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The world’s tallest wodden building has been exemplarily fireproofed

Just outside Oslo, in the town of Brumunddal at the Mjøsa lake, stands the Mjøstårnet tower. It is the world’s tallest timber building with its 18 floors distributed on 85.4 metres. The tower has wooden bearing structures, and the façade consists of prefabricated wooden façade elements.

Brumunddal | Norway
Realised, 2019
AAB Invest A/S
Hent A/S | Moelaven Limtre AS
Voll Arkitekter
15.000 m2
Detailed design, constructions, acoustics and fire protection

The high-rise tower has multiple functions: The ground floor is public and includes a lobby, reception and restaurant as well as public swimming baths. The next floors have meeting and conference facilities, offices, hotel rooms and 27 private apartments. The top floor of the building consists of a penthouse and a publicly accessible belvedere platform.

Mjøstårnet træsamling
Mjøstårnet trædetalje

A fire technical challenge

The multifunctional use means that there is a wide range of users in the building, which is, in itself, a fire technical challenge involving more continuous control of the building.

“The great challenge of constructing such a tall timber building is first and foremost to create a structure that is sufficiently strong and that does not sway too much in the wind. Here the choice was a combination of a lattice structure and the use of concrete in the upper floor decks. This gives the tower stability and contributes to better sound insulation between the dwellings,” explains Hjalte Bengtsson.

During his three years with Sweco Norway, Hjalte was involved in the fire protection of Mjøstårnet:

“Mjøstårnet has been exemplarily fireproofed. The building is designed so that, in the event of fire, the laminated wood structures used will form a thick coal layer that acts as a fire retardant. Once the furnishings have burnt out, the fire in the structures will die out by itself. The structures will be completely blackened, but the charcoal can be peeled off, revealing fresh wood beneath the surface. In this way, the wood fire protects itself,” explains Hjalte Bengtsson, adding that he would feel more secure living in Mjøstårnet than in a similar standard high rise of concrete in Denmark.

Mjøstårnet won the Norwegian Tech Awards, Building & Construction, in 2018 and received gold in the New York Design Award 2018 in the category ‘Architecture – Mixed Use – International’.

Mjøstårnet was built under a turnkey contract by the turnkey contractor Hent AS for the developer AB Invest AS. The project was handed over and commissioned in March 2019.

Mjøstårnet facadedetaljer