieve nominal tree presence on buildings as opposed to that spent on resuscitating the region’s natural habitat.  He dismisses the claim that trees on buildings are worth it for the inspiration: 

I see them as a distraction and potential liability—what if the Bosco Verticale becomes a brown eyesore, turning people off to his larger vision? I’d love it if Bosco Verticale and other proposed arboreal skyscrapers were sustainable and successful.³ Who wouldn’t want to live in a city full of tree towers? But I just can’t make a case for it. Plant physiology tells me that the trees, if they do survive, will require constant and costly maintenance throughout their short, brutal lives. Finance tells me that the money required to afforest a building would be more effectively used for restoration and preservation. And my gut tells me there are more equitable ways to give people trees, not just to those who can afford it.

I think he is right.  Which is not to say there is no ecologically and financially sound model for maintaining plant communities in cities.  De Chant emphasizes urban parks and street trees.  There are the 'green fingers' of managed drainage systems, doing triple or more duty as active recreation space and channels of cooling breezes in summer (Zurich in Switzerland is the most cited example).  At building level, there seems little problem in growing low scale vegetation on a modest amount of soil on horizontal roofs.  Not only can one realistically aspire to produce some edible crops, but the overall 'capacitive insulation' value of the roof can be demonstrated to have energy efficiency benefits.  The latter can be achieved even where we acknowledge that a lot of roofs have to be low water landscapes.  And even on high rise, large wintergardens can materially affect well being, partly trough measurable effects on air quality of conditioned interiors.

Just not gratuitous photoshopped trees, please.

Read More reasons to stop putting trees on skyscrapers on Per Square Mile.  The extended essay is supported by references.