Utilization of residual concrete for water gutters in Trælasten project

It all started with an idea from Nordstern’s Project Director, Allan Brandt. He proposed using excess concrete from element assembly to cast concrete gutters, as a replacement for the planned corten steel rainwater gutters. Typically, this surplus concrete would be crushed and used as road fill. Allan saw the opportunity to save resources while creating a functional product.

Thomas Kröll from Vandkunsten Architects, who designed both the buildings and the landscape for Trælasten, quickly embraced the idea. They began evaluating the pros and cons of substituting corten steel with surplus concrete. Local planning regulations for Trælasten require rainwater from buildings to be conveyed in open gutters to a central drainage system. It was important for the project team to design the concrete gutters with precise cross-sections and water flow, so that they could match the functionality of steel gutters.

“Nordstern was incredibly proactive. They immediately cast the first prototype, confirming the potential we saw in the solution. This approach opens new ways to reduce waste and lower the CO2 footprint, and it should be further developed to minimize material waste on construction sites,” says architect Thomas Kröll.

In a previous project within Trælasten, Teglgården—also designed by Vandkunsten—corten steel gutters were used. This provided Thomas Kröll with a basis to compare the material choices for Trægården. By analyzing the two solutions, the architects were able to gain insight into the impact of switching to surplus concrete on the landscape design and CO2 emissions.

Slow, but effective production

The concrete gutters are being produced through a slow but resource-saving process that extend over a year while the carcass of Trælasten is built. Allan Brandt explains:

“We’re casting a total of 150 meters of gutters. Each time we pour concrete on-site, there’s half to a full cubic meter of surplus concrete we can use for the gutters. Instead of discarding the excess, we pour it into molds and cast one to two elements at a time.”

Advantages of the material shift

By analyzing the durability and CO2 footprint of the concrete gutters, the architects identified clear advantages in using concrete over corten steel. The results showed that concrete gutters emit 15.7 kg CO2 equivalents per meter, whereas corten steel gutters emit 134.1 kg CO2 equivalents per meter. This material shift reduces CO2 emissions by 88%.

The fact that the concrete is already available as a surplus material eliminates the need for additional production or transportation. Furthermore, it demonstrates how waste can be minimized, and new uses for existing resources can be identified—a strategy the project team plans to continue in future developments.