LTU students win icy challenge

How do you best prove that sustainable construction truly makes a difference? With an icy experiment! Civil engineering students at Luleå University of Technology claimed victory in Sweden's first-ever Ice Box Challenge – a competition to design and build an energy-efficient mini-house that best preserves a one-tonne block of ice.

"It feels absolutely amazing to win! It’s been great to represent Luleå University of Technology in this competition. We’re an incredible team that has accomplished this together, and I’m incredibly proud of our group and everything we’ve achieved," says Valentin Romero, and student in MSc in Architectural Engineering at Luleå University of Technology and project leader for the winning LTU team, Sub-Zero Studio.

The houses were filled with large ice blocks

The Ice Box Challenge is a global initiative that has been held in over 17 cities worldwide over the past 18 years. Its aim is to raise awareness of sustainable construction and energy efficiency. Now, IG Passivhus Sverige has brought this challenge to Sweden, where teams compete to build the most sustainable and energy-efficient mini-house.

The competition, which integrates five of the UN’s Sustainable Development Goals, is as simple as it is ingenious: Two identical structures are built—one following standard national energy regulations, and the other designed to be a sustainable, energy-efficient, and circular house with minimal environmental impact. Both are filled with ice and left outside for several weeks.

The winning houses will be recycled

At the competition’s conclusion, culminating in a ceremony on 6 June 2025, the mini-houses were opened to measure how much ice had melted in each—a clear demonstration of the difference in insulation and energy efficiency. The results clearly illustrate how different building standards affect energy consumption and sustainability.

The jury assessed the teams based on several criteria, including the design of the structures, materials used, ease of construction and dismantling, reuse of the structures post-competition, the amount of ice remaining in the passive house compared to the standard-built structure, presentation, marketing, and teamwork.

"The biggest challenge was balancing design, buildability, and dismantlability—bringing everything together as a whole. Solving one problem often leads to another, so it was a hands-on experience that involved all disciplines within the project. We had to apply every aspect of our education and weave them together", says Christoffer von Rosen, student in MSc in Architectural Engineering at Luleå University of Technology.

Now, Sub-Zero Studio’s passive house and standard-built box will be reused as field huts in Norrbotten. The traditional tent surrounding the passive house will be repurposed as a wind shelter at Hertsö kullar in Luleå.

Participants in the winning LTU team, Sub-Zero Studio: Elvira Lundell Wallin, Martin Engsvik Stomberg, Gusten Wendelhag, Christoffer von Rosen, Dag Virtala, Hugo Ottesen, Anton Wängestam Blomberg, Valentin Romero and Sebastian Rosberger.