What does a northern Swedish city have to teach us about eco-friendly, wooden skyscrapers?

Posted by Derek Mason

23rd November 2021

Keeping up to date with climate crisis news can get a little depressing at times, so let’s take a moment to celebrate the planet-friendly timber structures that are going up across the world.

When I first wrote about timber skyscrapers, back in 2017, it seemed surprising that such tall wooden structures were going up. But as is often the way with tall buildings, there’s an element of “competitive sport” to this now, with increasing numbers of “plyscrapers” going up across the globe.

One particularly inspiring structure is the Sara Kulturhus a 20-storey Wood Hotel in Skellefteå, Sweden. At 75 metres, it is not quite the tallest in the world, but it is carbon negative, with locally sourced materials for both the building and its contents. The cultural centre houses a museum, art gallery, two theatres and a library, with the hotel tower alongside.

The city of Skellefteå, to the north of the country, has made the most of the 480,000 hectares of forest surrounding it. Aside from the structure I’m focusing on here, there are wooden schools, bridges and car parks, and even a wooden air traffic control tower.

All of the trees for this build were taken from within a 60km radius of the site, and the forests have since been replanted, even though the hotel has only just opened its doors.

As I’m sure you know, it’s not possible to build a safe, structurally sound skyscraper from raw lumber, so the main materials in this eco-friendly build are cross-laminated timber (CLT) and glued laminated timber (glulam).

Glulam is made from layers of timber bonded together, with the grain running the same way. This gives it a high load-bearing capacity – weight for weight its capacity is greater than that of steel and concrete. The columns and beams are made from this, whereas the walls, floor slabs and lift cores are made from CLT. In the tower, prefab hotel room pods are stacked on top of each other, with glulam columns in the corners for strength.

Because the timber can be left exposed, this means that plastering and decorating isn’t required. Timber construction is much quicker than traditional builds. It took only two days to build one storey, as the pieces came from factories and simply needed to be bolted together.

Truck deliveries were 90% less than on a standard site too, and there was almost zero waste, meaning that this was a genuinely eco-friendly build – not a “greenwashed” project.

As you might expect, it took three teams of structural engineers to make this build work, and there is, of course, some steel and concrete. Large steel plates are bolted through the walls on the fifth floor, with a steel truss that transfers the weight of the tower to the walls of the cultural centre. This allows a space free of columns in the theatre below. There is also concrete in the top two floors, to stop the tower from swaying in the wind.

It’s good to imagine a world where many more projects embrace sustainability in this way. At the time of writing, I believe the tallest, completed timber building is the 85.4m high, 18-storey Mjøstårnet in Norway.

But in Japan, a timber company has proposed a 70-storey skyscraper to mark their 350th anniversary in 2041. Named W350, not only would it be the world’s tallest wooden building, but it would also be Japan’s tallest building at 350m.

It will be interesting to see whether London joins in with this “competition”. When it was completed in 2017, Dalston Works was the world’s largest CLT building, but at 10-storeys it was never in contention for the title of “tallest”. There’s also a 300m timber tower proposed for the Barbican complex – nicknamed The Toothpick – but it’s still in the research phase.

It’s good to see our cities embracing timber construction, and let’s hope we see continued growth. Meanwhile, if you need assistance with the structural elements of an upcoming project, please do get in touch.

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