Contractors have completed the frame of an 85.4 m tall timber building about 60 miles north of Norway's capitol, Oslo.

Artist's view of the Mjos Tower in Norway.The Mjos Tower (Mjøstårnet) had its last beam hoisted into place by a crane in early September. The building uses glue-laminated timber (glulam) that its developers say will burn only when continuously exposed to flames. When it opens in March 2019, the tower will surpass a 49 m timber building, also in Norway, that ranked as one of the world’s tallest wooden buildings.

Glulam is wood that has been planed and then glued together in a manufacturing facility to form columns and beams.

(Read "How Wood Can be Used to Create Large Buildings.")

The Mjos Tower will include apartments, an indoor swimming pool, a hotel, offices, a restaurant and common areas. It was originally supposed to be 81 m high, but a rooftop pergola added another 4.4 m. The addition lifts it higher than the HoHo tower (84 meters), being built in Vienna, Austria.

Beams for the Norwegian building arrived fully processed at the building site where a crane lifted them into place with no need for external scaffolding. Engineering firm Moelven raised as many as five floors at a time.

Fire Safety

Engineers says that the glulam structures that are used in the building are large enough to retain their load-bearing ability in the event of a burnout fire. In the event of a fire the members are expected to develop an ash coating that will stop a fire from spreading.

The developers say that the weakest point in a timber structure in the event of fire is the steel used for the connections in the structure. The glulam structure is built with fire strips to protect the steel sheets and dowels in the junctions and joints. The fire strips consist of a material that expands 20 times at 150° C. The strips are intended to protect the steel from the temperature rise, close openings and prevent fire from spreading.

What's more, each individual floor, apartment and hotel room is designed to act as a separate fire cell that is expected to keep a fire from spreading. As an extra precaution, outer wall elements have been treated with a fire retardant material.