ou don’t have to be an expert in construction to know that wood burns. You might also recall that parts of London were destroyed in the Great Fire because they were made largely of wood, after which they were rebuilt in brick and stone. So it will seem a reasonable reaction to the Grenfell disaster that the government banned timber (along with other combustible materials) from the exterior of residential buildings more than 18 metres high.
This ban started in 2018, with the promise to review it. Now it is proposing both to continue and extend it so that it covers buildings more than 11 metres high, and uses such as hotels as well as blocks of flats (in England only – Scotland and Wales have slightly different arrangements). Better, you will probably think, to be safe than sorry. But there’s a cost to this caution, which is that it will impede one of the most promising recent innovations in building.
This is the engineering of timber so that it can act as an alternative to steel and concrete, such that large and tall structures can be built with it. Its environmental benefits are compelling: whereas concrete is a particularly devastating material, said to account for 4%-8% of the world’s CO2, timber locks up the carbon absorbed by the growth of trees. While construction is a major contributor to greenhouse gases, building in wood has the potential to reduce them.
There are other advantages. Current techniques mean that timber structures can be made into components away from building sites and then assembled there, which has benefits for quality, precision and speed of construction. It is lighter and easier to transport than its alternatives. It is versatile and can be used to make walls and floors as well as the frames that hold buildings up. Wood is an inherently pleasing material, both visually and acoustically.
It makes for building sites that are cleaner, safer, quieter and more pleasant – think of the difference, in terms of the effects on your ears and arms, between drilling into wood and into concrete. Engineered timber requires fewer workers on a building site and, given that construction workers now account for a large number of Covid-19 cases, the benefit is not purely economic. As for the question of fire: if it is thick enough and dense enough, wood burns slowly, because it protects itself from further damage by charring, whereas at high temperatures steel is given to sudden collapse.
Not surprisingly, given its many qualities, the use of engineered timber is expanding around the world. In Vancouver, where an 18-storey timber tower was completed in 2017, one of 40 storeys is now planned. It was reported last year that nearly 500 mid-rise timber buildings were under way across Canada. A 70-storey timber tower has been proposed in Tokyo. Norway, as might be expected, is an enthusiastic early adopter. In France, President Macron has decreed that all buildings funded by the state must be at least 50% wood. All buildings for the Paris 2024 Olympics must be all-timber if they are under eight storeys high.
Britain’s main contribution has been through its architects and engineers. The architectural practice dRMM has been finding creative uses for engineered timber for two decades; another, Waugh Thistleton, has used it for multistorey housing in London and an industrial building in Warwickshire. The 2018 ban, however, has cut short these architects’ contributions. A timber-built 11-storey housing tower by dRMM, in the London borough of Newham, has been cancelled.
High-performing timber construction will continue to expand, in other words, in many parts of the world, but will be held back in England. Of course no one should be blase about what is a fast-developing technology and continuing testing and research are needed to ensure its safety, but the same is true of many techniques used in modern construction. For all these reasons, a number of organisations and businesses, including the Architects’ Climate Action Network and the Royal Institute of British Architects, have urged the government to reconsider.
Part of the problem is that the current ban doesn’t adequately distinguish between the cladding, or outer skin of a building, and its structure. There is almost universal agreement that it is reasonable to ban timber cladding on buildings of more than a few storeys high. But one of the beauties of engineered timber is that it can function as the stuff that does the hard work of holding a building up, as the layer that encloses the interior and as the surface that you look at. While it is possible to conceal a wooden structure beneath another material, this loses much of the simplicity that is one of its advantages.
A strange aspect in all of this is that Grenfell Tower was not made of timber, but of reinforced concrete clad in polyethylene and aluminium. While the Grenfell inquiry, which has been delayed by the pandemic, has not reached its conclusions, it is perverse to ban a blameless material while we’re waiting.
It is easy to imagine the headlines that a politician would fear if a wooden building were to catch fire in the future. It will take a smidgen of courage for the communities secretary, Robert Jenrick, whose department is responsible for building regulations, to make an exception for structural timber. What matters most is its potential for economic and environmental good. He should not be in the business of the pointless prohibition of such a thing.
oRowan Moore is the Observer’s architecture critic