Kaj 16 Gothenburg

The 37500 square metre project is situated on the edge of the river. Kaj 16 forms a focus point of the wider neighborhood development. The area, called Lilla Bommen, will go through a major facelift. New street plans will open the waterfront and make the quays accessible. When completed, there will be workplaces and housing for approximately 25 000 people in the area.

Our client Vasakronan is one of Sweden’s largest property companies with 168 properties with a total area of 2.4 million sqm. By 2030 Vasakronan aims to have an entirely climate neutral value chain.

In the Kaj 16 project Ramboll partners with architects at Dorte Mandrup A/S and Bisgaard landscape.

Hybrid solution

The project team were challenged with an ambitious carbon profile including reuse of building materials from the existing structure and a timber structure and façade. The building will be LEED platinum certified.

The project offers a case study in how far we have come with timber buildings. The developer originally wanted the entire building to be made from timber, but Ramboll engineers demonstrated how a hybrid solution would be better.

“For Kaj 16, the first thing we did was to create ten different models based on different materials to assess the carbon impact of each: a traditional concrete building, one in steel, and so on. We found what the developer had originally thought would be the most sustainable – a building solely made from timber – did not perform as well as a hybrid building,” says Riccardo Pedroni, associate and timber specialist on the Kaj 16 project.

The team found that the best solution was to use concrete for the cores and podium levels, and timber for the remaining superstructure – beams, columns, and slabs. If the cores had been made from timber, they would have been too large, leading to an inefficient use of materials.

The findings corroborated those of a recent Ramboll study that screened all own timber projects in the world, and concluded that above a certain height, hybrid buildings perform better.

“Timber excels in buildings up to 15-20 stories, but once we reach heights above, other materials are likely to be better. So, it’s not a one-size-fits-all,” Frank Schwartz, head of department & spearhead director, high-rise buildings Denmark, explains.

At Kaj 16 material could be reused from the sites original structure reducing carbon impact and mitigating inherent weak points of building with timber.

“We took the existing concrete structure, which was a somewhat out-dated 1960s build, and crushed the concrete down, separated it from the rebars and reused it in the new concrete mix for the basement and cores,” explains Frank Schwartz.

“We are also planning to place recycled small dry aggregates on top of the concrete deck to improve the acoustics and vibration response of the deck. In doing so, we also avoid placing wet concrete on top of the timber, mitigating one of timber’s weak points.”

“We can make buildings in timber, steel, concrete, or 200 different hybrids. But by using data, and modelling different solutions, we can ensure the finished building is actually better for the specific location,” he adds.