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Architects and developers are “running away screaming at the idea of using CLT”

After a tragic fire caused by plastics, the British building code banned wood in exterior walls. This is a step in the wrong direction.

After the horrific Grenfell fire, where plastic windows, plastic foam insulation and a plastic cladding all caught fire, the first lesson that should have been learned is that we should not clad buildings in flammable plastic. I said at the time that this should not become an indictment of wood construction:

People are already circling on this. Heavy timber and cross laminated timber do not burn like plastics; they char and take hours, not minutes, to catch. The buildings made of it are usually sprinklered. It is not the same thing, but I guarantee that the concrete and masonry people are already composing their advertisements.

And indeed, the building regulations were changed to ban the use of combustible materials in exterior walls. They didn't even just ban combustible cladding, but anything in the wall. This makes no sense; fire simply cannot spread up a wall with wood inside noncombustible cladding as it did with exposed plastic that acted like a chimney. Architect Andrew Waugh said at the time that the code change “demonstrates a misunderstanding of the fire performance of engineered timber”.

Alex de Rijke of dRMM was quoted in Dezeen saying “this political knee-jerk reaction is uninformed and counter-productive. Banning safe timber construction prevents the creation of healthy and safe cities, and worsens the global environmental crisis of carbon emissions due to use of materials like concrete and steel.”

And now, Alex de Rijke is out of a job designing a CLT building in London, replaced by Studio Partington, who have switched the whole building to concrete. The new firm is quoted by Ella Jessel in the Architects Journal, saying that keeping the wood structure made it too complicated.

If the CLT frame was to be retained in the design of the building this would have meant introducing three structural systems (one for retail areas, substructure and cores; one for internal apartment walls and floors; and one for the external walls) leading to unnecessary complexity. The change to a reinforced-concrete frame provided a number of structural and cost efficiencies allowing for improvements elsewhere, for instance an increase in the number of affordable homes.

Alex de Rijke says it would not have been a big deal.

“dRMM’s original scheme was conceived in CLT not only for the enormous environmental benefit in terms of embodied carbon, but also for structural efficiency…‘It is perfectly possible to build engineered timber buildings and comply with the new legislation by placing the timber structure inboard of the façade zone. Complexity is not necessary or inevitable. In reality, the practical construction advantages of prefabricated timber buildings over in-situ concrete are legion, including faster build speed, fewer deliveries, smaller workforce, fewer trades, a safer process and healthier working conditions.”

The two firms are fighting it out in comments, with Richard Partington calling this discussion “misinformed” and claiming that the new building has even less concrete in it than the original.

It's always a mess when an architect gets fired, and even worse when it gets down to counting buckets of concrete. But it's also problematic when, as Simon Aldous notes that because of the rule changes, “many housing developers are running away screaming at the idea of using CLT anywhere on high-rise projects.” The material had such promise in reducing the upfront carbon emissions of construction by reducing the amount of concrete and steel needed. The breakthroughs in using this material happened in the UK, and now it seems they are putting on the brakes. This is unfortunate.

After a tragic fire caused by plastics, the British building code banned wood in exterior walls. This is a step in the wrong direction.