Monday, 24 June 2013

Another world's tallest?

A number of sites have recently featured a proposal by Scandinavian firm C. F. Møller to construct the world's tallest timber-framed building in Stockholm, Sweden. The project is shortlisted in a housing design competition, organised by Swedish building society HSB Stockholm.  The winning entry in the competition is scheduled to open in 2023 to coincide with the organisation's 100th birthday.

The 34-storey Wooden Skyscraper is put forward as a vision of future housing that would be cheaper, easier and more sustainable than typical steel and concrete constructions.  To support this proposition, the architects spell out the usual message of replaceable managed plantings, some loosely framed claims for the thermal performance of timber as structure and internal finishes, and in particular the counter-intuitive fact that engineered timber construction can outperform steel and concrete in fire safety.

I agree with all the headline claims, but as usual regret the imprecise detail.  And that looseness leads to a predictably wide ranging response of impassioned comments on sites like Dezeen.  The key concepts that put high rise timber construction in context are:
  • Using timber is an excellent way of net carbon capture, as opposed to any other form of construction, which all emit large quantities of greenhouse gases in manufacture and transport;
  • Timber can be supplied from sustainably harvested plantings.  There is no point confusing the deforestation for agriculture, or the unregulated exploitation of high value rainforest, with the existing and future managed forests.  Both Scandinavia and Japan, already famous for timber, have forests that are growing faster than they are being harvested.  In Japan, this is just one outcome of the loss of other economic justifications for traditional forest management (known as satoyama).  The problem is so severe, that there are institutions such as the Gifu Academy of Forest Science and Culture dedicated to increasing the 'exploitation' of former traditionally managed forest, before it looses its economic value.
  • Timber construction doesn't only make sense when the resource is 'local'.  There is a seductive concept known as the 'woodmiles index' that compares the overall sustainability of supplying timber by factoring in its transportation.  Of course, one of the uncomfortable facts it demonstrates is that the embodied energy due to the transport component is usually smaller when the timber is transported half way around the world by ship, rather than across the state by truck.  So the key is how far from a port the source and destination happen to be, and how effectively organised is the manufacture of the timber components.
  • Timber is not a material with thermal mass in the same sense as concrete or masonry.  Because thermal storage is an indispensable part of passive solar and passive cooling strategies, the first assumption would be that timber construction instead fits into the 'energy conservation' category.  Which is why it is found mostly in cold climates rich in timber for both fuel and light weight, insulated construction.  But even that boundary is being blurred by the increasing availability of commercialized phase change materials, which may be incorporated in light construction.
I could go on, but a blog is not a great place for an exhaustive technical text.  I want to comment on some other aspects of the proposal. 

The most conspicuous is that it is actually a high rise with a skin almost entirely of glass.  Technically, of course, that can be described as a wintergarden approach to the layered occupied space, with flexible boundaries which can respond to the climatic extremes.  The architects can't resist describing it instead as an aesthetic decision to make visible the interior timber construction, so they forgo optimizing the proportion of glass in the inner wall.  No wonder we architects are so often accused of being wankers.

Typical floor plan.  Click for larger image.
There are other points of interest.  The typical plan shows modernist rationalism in the circulation space taken to an unusual extreme, even for European apartments.  I don't often see a lift lobby serving four apartments quite so tight.  And the arrangement of the fire escape stairs is either ingenious, or absurd.....accessed from the wintergardens, they appear to be clad with glass on all sides.  In the case of at least one apartment per floor, the source of daylight to a bedroom is entirely through the stair enclosure.

The coding of the plan suggests a curious reluctance to use the partition walls as load bearing structure or as shear walls for lateral bracing, quite unlike the ten storey Forte apartments by Bovis  Lend Lease completed in Melbourne, Australlia last year, and which are a showpiece for cross-laminated timber (CLT), which is manufactured using layers of timber to create solid panels. But the architects don't seem to know that the Forte is actually the tallest finished timber apartment building in the world, so that is not surprising.  Other than a cryptic reference to the possible substitution of timber for the presently proposed concrete core of the tower, there is no information from which to infer its structural rationale.

I won't make much of glib claims that rooftop photovoltaics will power the building, when in reality they will contribute a miniscule proportion of the total energy budget.  That sort of thing is normal for competition rhetoric.

But of course, it's early days.  Design development will answer many questions and possibly abandon less fruitful design ideas., The most important consideration at this time is that a team of architects and engineers are putting in the research to establish proof of concept for a potentially important transformation of our choices in building materials.

Incidentally, anyone can vote for the winner of the competition using the HSB Stockholm Facebook page. as long as you speak Swedish.  Which seems fair.  What isn't fair, is that it appears you get to vote on the usual pretty renderings, rather than the copious and rigorous materials the internet could deliver.

Google will give you another hundred articles based on the same press release, and many of them on the Dezeen version of it..
See it on Dezeen here

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