70 Story tallest timber tower tipped for Tokyo

W350 aerial view
© Sumitomo Forestry

Sumitomo Forestry has a lot of wood to use up.

Sumitomo Forestry, an industry giant in Japan, has a problem. Most of their wood goes into building houses and, with a shrinking population and a dislike of immigration, there are not a lot of houses being built. So they are pivoting to plyscrapers, and proposing a 70-story, 350 meter (1148') tower for the Marunouchi district in Tokyo. It's called W350, the plan being that it will be finished in 2041, the 350th anniversary of the founding of the company. I have previously wondered whether these tall towers are too much of a wood thing, but they are taking their time here and have an interesting rationale for it.

W350 Lobby© Sumitomo Forestry
According to Johnny at Spoon and Tomago,

Using a hybrid 9:1 ratio of wood to steel, Sumitomo Forestry aims to replace concrete, which is one of the world’s largest carbon footprint contributors. The skyscraper would be a 70-floor mixed-use building that would include a hotel, office space, commercial space and residences. Wrap-around balconies at different intervals would be planted with lush wildlife. And greenery would extend throughout the entire complex, creating a vertical forest where humans and wildlife can flourish.

balconies© Sumitomo Forestry/ balconies with fire-resistant plants

A Japan Real Estate site tells us that "the outside of the building will be encircled by balconies and fire-resistant plants." The building will have 455,000 M2 of space (4.9 million SF) and be built from 185,000 cubic meters of wood, which is enough to built 8,000 single family homes. It will fix 100,000 tonnes of carbon dioxide in the wood. Sumitomo claims that 2/3 of Japan is forested and that many trees replanted after the war need to be cut, or they will die and rot.

Interestingly, Sumitomo is designing the building so that elements can be maintained for a certain period of time and then replaced as needed.

The used wood can be recycled and used as residential pillars and beams, and then used as a raw material for new wooden building materials, so that it can be circulated in the city. The final waste material can be used as fuel for biomass power generation and cascade usage of wood can be used such as using heat generated at the time of combustion of biomass power generation for drying wood.

brace tube structure© Sumitomo Forestry

It is a brace tube structure, "a structural system that forms a cylindrical shell (brace tube) with columns / beams and braces. By placing braces diagonally in a set of shafts assembled with columns and beams, it prevents the building from deforming against lateral forces such as earthquakes and wind."

And in answer to the concern that may be at the top of most people’s minds, Sumitomo Forestry says it will research wood-based materials that can withstand flames for three hours.

There is a cute video on the Sumitomo website.

Tower section© Sumitomo Forestry

70 Story tallest timber tower tipped for Tokyo
Sumitomo Forestry has a lot of wood to use up.

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