Tall timber: how high can CLT go?

There is considerable excitement about building tall with engineered timber, but it has been slow to translate into real-world structures. Towers of 30 or more storeys in Paris and Stockholm failed to materialize, and arguably the tallest in the world today is Treet, or The Tree, a 49m 14-storey apartment block in Bergen, Norway, completed in 2015.

This superseded Melbourne’s 32m Forté building, constructed by Lendlease from a “flat pack” of CLT panels acting as shear walls. In contrast, Treet has a glulam load-bearing structure supporting 62 prefabricated modular flats with walls made from CLT. Building stiffness is achieved solely through the glulam structure, though further stability is provided by concrete slabs which form the floors at levels six and 11.

Taller still is 53m Tallwood House, a student residence in Vancouver. Just completed, the 15,000m² project has a hybrid structure, with 17 storeys of CLT floors supported on glulam columns on top of a concrete base, and two 18-storey concrete cores. The building envelope is a prefabricated panel system clad with wood-fibre high-pressure laminate. Its designers claim that the structure is some 7,500 tonnes lighter than a concrete equivalent.

It was also surprisingly quick to construct, completed in nine weeks with only ten workers, according to Ralph Austin, president of contractor Seagate Structures. “Mass timber isn’t suited for every project and it isn’t going to solve our cities’ housing crisis alone, but it should be considered as another valid and valuable solution,” he says.

This article appeared in The Possible issue 02, as part of a longer feature on advances in construction materials