When it opened in March 2019, the Mjösa Tower became the world’s tallest wooden building. Fast to build with, light and green Kerto® LVL (laminated veneer lumber) from Metsä Wood plays an important part in strengthening the floors.

Mjösa Tower is a dream come true for Norwegian private investor Arthur Buchardt. He wanted to build the world’s tallest wooden building in Brumunddal in Norway on the shores of the country’s largest lake, Mjösa. The tower provides homes, office space and a hotel for people wanting something different. And what an 18-floor building it is; it not only stretches up to 85.4 metres in height but is built in a truly unique manner.

The Mjösa Tower symbolizes environmental trends in construction, and it is proof that tall buildings can be built using local resources, local suppliers and sustainable wood products. In addition to Norwegian glulam and CLT, the building makes use of Kerto LVL products delivered from Finland.

Traditional design on a large scale

The design approach used for the Mjösa Tower is firmly rooted in the Norwegian tradition of using wood in architecture to stand the test of time.

“We want to inspire others to build the same way,” says Øystein Elgsaas, architect and partner at Voll Arkitekter, the agency that designed the Mjösa Tower.

To design a tall building using wood was a positive challenge for Elgsaas. The load-bearing structure is similar to conventional buildings, but the dimensions of the elements are much larger than usual: The wooden columns were 60 × 60 centimetres on average, and the largest ones used in the corners were almost 60 × 150 centimetres.

The narrow, yet wide shape of the Mjösa Tower is ideal for hotel rooms.
“We had to find a narrow plan layout, which both provides room for different kinds of spaces and ensures the columns are not too dominant in the interior, but we achieved it,” says Elgsaas. The building won the prize for best mixed architecture at the 2018 New York Design Awards.

Both the “skeleton” and “skin” (i.e. the structure and facade) of the Mjösa Tower are made of wood. The structure consists of glulam columns, beams and diagonal members, which are well-suited to high-rise buildings as the large cross-sections can meet fire safety requirements. The first ten floors, with offices and hotel facilities, are made of prefabricated wooden elements – and that is where Kerto LVL Q-panels from Metsä Wood provide stiffness. Kerto LVL is combined with glulam.

The decks on the upper floors, with apartments, are made of concrete. This is due to the fact that the amount of swaying increases the higher you get in a building built of wood or concrete. The weight of the concrete makes the swaying slower and not as noticeable. The shafts for the elevators and staircases were made of CLT.

Kerto LVL Q-panels were easy to process as a component of the prefabricated wooden elements at Moelven Limtre’s factory. Some of the Q-panels were pre-cut and sanded beforehand at one our collaborator’s factories.

Kerto LVL is a lightweight and very straight material; thus, it guaranteed production without any delays. The quality of the product is very good,

Rune Abrahamsen, CEO at Moelven Limtre

“Kerto LVL is a lightweight and very straight material; thus, it guaranteed production without any delays. The quality of the product is very good,” says Rune Abrahamsen, CEO at Moelven Limtre. Cross-laminated Kerto LVL also has a great strength-to-weight ratio.

Lightness was a benefit in the assembly phase as well. As all elements were prefabricated and light to handle, the structure grew by almost one floor every week.

Frame with trusses, columns and beams

The main load-bearing structure consists of large-scale glulam trusses along the facades, as well as columns and beams inside the building. The trusses handle the global forces in the horizontal and vertical direction and give the building the required stiffness. You can see the structure from inside the building.

CLT is used for secondary load bearing in the staircases and elevator shafts and is not structurally connected to the glulam. Also Metsä Wood’s Kerto LVL Q-panels in the floor elements help in the secondary load bearing by transferring wind forces to the structure.

“As a glulam manufacturer, we strive to use our own material to the largest possible extent. However, Kerto LVL is a superior material for the top plate and end beams,” says Abrahamsen.

Stability with diagonal members

To ensure the stability of the Mjösa Tower, the bracing was ensured with huge diagonal cross-directional members across the facade.

“The trusses provide sufficient horizontal stiffness to handle the huge wind forces. The stiffness of the CLT core is inferior to the trusses, and is not a part of the lateral stabilisation,” says Abrahamsen.

The floor as one rigid plate

Thousands of steel screws, nails and plates were used in timber-to-timber and steel-to-timber connections to transfer the loads.

Double-threaded steel screws were used to connect the girders to the end beam, and screws also connected the end beam and the floor elements. Then a combination of nails and screws was needed to connect the floor elements to the supporting glulam beam. The floor elements were also connected to one another with nail plates.

“The connections were designed so that the prefabricated floor elements acted as one rigid plate,” says Abrahamsen.

Upgraded floor elements for fire-safety

The Mjösa Tower has been built according to strict fire safety regulations. The whole building has a sprinkler system. Untreated solid wood creates its own fire-resistant surface because the outermost layer chars when exposed to fire, protecting against further fire damage. To sum up, massive wooden structures manufactured in large dimensions are a good choice as they maintain the load-bearing capacity in case of fire.

In addition, each floor has been built as an individual compartment. The floor elements – including Kerto LVL and glulam – have a 90-minute fire resistance. These elements have been upgraded with brackets so fire cannot get to the hollow areas.

Long-term cooperation

Metsä Wood and Moelven have been cooperating for years. Abrahamsen appreciates both the quality and FSC certification of the raw material.

“Kerto LVL helped us to make the Mjösa Tower as sustainable as possible,” says Abrahamsen, who is looking forward to new high-rise projects. As cities become more densely populated, the demand for more sustainable construction is growing, and the use of wood will play an ever-increasing role.