Wooden residential buildings made with Kerto LVL elements

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  • Offsite construction, Kerto LVL, Multi-storey building

The 'Kerto® LVL residential buildings’ in Turku – constructed fast from wooden elements

​’The Kerto LVL buildings’ – the Linnanfältti residential area of wooden three- and four-storey apartment buildings, were constructed fast in Turku. The wooden residential buildings were built using elements based on Metsä Wood’s Kerto LVL (laminated veneer lumber) products, enabling fast, light and green construction.

City of Turku has enabled construction actors to experiment wood construction and build an urban area. The goal was to give new life to an old industrial milieu with different kinds of housing opportunities and services. The old wooden houses are now next to four more recent wooden residential buildings with 128 cozy homes.

"The project has been successful, and visitors call the area pleasant. It is a distinctive area with colourful buildings, quarter courtyards and soon also public art", says Mika Rajala, Architect at the City of Turku. He leads the steering group of the project.

Rajala points out that in Linnanfältti area wood construction means that the structures and facades of the buildings are made from wood.

Linnanfältti is situated close to Turku Castle and the Port of Turku, very close to the city centre. It is one of the largest wooden apartment building construction projects in Finland. Some 1,500 people will have homes there.

Element production and off-site construction

VVR Wood has done the structural planning and built the elements at their factory in Heinola. Kerto LVL S-beams, T-studs and Q-panels are used in the wall elements, Kerto LVL S-beams and Q-panels in the floor elements, and Kerto LVL S-beams and Q-panels in the roof elements.

VVR Wood has become Finland’s biggest supplier of wooden element apartment buildings. The CEO Tero Vesanen believes that the world is at a turning point with wood construction. Element producers exist and constructors have gained experience and seen the impacts on productivity.

”As the construction work relocates from site to factory, the quality increases in dry conditions, work gets done more efficiently and waste is minimized. A residential building constructed from Kerto LVL elements can rise in less than half the time compared to a similar kind of concrete building”, says Vesanen and adds that wood elements are 4-5 times lighter than concrete elements.

The construction of the third four-storey apartment building in Linnanfältti went fast.

”It took one week to build each floor. As the wooden elements are light, assembly has been done with a bridge crane, which is integrated to a weather protection cover,” says Jari Granqvist, Foreman responsible for wooden residential construction at NCC.

Granqvist adds that the cover has been a handy solution to keep the building and wooden elements dry. The cover has also made construction faster as both the cover and crane can be lifted. The construction team has always had the right height according to the construction phase.

Prefabricated elements to handle the loads

The wooden frame of the multi-storey residential buildings consists of load-bearing walls. In the wall elements, the Kerto LVL S-beams and Kerto LVL T-studs are connected to the top and bottom chords made of Kerto LVL Q-panels. These elements are also insulated.

The top panels of the intermediate floor elements form a stiff plate, which transfers the loads to the walls. These structurally glued, ETA-approved Kerto-Ripa elements contain Kerto LVL S-beams as webs and flanges, Kerto LVL Q-panels on top and in endbeams, and an insulation layer. Kerto-Ripa is a ready to-use design system developed by Metsä Wood.

The roof elements, containing Kerto LVL S-beams, Q-panels and insulation, and walls stiffen the building. The roof elements transfer the snow and wind loads through the walls to the concrete foundation.

Strong connections

All of the connection solutions of the residential building reinforce the loads needed. Screws are used in timber-to-timber-connections except the connections between intermediate floor and wall elements, which are nailed.

It was easy to make the connections as Kerto LVL has great workability, yet it is a very strong and rigid material.

Fire resistant material

The wooden multi-storey residential building complies to Finnish fire-safety norms.

The Kerto LVL structures have 60 minutes resistance to fire rating, and construction materials include gypsum, insulation and fire retardant panels in staircases and exits.

In the event of fire Kerto LVL’s surface becomes charred, which protects and insulates the product, thus slowing down the charring.

The building has also been divided individual compartments and is sprinkled.

Smooth cooperation

VVR Wood and Metsä Wood have cooperated a lot as VVR Wood is one of the producers of elements based on Metsä Wood’s Kerto-Ripa design system. NCC was a new partner to VVR Wood.

“Cooperation with all parties went well. The key has been the careful synchronization of Kerto LVL deliveries, Kerto LVL element production at our factory and assembly on-site. With this experience we are ready for new projects,” says Vesanen.