Serpentine Pavilion Is a Concrete Conundrum

It is a lovely idea. Every year since 2000, a temporary pavilion has been commissioned by the Serpentine Gallery, exposing Londoners to international architects who have not completed a building in the United Kingdom at the time of the commission. It sits in Hyde Park for just six months.

It is a wonderful opportunity to demonstrate ideas for lightweight, temporary buildings. The 2017 installation by Diébédo Francis Kéré is the only one I have seen, but it was all light, airy, and wooden.

The 2021 pavilion, designed by Johannesburg-based practice Counterspace with director Sumayya Vally, is a very different kind of structure: It looks like it is made out of concrete.

Critic Rob Wilson writes in the Architects Journal:

"The interior of the pavilion is more like an illustration of a space, more stage-set than building. With all the ledges and benches, and carved-out nooks and crannies, these are undoubtedly great spaces to stop, sit and chat in. But compared with the materially rich, visceral atmosphere of Junya Ishigami 2019 slate-roofed pavilion, the space here is rather bloodless. Its protean Pomo-detailed columns, formed by sheets of black cork, and micro-concrete faced plywood which wrap the steel frame, have an abstracted, almost 3D printed look to their forms."

I couldn't get over the resemblance to the park pavilion built in Toronto's Humber River Park. Architectural historian Chris Bateman described it in Spacing:

"Designed in 1958 by British-born architect Alan Crossley and consulting engineer Laurence Cazaly, the space age washroom and shelter in South Humber Park is a wonderful example of the exuberant architecture created across North America during the 1950s and 60s. Think the Space Needle and the Theme Building in Los Angeles on a smaller scale. Though Crossley and Cazaly were only designing a rest stop, their blueprints elevated a simple structure to something truly exceptional and joyful."

While the clunkier columns above grade are not solid concrete, what lies beneath has been causing some controversy, ever since one of the companies involved in construction sent out an unfortunate tweet in an era when so many British architects are sensitive about the issues of concrete and embodied carbon.

That's a lot of concrete for a temporary building, 125 cubic yards, roughly a dozen ready-mix truck's worth. Although the artistic director of the Serpentine promised to put the environment "at the heart of everything we do," according to Art Review:

"The vast quantity of concrete being poured into the ground (and carbon into the sky) to form the base of this year’s Serpentine Pavilion, somewhat calls into question the sincerity of that pledge (to put it mildly)," architect Thomas Bryans told the Journal.

Engineer Jon Leach of Aecom issued a statement defending it, noting the location, with "the very high footfall and multi-functional events that the pavilion hosts over its five-month installation" made concrete the most suitable material for foundations and the slab on grade.

“The concrete volume has been minimised structurally, maximises the use of cement replacements (GGBS, [Ground Granulated Blast furnace Slag] an industrial by-product), and will be recycled after the pavilion is moved to the next site as it has successfully been in previous years.”

But It's Carbon Negative!

More recently in AJ, engineer David Glover reiterated that it wasn't so bad.

Actually, it's 85m²,’ he says. ‘And given it's a 350m^{2 (}3767 SF) pavilion, that means the foundation is only about 250mm (10 inches) deep on average. This is necessary given it’s taking big point loads from a structure that in places is up to 8m (26') high.

This is the perfect engineer's answer; he was given a job to do, to hold up the building designed by the architect. It is always the engineer's answer, instead of saying that maybe he should have convinced the architect not to build a heavy 26-foot high building. He then goes on to say that "the pavilion overall is carbon negative by 9,000 tonnes – largely due to the reused steel of the frame." That is not possible with steel—he is crediting the structure with the emissions that would have been released had he used virgin steel, and that's not how it works.

The architect, Vally, is contrite, also calls it carbon negative, and says the artistic director Hans Ulrich "has said to me all future pavilions will now subscribe to being carbon negative." Since everyone is promising this, the accepted definition of carbon-negative is:

"The reduction of an entity’s carbon footprint to less than neutral, so that the entity has a net effect of removing carbon dioxide from the atmosphere rather than adding it."

In other words, make it out of wood, cork, straw, bamboo, or other natural materials that remove carbon dioxide when they grow. Period. No credits for avoided emissions. And while we are at it, just ban the use of concrete, which in these times makes no sense in a temporary structure.

Wilson wonders if they should be building the Serpentine Pavilion at all, and he has a point. Perhaps they should pin this on the studio wall and bring the World Green Building Council into the discussion, who start with building nothing and end up with building efficiently, using low carbon tech, and eliminating waste. It would be a very different Serpentine Pavilion.