Innovative office building

ARTICLE In Örebro a new office block is challenging the traditional approach to building. It is made of wood, with the exposed structure as a key element of the design.

Stepping out of Örebro Central Station, the warm wooden façade of Kvarteret Korsningen across the road quickly catches the eye, a calm oasis in a sea of busy roads and concrete buildings. A few years ago, the plot of land owned by the municipality consisted of a gravel car park with recycling bins.

»When we decided to develop this central, prominent site, we wanted a building of sound architectural quality, preferably a landmark that embraced innovation,« says Peder Hallkvist, City Architect in Örebro.

Reversed process

To achieve this, the municipality decided to take a bold approach and reverse the process by giving the land allocation to architects rather than a developer. The project attracted considerable attention in the industry, and eventually 13 architectural firms expressed an interest in participating. The municipality interviewed all of them to find out how they would approach the project, and Utopia was finally chosen. After an initial phase of workshops between the municipality and the architectural firm, Utopia came up with a proposal for a seven-storey office building where almost everything was made of wood – including the elevator shaft, stairs, interior surfaces and façade. Only the foundations were concrete.

»We knew from the beginning that we wanted to build in wood and see how far we could push it. We also felt that most new offices all look the same, with minimalist white surfaces and suspended ceilings, and little of the charm and identity that can be found in older offices. Having been handed the chance to decide so much for ourselves, we wanted to highlight the wooden structure and make it a central part of the building’s personality,« says Mattias Litström, creative director and lead architect at Utopia.

The design of the block began on the inside, starting with the exposed timber structure, based on a system of primary and secondary beams.

»We had an inspirational image of an old warehouse in New York with big wooden beams on the ceiling and exposed piping that was very rough and ready. Somewhere out of that came the idea of working with the wood as a raw surface and honestly portraying how the whole system is supported. It also prompted the early decision to completely avoid suspended ceilings and make the ceiling part of the architecture instead,« says Mattias Litström.

The next step was to take a closer look at the shape, which led the staircase to be moved out towards the façade.

Taking the stairs rather than the elevator

»The idea was to turn the concepts on their head and make it so that people would rather take the stairs than the elevator. Now you get great views of the city in several different directions as you move up and down through the building,« says Mattias Litström.

Externally, the building has been designed around the highly irregular plot and limited space of 1,200 square metres, with sides of different lengths to make the best possible use of the site.

»But at the rear, which backs onto a school, we took a slightly different approach. If we had built all the way out, the passage between the buildings would have felt very narrow. So instead, we’ve cantilevered the building higher up, giving us much more space than the plot would suggest,« says Mattias Litström.

Creative director Mattias Litström

The limited space and difficult location with busy roads on two sides of the building presented an additional challenge during the construction process.

»The conditions of the site meant that it was important to get the building up quickly. And thanks to a high degree of prefabrication, things went relatively smoothly. We bought the frame as a turnkey contract from Martinsons, who were able to get it in place quickly using their own team of installers. The façade contractor was Metus, and they did an amazing job. In addition to getting the façade done quickly, they were extremely careful to get every single detail correct, right down to the choice of screw heads in the façade,« says Jonas Hällgren, quality control engineer at Utopia.

Raising the bar further on the environmental side

But let us take a step back. The upended process at the start of the project meant that it was up to Utopia to find the right developer for the project, rather than the other way around, and they chose the real estate company and office developer Castellum.

»We thought they had a vision that fit in well with what we wanted to achieve. They also wanted to raise the bar further on the environmental side by certifying the building to the NollCO2 standard, which excited us,« says Mattias Litström.

NollCO2 certification requires net zero carbon emissions during the lifetime of the building, including materials, manufacturing and transportation during the construction process, the building’s energy use once it is completed, and end-of-life dismantling. For the architects, the main challenge posed by the certification was to find a good solution for the windows.

»The more windows you have, the more difficult it is to meet the carbon requirements. However, we didn’t want a façade with just a few small holes in it. I think we found a good balance in the end. We’ve added mirrored reflectors to the façade that deceive the eye, making the windows look much larger than they actually are,« adds Mattias.

Another measure that helps make the building climate-neutral is the solar panels on the roof, which actually generate some surplus energy over the course of a year. But the most important factor is the choice of materials.

»Choosing wood as the framing material has allowed us to significantly reduce the carbon footprint compared with using concrete,« says Jonas Hällgren.

The structure consists of a glulam post-and-beam system made of spruce. It was chosen quite early in the process and decided in consultation with the wood supplier Martinsons.

»We had extensive discussions about how to build the floor structure. The design we chose relies heavily on verticality, with the system comprising both primary and secondary beams. All the wooden load-bearing walls also required quite heavy metal fixings, which we wanted to keep hidden. So we added 13-millimetre-thick wall panels of CLT, making it wood on wood,« states Jonas.

Because the whole interior is exposed wood, the entire building is covered by a sprinkler system. Good acoustics were achieved with an impact sound absorbing floor covering, coupled with sound absorbing panels in the ceiling.

On the ground floor, the building has been designed as a mezzanine level with large glazed windows and a six-metre ceiling height, which helps to create an airy feeling. The same mezzanine feature is then repeated on the top floor, which has its own terrace. A delightful detail and key part of the exterior design is the wooden diagonals that run across the entire façade, forming a repeating diamond pattern. The timber elements of the façade use furfurylated wood, which also appears under the cantilevers that rest on top of the mezzanine level.

One important consideration for Castellum was flexibility and the ability to move, remove or add walls as the activities in the building change.

»We needed to build in a way that meant you could have everything from a whole floor of cellular offices to completely open floor plans or a combination of both. The challenge was how to achieve this in a system without a suspended ceiling. But in fact, it’s almost easier and creates greater freedom because all the utilities are visible and accessible in a whole different way,« comments Mattias Litström.

Sweden's first climate-neutral police station

No tenants had yet been found when the construction work began, but as the building progressed, a single tenant was secured for the entire building – the police. And so the building has become Örebro’s newest police station, complementing the previous station nearby as Sweden’s first climate-neutral police station, and probably the country’s only timber one.

»We’re very pleased with the result. Both with the architectural design itself and with the debate the building has generated about how to build in new and innovative ways,« says Peder Hallkvist.

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