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Environment / Climate change

World's tallest wooden skyscraper planned for Vienna; city's fire service concerned

Unlikely as it sounds, wooden skyscrapers are a thing these days. As we noted last year, concerns about the environmental impact of steel and concrete are driving some architects and designers back to wood as a more eco-friendly alternative. There’s already a nine storey tower built from specially laminated timber in London, and a 12 storey wooden building under construction in Bergen, Norway. 

A planned tower for Vienna, however, is due to leapfrog both in terms of scale and height. The HoHo project in Vienna’s Seestadt Aspern area will feature two wooden towers, the tallest of which will stretch to 25 storeys and 84m. The towers will be 76 per cent wood; Kerbler, the firm behind the designs, claim the material will produce 2,800 tonnes of CO2 when compared to a similar sized tower built from concrete.

However, according to the Guardianthe plans didn’t go down so well with the Viennese fire department. Christian Wegner, spokesperson for the department, said:

A few of us were upset because it was crazy to present an idea like this that has not been discussed with everyone yet.

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They have to carry out special tests on the correct combination of concrete and wood. We also want to develop a more fail-safe sprinkler system. I expect they will pass the tests but if they develop the building as they say they will, it will be a serious project.

The fire service is now working with the architects to ensure the building meets safety standards. If all goes to plan, construction will begin later this year, and should be completed in 2016.

Despite the fire service’s hesitancy, the tower’s height shows that planners and designers alike have a growing faith in the safety of timber structures. In the UK, it was against planning regulations to build a timber structure above three storeys until the early 2000s, when safety tests showed that taller timber structures could meet the same safety regulations as concrete or steel ones. Recent tests in Canada, meanwhile, have shown that timber treated in the right way can resist heat and flames for up to three hours.

Daniel Safarik, editor of the Council on Tall Buildings and Urban Habitat, says resistence to wood-based construction stems from a lack of understanding around the materials on offer: 

[The Vienna project] will encounter some of the same issues as other structures in obtaining approvals, mainly that the local fire codes are often predisposed against wood as a material, due to the combustibility of traditional stick framing.

Cross-laminated timber panels, however, are quite thick and develop a “char layer” that allows them to support the building for several hours during a fire – just as concrete or masonry would. Most of the buildings we have seen proposed are not “pure” wood structures anyway. Many use some combination of steel, wood and concrete. In general, the arguments in favour of wood construction are strong. 

In summary: building giant towers out of wood is actually much safer than it sounds. 
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