Hybrid sandwich wall element

​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 sandwich wall element 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.

Innovation in partnership

A great opportunity for element producers

Metsä Wood partnered 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 saw 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 will be 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. 

These designs and the hybrid sandwich wall element design are already available at the Open Source Wood platform, which aims at facilitating knowledge sharing, co-creation and growth in modular wood construction.


Technical properties

Benefits of replacing the internal 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 load-bearing internal 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.

Values guide Metsä Group's operations 

When the building is constructed, the loads are transferred from the external wall to the concrete structure to stiffen the building.

The new element also provides effective insulation. By building a hybrid element from wood and concrete, the U-value can be 20% better.

Sustainable construction

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 light load. The light elements are also faster to lift," says Björman.

He also points out that new easy-to-produce construction solutions are needed to turn the industry in a more sustainable direction.

"Around one million square metres of concrete wall elements are produced annually in Finland. Their load-bearing core creates 45,000 tons of CO2 emissions. If all concrete walls were replaced with hybrid sandwich wall elements, CO2 emissions would decrease by 30,000 tons a year and 95,000 tons of carbon would be stored," highlights Björman.

Rauma Sawmill

The first hybrid sandwich elements in use

Metsä Fibre's new Rauma sawmill is the first construction project where the hybrid sandwich wall elements will be used. The hybrid wall elements will be installed in June.

  • The Rauma pine sawmill is the largest sawmill investment, EUR 200 million, ever in Finland.
  • The new sawmill will be a forerunner in technology and efficiency. For example, machine vision in different stages of the saw process is a significant new development.
  • Skanska is responsible for constructing the mill.
  • The sawmill will produce around 750,000 cubic metres of pine sawn timber annually.
  • Production is set to begin during the third quarter of 2022.