Design for Living: The rise of timber

Switzerland's Rocket&Tigerli complex will include the tallest wooden building in the world. Illustration / Artist's impression

Heard about the concrete catastrophe? Early last century, cement made up only 15 per cent of all global construction materials. By the 1970s, it was 60 per cent and still climbing. Almost all large buildings and many smaller ones are made of concrete, along with most public structures, all tunnels, airport runways, footpaths, bridges and many roads. It’s the second-most consumed substance on the planet – the only thing we use more of is water.

And every kilogram of cement produces half a kilogram of CO2. Concrete accounts for 8 per cent of the world’s greenhouse gas emissions.

This has now created another problem. While concrete is almost impossible to crush, it doesn’t easily hold together. For that, you need reinforcing steel (what Americans call rebar, or reinforcing bars). But concrete is permeable, which means CO2 gets in. This causes the rebar to rust, and when it rusts it expands, and when it expands it cracks the concrete.

This wasn’t a big problem for the first few decades of the post-war construction boom, but there is vastly more CO2 in the atmosphere now, in part because of concrete.

Reinforced concrete has an estimated lifespan of perhaps 100 years and already some structures are failing or showing clear signs they will soon fail. Concrete has begun to eat itself.

What can we do? One answer is to build with wood. In Auckland, the city mission’s new headquarters, HomeGround, designed by Stevens Lawson Architects, is made from cross-laminated timber (CLT). Think of it as enormously thick sheets of plantation pine, glued together like plywood. It’s fire-resistant, versatile and strong enough for high-rise construction. At 11 storeys, HomeGround is the tallest wooden building in the country.

HomeGround in Auckland is the tallest wooden building in New Zealand. Photo / Mark Smith

Wood requires far less energy to produce and build with: HomeGround’s whole-of-life emissions will be 80 per cent lower than a conventional building of the same size.

The tallest wooden building in the world is Mjostarnet, an 18-storey mixed-use block in Norway designed by Voll Arkitekter. But it will soon be supplanted by the 32-storey main tower of a complex called Rocket&Tigerli in Zurich, Switzerland, designed by the Danish firm Schmidt Hammer Lassen Architects.

Currently the tallest wooden building in the world: Mjostarnet in Norway.

Rocket&Tigerli means Rocket and Tiger and recognises the names of locomotives that were once built on the site. The complex will contain “high-quality housing”, a student hostel, restaurants, a sky bar and a hotel.

Rocket&Tigerli, like HomeGround, will be held up by an internal laminate core and will feature terracotta cladding.

Is this the beginning of a new age? Cities need to build up, not out, and they also need to reduce emissions. Will CLT become the key to progress in construction?

Not so fast. For wood to concrete, we would need to cut down all the rainforests and plant pines everywhere. It’s not remotely possible or desirable.

Building with wood will be part of the solution, but only part. We’ll also need other changes, including better concrete. That’s on offer too: stand by for more.

The ground-floor restaurant in Mjostarnet.

Artist's impression of an apartment in Rocket&Tigerli, Zurich.

Design for Living, devoted to bright ideas that make cities better, appears weekly in Canvas magazine.