The six-storey Lumber 4 office block in Kristiansand, Norway, is a streamlined building with a strong identity. The green, concave façade elements are inspired by the rolling green North Sea just outside – as well as symbolising the building’s sustainability profile.
In a former industrial area by the sea, a new district of housing, offices and shops is taking shape in the centre of Kristiansand. It is also home to the city’s first large wooden office building, Lumber 4, and it is a building that will not go unnoticed. The façade comprises an undulating patchwork of green, concave façade elements that protrude above the rounded entrance level.
»Since Nekkar, the largest tenant and part of the same group as the client Skeie Eiendom, works in green energy, we wanted to create an expressive façade in wood that says the building has been created for a new, greener age. By setting the ground floor back and making it circular, we were able to achieve a lighter feel, while at the same time exposing the load-bearing structures and clearly showing that they’re made of wood,« says Jørgen Tycho, lead architect at Oslotre, which was responsible for both the architecture and the timber structures.
Wood construction
Oslotre was chosen because of an interesting article that the client had read about their demountable office building Hasletre in Oslo.
»By then they already had a design for a steel and concrete building so they asked if we could design a timber building for the same site, without it costing more than the other option. The starting point was that it had to comply with the basic requirements of Norwegian building standard TEK-17,« says Jørgen Tycho.
The load-bearing structure of Lumber 4 consists of double beams and glulam columns. The columns go all the way down to the bottom floor, where diagonal beams help to absorb the forces. The hybrid floor system used between the floors comprises two-thirds CLT and one-third concrete. The concrete takes up the compressive forces and the wood handles the tensile stresses.
»It’s an excellent, cost-effective solution that meets fire and acoustic standards and gives you the best of both materials. It also means you can keep the dimensions down, resulting in very slender structures. When we initially used it, we were the first in the world to do so on a large-scale build. We’ve chosen it several times since then and know that it works well,« says Jørgen Tycho.
Using just wood when possible
However, he points out that Oslotre prefers to use just wood wherever possible.
»In this case, we had to take into account the car park under the building. And with such a long span, it was more efficient to use a hybrid floor than just wood.«
The lift and stairwell shared with the neighbouring building are also steel and concrete.
»If they hadn’t already existed, we would have made them out of mass timber – we’ll do that with the next building we construct in the area. But because our hands were tied in this instance, we used the lift and stairwell to help stabilise the building,« he says.
CLT and glulam
Spruce CLT and glulam make up the building’s load-bearing structures, while the façade elements are heartwood pine, painted with green tar.
»We usually go for untreated heartwood pine, which turns grey over time, but here the green will fade instead. However, since the eaves above the concave elements are straight, darker semicircles will form beneath them, meaning that the façade will only become more dynamic, expressive and alive as the years go by,« says Jørgen.
Inside, the walls are mainly clad in white stained spruce panelling, with the exception of some lightweight walls in plaster. Between floors three and four there is also an atrium with an internal staircase made of CLT.
»We’ve created a very flexible design, both horizontally and vertically, making it easy to move the interior walls or open things up between floors,« Jørgen adds.
The tenant is the green energy company Nekkar, which moved in last March.
»We’re very pleased with our new office, and the indoor climate and acoustics in particular. The combination of wood and light-coloured carpets creates peace and quiet and a warm feeling. And the ventilation ducts on the ceiling are actually quite nice. When you hide them behind a tiled ceiling, you get a bit of a hospital vibe. This feels more industrial, which fits in well with the setting,« says Ole Falk Hansen, CEO of Nekkar.
Apart from the ground floor, which is rented out to a furniture store, the building is all office space, and most of the tenants are tech companies like Nekkar.
»The building was 90 per cent leased even before it was completed, and now it’s fully occupied. There are currently five tenants,« says Jørgen Tycho.
Advantages building with wood
The build itself progressed at record speed, says Magnus Homme Jortveit, project manager for contractor VEF. This is the company’s second major wood construction project with Oslotre.
»The design phase takes a little longer when working in wood, but once you get going it’s an extremely effective and efficient process. In this case, it took six weeks to erect the entire six-storey building. If it had been steel and concrete, it would probably have taken four months,« he adds.
And that is not the only advantage.
»Our employees are much happier working with wood. There is less drilling, hammering and noise, less disruption and a more pleasant climate in general. We haven’t checked the figures, but I feel that sick leave has decreased. Plus there’s less waste,« says Magnus.
Another advantage that both he and Jørgen Tycho point out is sustainability.
»We’ve been able to cut carbon emissions by 53 per cent compared with a traditional building, which has contributed to the building’s BREEAM certification with a rating of Very Good,« says Jørgen Tycho.
Working on the next wood project
He and his colleagues at Oslotre are now working on the next major project for the same client and in the same neighbourhood: Lumber 5. This time it is a seven-storey office building made entirely of wood and twice the size of Lumber 4. Construction is scheduled to begin in the spring, with completion in 2025.
»I believe wooden architecture is the architecture of the future, with everything built in 3D models, prefabricated in factories and then assembled on site. This gives us a construction method that’s much more precise, generates less waste and fewer errors, and is much faster. We’re already seeing wood construction becoming very competitive with concrete and steel. And it’s only going to get better. Wood construction in industrialised form is still a relatively young method at around 25 years, compared with 150 years for steel and concrete,« says Jørgen.
For Oslotre, the story began in 2010, with a CLT factory. Jørgen Tycho explains that at the time, CLT had a bad reputation in Norway for being both defective and expensive. So they set up an architecture and engineering company to learn the design side and an assembly team to do the building.
»That way we learnt about everything that happens before and during production, because the fault was not in the material. Wood, by its very nature, has few defects. The problem was that architects and engineers were unable to design in wood and construction companies didn’t know how to build in wood. Our philosophy is that all the architects and engineers who work with us should go out to the site so they understand what they’re designing. On site, you get a much clearer idea of what makes sense and what doesn’t.«
The company sold the CLT factory in 2015 to focus on architecture and construction. And it proved to be a sound move.
»Despite the economic situation, we have a lot of work on, and are currently recruiting more employees,« says Jørgen