Learn the pros and cons of wooden skyscrapers

The world's tallest wooden skyscraper has been planned in Tokyo, and could be as high as 70 storeys. While a hybrid of wood and steel, Sumitomo Forestry's building (dubbed W350) will be 90 per cent timber and is slated for construction in 2041. 

Similar structures exist here in New Zealand, although not nearly as tall. The iconic Oldins Building in Petone, Wellington, for example, was at the time of construction the second-largest timber construction in the southern hemisphere at a modest four stories  - second only to the old Wellington government buildings. We know Sir Bob Jones is planning to build the world’s tallest wooden office tower this decade in Wellington. Standing 52 metres tall, it is due to be completed in 2018. But all this talk begs an important question: Why build with timber high-rise construction at all?

Today, we examine both sides of the debate, and what Kiwi architects should know.

Pros of wooden high-rises

We've identified three important pros for timber skyscrapers:

1. Sustainability.
2. Workability
3. Growing prefab industry.

1. Sustainability

Timber is widely considered a better environmental option for construction. Significantly less carbon is produced during the manufacturing of wood compared to more energy-intensive materials, says Dr Scott Breneman, a senior technical director for US-based WoodWorks.

Wood also locks carbon, a process called carbon fixation - as a tree, it absorbs carbon, and so long as it doesn't rot or burn, that carbon remains locked even when the tree is chopped up. W350 is designed to have a carbon fixation equivalent of 8,000 wooden houses (or 100,000 tonnes of CO2).

2. Workability

The inherent workability of timber is one of its most touted features. Timber is fast and easy to build with, typically costing less than concrete or steel. In one example of large timber construction overseas, Kory Knudson, vice president of contracting company Norcon NW, told Building Design and Construction (BDC) Network that had his company used all concrete for one of its recent Seattle projects, the build would have cost 30 per cent more.

Additionally, Norcon NW's structure went up much faster than a similar sized concrete and steel hotel nearby.

"They had a lot of on-site welding, but by using wood, we were able to work through all types of weather," said President of Norcon NW Joe Hanley, also to BDC Network.

New cross-laminated timber fire tests back proponents of high-rise wood structures https://t.co/Q7YktGoFk5 pic.twitter.com/yFDt1T3oqr

— BD+C Magazine (@BDCNetwork) October 21, 2016

3. Prefab options available

Prefab construction is a growing industry here in New Zealand, particularly thanks to cross-laminated timber (CLT) manufacturers like Xlam. Though mostly in use in low-statured buildings, CLT high rises could be a cost-effective, and structurally sound, way to build upwards.

CLT is already in use around the world for this purpose - in Australia, the 52-metre 5 King building in Brisbane (due to be completed by the end of 2018) is made from both CLT and glue-laminated timber to gain the same strength as steel or concrete (with less of the environmental impact).