Hybrid construction offers construction companies more sustainable buildings without changing the current way of construction. Metsä Wood and its partners have designed a hybrid sandwich wall element which will renew offsite construction. The innovation combines concrete with Kerto® LVL (laminated veneer lumber). The first construction project to use the elements is Metsä Fibre’s Rauma sawmill.

The need for more sustainable solutions is acute, because construction causes 30% of all CO₂ emissions. Combining concrete and Kerto LVL, the hybrid sandwich wall elements offer an easy way to replace typical concrete sandwich elements, the popular wall element in residential multi-storey buildings in Nordic countries. Most importantly, the innovation guarantees efficient construction.

“The hybrid construction helps to increase the share of wood to build more sustainable buildings efficiently. This joint development is our effort to support the construction industry,” says Jussi Björman, Director at Metsä Wood. He is responsible for business development in construction.

Björman gives examples: the connections between the wall elements are similar and so are the lifting loops compared to the ones used in concrete elements.

A great opportunity for element producers

Metsä Wood collaborated with JM-Rakenne Oy, Peikko Oy, and Arkta-Reponen Oy to design the optimal hybrid sandwich wall element, which can be used in residential, office or industrial multi-storey buildings. Lipa-Betoni recognised the potential of the hybrid elements immediately when Metsä Wood approached them.

"The hybrid sandwich wall element is a great opportunity. We look for a new market with a product, which can be used in the same way as concrete sandwich elements," says Satu Lipsanen, CEO of Lipa-Betoni.

Lipsanen is pleased with the cooperation, where Lipa-Betoni's concrete knowhow meets Metsä Wood's wood experience. The goal was to design a practical element, which is easy to produce and use in construction. The first hybrid sandwich wall elements were produced at Lipa-Betoni's factory in Pieksämäki, Finland, for Metsä Fibre's Rauma sawmill construction project.

On a global scale, the potential is huge.

"Metsä Wood currently works with European and Australian companies to produce similar ideas that fit the local way of construction. Half a dozen designs are being prepared for publication this year," says Björman.

Benefits of replacing the core panel with Kerto LVL

The starting point for the new element design was a common residential seven-storey building with a concrete structure including hollow-core slabs and party walls made from concrete as well.

In the hybrid sandwich wall panel, the internal load-bearing core panel is replaced with a Kerto LVL Q-panel. Otherwise, the structure of the element remains the same; the façade is made from concrete and the element has an insulation layer.

"As a material, Kerto LVL is very comparable with concrete. The compressive strength of the Kerto LVL panel is as high as that of C25 concrete, 26 MPa. Also, the tensile strength of the panel is at the same level, whereas in concrete it is 10% of the compressive strength without steel reinforcement. In a hybrid sandwich element, the reinforcement is needed only in the façade," says Ari Mättö, Structural Designer of JM-Rakenne Oy.

The combination of concrete and Kerto LVL increases sustainability by decreasing emissions

"As Kerto LVL is a light material, the hybrid sandwich wall elements will be faster to produce at the factory and transport to the site, and even the transport emissions will decrease due to the lighter load," says Björman. He also points out that new easy-to-produce construction solutions are needed to turn the industry in a more sustainable direction.

Skanska, the constructor of Metsä Fibre’s new Rauma sawmill, has set up ambitious goal for itself as it aims to be carbon neutral globally by 2045. This has led the company to provide low-carbon or carbon neutral life-time solutions to its customers. 

“We are happy to try new, innovative things and partnerships, and the use of these new hybrid sandwich elements in the new Rauma sawmill is a great example of this kind of cooperation. The use of hybrid elements reduces the amount of concrete, and the elements are also lighter than typical elements,” says Ilkka Romo, Director of the Productivity and Quality Unit at Skanska.

“The assembly of the hybrid sandwich wall elements has been similar to the usual concrete sandwich elements. Their lighter weight can bring savings in a large construction project,” says Petri Puputti, Construction Manager, Skanska. 

Romo foresees that wood construction will increase over the next couple of years, and there is already now more demand. The forms of wood construction and their impact on business and customer wishes are under review. 

“Hybrid construction allows to reduce construction related CO₂ emissions and in addition it created long term carbon storage. For example, 30,000 tons CO₂ eq. emission reduction and 95,000 tons of carbon storage, in CO₂ eq., can be achieved when one million square meters of hybrid sandwich elements are used,” highlights Björman.

Rauma sawmill

Metsä Fibre's new Rauma sawmill is the largest sawmill investment, EUR 200 million, ever in Finland. It is also the first construction project where the hybrid sandwich wall elements are used. The elements, which are used in the sawmill’s log sorting building were installed in September 2021. The installation for the first floor, 100 m², of the building was successful and it took five hours to assemble the elements.