20 unique floors stand tall in the up-and-coming South Harbour neighbourhood of Aarhus

The building, TRÆ, is innovative in a number of ways -- especially when it comes to material choices. A large amount of recycled materials have been used for both the interior and the exterior and three floors are dedicated to experimentation with new materials that could provide a further boost for the green agenda.


There is a great desire to build at the South Harbour in Aarhus, Denmark - an old port and industrial neighbourhood that is being transformed into an urban business area with space for art and culture, urban living and social diversity. New buildings such as Danske Bank's Aarhus office, the new headquarters of Jyllands-Posten and an expansion to Filmbyen have already been completed.

But the South Harbour neighbourhood is far from finished. 

PFA Pension is the contracting authority for Denmark's tallest wooden building, TRÆ, which will be a unique feature of the area, both in terms of the concept and the physical design. Kilden & Hindby has developed the project in collaboration with Lendager Arkitekter and the consulting engineering firm Artelia Group.

TRÆ will stand 78 metres high and will include 20 floors that will primarily be used for office premises and co-working space. The building is expected to be ready towards the end of 2024.

The ambition for TRÆ is to disrupt the way the industry currently builds, by primarily using wood and recycled materials. Nevertheless, TRÆ is a hybrid building and concrete is also used in selected areas.

"TRÆ will demonstrate that it is possible to construct tall buildings using wood. We are also using recycled and bio-based materials in a bid to achieve a less carbon-intensive building, which is necessary in order to fulfil the Paris Agreement. TRÆ is therefore an example of a way forward for the construction industry that is less damaging to the climate," says Kasper Bach Joahnnsen, Chief Advisor at Artelia.

How far can you get with recycled materials?

Henrik Kjærgaard-Phillipsen is the Project Director at the urban development firm Kilden & Hindby, which has developed some of the major projects in Aarhus, including Lighthouse, Pakhusene, AARhus, Bassin 7 and Æggepakkeriet at Godsbanen.

"Everyone talks about sustainability in the construction industry, but there hadn't been enough action to meet the green ambitions, so we decided to "rip the plaster off" and see just how far you can get with recycled materials. We joined forces with Anders Lendager, who had some excellent ideas and experiences from sustainable buildings, and combined with our experience in large-scale builds, we had created a great team for the task.

Life cycle assessments (LCA), combined with common sense and faith in our gut feelings, have been important tools throughout the entire construction process.

Old wind turbine blades and roof panels from Herlev

As a special feature, old wind turbine blades are used for sun shielding on the exterior of the building. Wind turbine blades last for around 20-25 years in operation and often end up in landfill afterwards.

"For a long time, it has been difficult to figure out how wind turbine blades could be recycled, but they are strong and withstand the most extreme weather conditions. That is why we decided we wanted to learn more about the material. DBI conducted several fire tests on full-scale facade models and these have now been approved," Henrik Kjærgaard-Phillipsen explains.

Originally, the desire was for TRÆ to have a wood-clad facade, but this was not possible due to fire requirements and the durability of fire impregnation for such a high building. Instead, the facade has been clad in aluminium from former roof panels from a housing association in Herlev. Even though the material has been recycled, the anticipated remaining service life is between 80 and 100 years.

"The panels are patinated and you can see the old mounting holes. They have been supplemented using discarded aluminium panels from a different range and this creates a distinct design pattern on the facade. This type of aesthetic differs from the many other new buildings that are popping up throughout the city and I look forward to hearing what people think, as well as the accompanying discussion that will undoubtedly take place," says Kjærgaard-Phillipsen.

"The process of figuring out what the building would look like was lengthy, as it is different from normal. For this reason, we have also collaborated with the City of Aarhus' architect, who has participated in several workshops," he adds.

More obstacles associated with recycled materials

There are also countless examples of the use of recycled materials inside the building. Glass, wood from industry and ceiling panels made from recycled plastic bottles have been used, as well as light fixtures from Netto stores that have been upcycled and fitted with LED lamps.

Kasper Bach Johannsen, Chief Advisor at Artelia, explains that there are several barriers when you set out to use recycled materials in large-scale buildings:

"Naturally, the fire requirements for multi-storey buildings are strict. Materials must therefore satisfy the appropriate fire classes. For example, for TRÆ, we needed to have only 20 per cent visible wooden surfaces inside, as the rest had to meet the applicable fire classes. Documentation from manufacturers is therefore essential."

Another barrier is linked to warranties for the selected materials.

"When you buy a new product, there will automatically be a warranty, but that is not the case for recycled products -- at least not yet. We therefore had to make sure that the contracting authority was not planning to replace any products after just a few years of use. Nevertheless, several manufacturers have launched take-back schemes, under which you can return old products and they will inspect them and offer a warranty for the products," Bach Johannsen explains.

Another barrier noted by Bach Johannsen is the possible constituents and degassing from the materials:

"With one-to-one recycling, we rely on those who dismantle the material to have carried out testing and environmental screening to check for any heavy metals, etc. In order to be confident and reassure the contracting authority that there will be no toxins or degassing from the product, we need to carry out our own random checks on the products."

The Living Lab experiment

TRÆ will boast a co-working space called Living Lab, which will span three floors. Each floor has its own theme. One floor is constructed exclusively using recycled materials. The second floor has been constructed exclusively using bio-based materials such as wood and the third floor is an upcycled floor on which recycled materials are given a new lease of life.

"The Living Lab experiment has allowed us to play around a little and test new materials for e.g. furniture and fittings, partition walls and more. There are some really interesting products available on the market, but a number of these were unable to meet the documentation requirements for e.g. a healthy indoor climate. We are, however, extremely pleased with the materials we have chosen," Bach Johannsen says, before adding:

"On the recycled floor, we will use recycled Troldtekt acoustic panels. Troldtekt uses durable materials with excellent documentation and the recycled panels perform well from an LCA perspective.

The Troldtekt acoustic panels were supplied by Greendozer, which is a platform for the sale of recycled materials.

The flooring used on this floor originated from a demolished apartment building from Gellerupparken in Aarhus.

Kjærgaard-Phillipsen explains that there is a difference between experimenting on 300 sqm compared to 15,000 sqm.

"We are now testing selected new products and methods in the "Living Lab". This requires everyone to be positive and brave. We have gained a wealth of experience from the TRÆ project. The negative experiences can be avoided in the future, while the positive experiences can be reused for other buildings and on an even larger scale.

When the floors are put into use, we will carry out indoor climate measurements and the use of the spaces will also be studied by anthropologists."


  • TRÆ is a new office building situated at the South Harbour in Aarhus. The project is expected to be ready by the end of 2024.
  • It will consist of a 78 metre high building with 20 floors and two smaller buildings of six floors each.
  • The contracting authority is PFA and the project has been developed by Kilden & Hindby in collaboration with Lendager Arkitekter. The consulting engineer for the project is Artelia.