Using wood as the main construction material, even in high-rises, is key to shortening the construction time and, consequentially, cost. Modern technology enables us to prefabricate all components in a factory with a very high degree of precision. Compared to cast-in-situ concrete, wood makes it possible for construction time to be slashed by half. In addition, it's relatively easy to make adjustments or corrections on-site.
"The floor structures, which consist of massive beams with Kerto panels on top, are assembled in our factory, just 15 kilometres from the construction site. Obviously, that's a huge advantage if you have something that needs to be adjusted at the factory. The work is progressing at the rate of one storey a week, which has shortened our construction time by approximately 35 to 40 per cent compared to using cast-in-site concrete. And since the wooden components are so lightweight, we don't need the machinery to be as heavy," says Rune Abrahamsen, Managing Director of Moelven Limtre AS, a general subcontractor in the Mjøsa Tower project.
Using wood means greater fire safety
Fire safety is not a weak point in the wooden Mjøsa Tower. Untreated solid wood creates its own fire-resistant surface because the outermost layer chars when exposed to fire, protecting against further fire damage.
In fact, wood is a fireproof material despite the commonly held belief that it isn't. "Fire safety rules state that buildings must be able to withstand a full fire for at least two hours without collapsing. When you have a building made of steel and concrete, the steel melts and the building collapses," says Erik Tveit, Project Manager at HENT AS, the general contractor for the site.
Nevertheless, concrete will be used between the floors of the Tower's top seven storeys. Using concrete has nothing to do with the load-bearing capacity. There's a simpler explanation: the swaying that increases the higher you get in a building built of wood or concrete. The weight of the concrete in the upper storeys makes the swaying slower and not as readily perceivable.
Metsä Wood is supplying Kerto LVL to Moelven Limtre AS, which is constructing the wooden frame for the general contractor HENT.