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

Trees in the air 3: you can see the forest!

I reported a year ago on early news of the Bosco Verticale project in Milan, by Italian architect Stefano Boeri.  At the time, it was tempting to be dismissive of what appeared to be just another architectural rendering with gratuitous vegetation, and my blog post put more emphasis on Tim De Chant's cririque, unfavourably comparing the idea to the preservation of 'real' forest.

It’s hard to be cynical now that the project is nearing completion, and the vertical forest already has a compelling presence in its neighbourhood.  As seen in Dezeen's extensive coverage, the aerial forest looks lush and healthy.

The irresistible comparison is between the approach taken by the Italian building, and the Jean Nouvelle building Central Park One in Sydney, sporting what has been dubbed the world’s biggest vertical garden, by the French botanist Patrick Blanc.

Are trees good for you?

Of course they are.  I firmly believe that.  Obviously, so do advocates of urban forests. Oh, yes, I am one of those.

Advocacy for increased attention to tree scale planting in cities, for the establishment of viable urban forests, is at least a generation old.  And even though rarely adopted as a coherent policy by cities during that time, there has nevertheless been a distinct trend for the public and private domains to acquire significantly more green fuzz.

Paddington, Sydney 2012

It is quite enlightening to compare old aerial photographs of 'inner ring' suburbs of a city like Sydney, with recent images.  It becomes clear how little greenery featured in these places when they were a dense matrix of unregulated industry and predominantly worker housing, strung together by tramways and above ground electricity and telephone wiring.  In contrast, gentrification also seems to bring a commitment to transforming bare streets to treed, and small gardens to intensely planted havens.  In particular, not so many people these days seem to share the former suburban phobias about gutters blocked by leaf litter, so they don't maintain personal vendettas against trees taller than three meters.

Paddington, Sydney, 1947

But lately there also seems to be a more concerted push towards urban forests, driven by a loose conception that greening the city will help do away with the so-called 'urban heat island effect'.

The latest such initiative I have come across is from Melbourne, Australia, already one of the worlds most livable cities.  The article is on Sourceable.net, and may very well have some of the usual baggage of journalistic oversimplification, but I suspect that the point I am about to tease apart is not one of them.

Thermal image of inner Melbourne

As almost always, the key image in the argument for the putative benefits of a green canopy is an aerial view as a 'false colour' thermal photograph.  The image supporting the Melbourne press releases is the prettily coloured one I reproduce in this post.  What you are meant to see is that all the parklands show up as reassuringly blue-green cool, in contrast to the warm yellow-reds of all the concrete and asphalt of buildings and roads.
 
But now look more carefully.  Look for all the coolest surfaces, the ones in the most intense blues.  I am not really familiar with Melbourne, but I can tell by the shapes that the coolest surfaces are in fact the metal roofs of the sporting venues, and indeed of the large industrial and warehouse sheds.  Now, I don't know too much more about the total heat balance over time, of these lightweight roofs as opposed to the grass and canopies of the areas of vegetation.  But I am sure my reading of the pretty picture is not going to be popular with the people who would like it to be self-evident, that literally greening the city will by itself make the urban heat islands go away.

Most readers of my blog would be familiar with my obsession with looking more carefully at data and imagery, particularly when looking for evidence of technical performance.  Well, this is one more example.  In fact, US research suggests that simply extending green surfaces by way of street planting and vegetated roofs makes far less impact on the city's average albedo than we would hope.

Which is not to say that a lot of the other benefits of trees in cities are not worth it for their own sakes.  I'd rather a shaded street sidewalk to walk along than to bake in the merciless sun of a Melbourne summer, I'd rather the leaves overhead cooling and humidifying by transpiration the microclimate under them.  But to capture that correct depiction of what happens, you need to show thermal images of the street at pedestrian level.  It would be just as compelling as the misinformation of the thoughtlessly chosen and misleading aerial.

Read the Sourceable.net article here.

To see another similar aerial thermal image, with exactly the same issues, see the ones of Sydney, here.  But if the reader is interested, this page also links to other microclimate monitoring by the City of Sydney.  If really, truly interested, take the trouble to go to the UNSW link and download the full report of the pilot project
Micro-Urban-ClimaticThermal Emissions: in a Medium-Density Residential Precinct.  Don't be put off by the poorly written report itself, and spend your time instead on the comprehensive literature and methodology review in Appendix 1.

Micro-Urban-Climatic Thermal Emissions: in a Medium-Density Residential Precinct - See more at: http://www.be.unsw.edu.au/sustainability-and-climate-change-adaptation/projects/thermal-impact-designed-environment-urban-heat#sthash.Y6relWBT.dpuf

Thermal Impact of the Designed Environment on the Urban Heat Island - See more at: http://www.be.unsw.edu.au/sustainability-and-climate-change-adaptation/projects/thermal-impact-designed-environment-urban-heat#sthash.Y6relWBT.dpuf

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.

Trees in the air 2

The opening of WOHA Architects' new Park Royal complex in Singapore appears at first sight to make nonsense of my recent post about trees on buildings (see Wrong green).  Or at least the hero shot makes it seem that way.

I felt a lot less threatened when I saw other images of the same building.  As usual, the camera so easily frames a potentially misleading message.

But I don't want to be churlish.  A lot of credit must be given WOHA for some remarkable aspects of the scheme.  The skygardens with their extended planter beds create micro environments and micro-climates that appear to radically transform the experience of circulation on upper floors, further enhanced by the use of natural materials such as light and dark wood, pebbles and water. There are technological systems with automatic light, rain and motion sensors, rainwater harvesting and recycling.  Enough sustainability bling to ensure the Park Royal on Pickering has been awarded the BCA Green Mark Platinum-the highest rating for green buildings in Singapore, And even the jarringly slick glazed tower bits can be favourably read, if one recognises that the choice of a narrow floor plate has made it possible for the interiors to be flooded with natural light.

This one I definitely want to see in real life.

Read more: Park Royal Tower: WOHA's Stunning Vertical Garden Tower Opens in Singapore

Wrong green

This is an update/re-write of a post that lost its links.

Wish I had got my brain in gear long ago, and done it myself.  In a short but effective article by Tim De Chant at Slate, titled
Can We Please Stop Drawing Trees on Top of Skyscrapers? finally someone has taken the trouble to state the obvious:

Architectural design proposals often depict high-rise buildings with trees flourishing on rooftops in an attempt to look more ‘green'.  Despite this, trees and skyscrapers are a lethal mix – for the trees.  Regrettably, trees rarely survive on the top of skyscrapers, undercutting ideas of including them as a nod to sustainability and environmental friendliness in the renderings.

The article sets out the fundamentals: extremes of temperature, destructive wind velocities, and the immediate threats they pose to the normal biological functions of trees – from structural stability, to delicate osmotic gas and vapour exchanges in the normally protected boundary layer of air.  Anticipating the logistical difficulties of maintenance is not exactly rocket science, either.

The case against trees at great heights is easy to make, and is contrasted with the relatively easy path to conventional roof gardens on lower rise, high density apartment buildings..