The Feldballe School extension in Denmark is a carbon negative lesson in sustainability

As the world transitions towards a climate crisis urgency, the building industry, amongst others, faces a large responsibility—to design and construct buildings that help fight climate change instead of furthering it. Copenhagen-based Henning Larsen responds to these challenges with a carbon negative extension to the Feldballe School in Rønde, Denmark. Built primarily with wood and straw, the school architecture is a scalable building that captures more carbon than it emits.

The fact that the extension is built to host science classes for a generation growing up with the weight of the climate crisis forms the evident inspiration behind the material choices and sustainability of the design. The studio uses bio-based materials as superior alternatives to concrete, brick, and steel, as they are fire-safe, free of toxic chemicals, and boast efficient insulation to provide a comfortable indoor climate.

The studio also partnered with EcoCocon, a Danish philanthropic organisation, to engineer a panel system of compressed straw, a timber roof with solar panels, untreated plywood built-in furniture, and a ventilation system made of eelgrass—common seaweed found along seashores in the Northern Hemisphere.

The form of the building with spacious and high-ceiling rooms alleviates the need for ventilation ducts and suspended ceilings. It is also designed for easy disassembly and reassembly. This promotes flexibility and reuse while also creating circumstances for easy repair and reinstallation. 

Danish architecture studio Henning Larsen expertly uses a natural set of materials combined with an intelligently drawn up design to create architecture that is considerate to its residents and the context in which it resides, without compromising on the architectural identity of the project.

In conversation with STIR, Magnus Reffs Kramhøft, lead design architect at Henning Larsen, expands on the design process of the carbon negative building.

Pooja Suresh Hollannavar: You talk about using an 'uncompromisable material strategy' in the design. Could you elaborate on that?

Magnus Reffs Kramhøft: The conscious use of materials is at the core of the Feldballe School extension. An uncompromisable material strategy was one of the dogmas of the project; a shared ambition with the client that resulted in the school extension being built entirely of bio-based materials, with no toxic chemical treatment.

Pooja: While most of us are aware of what 'carbon neutral' means, 'carbon negative' is a relatively new term, especially in the context of the building industry. Could you use this project to exemplify what it means in a bit more detail? 

Magnus: Bio-based materials, such as trees and straw, harvest/sequester carbon as they grow. When we use these materials in buildings, we preserve them and store this carbon, preventing the CO2 from being released into the atmosphere: the bio-based building effectively becomes a CO2 bank. Carbon negative means that more carbon is stored than carbon emitted in the production of the materials, the construction of the school and in the operational phase of the building’s total lifespan (calculated as 50 years). Therefore, the only way a project in fact becomes carbon negative is when we know for certain how all its materials and components have been treated and ensure their end-of-life and that they can be repurposed.

Pooja: The school is also designed to be disassembled and reassembled if needed. Why was this feature important? Wouldn’t the disassembly and reassembly add to the carbon footprint of the project?

Magnus: Annual construction waste is expected to reach 2.2 billion tons globally, by 2025. That is because many conventional construction materials and components are not designed to be disassembled and are bound to a linear production model. Put simply, designing for disassembly means prioritising circularity so that materials and building components can be reused instead of ending their life in a landfill, or being burned and emitting their CO2 into the atmosphere.

Designing for disassembly is not something that lets out more carbon. It does not make the building more complex. It’s simply a mindset, a way of preparing the construction that will make it easier to use the parts again in the future. Reusing materials is the most sustainable option we currently have. The carbon footprint caused by reusing materials is much lower than using one that is new. It is not the intention of the Feldballe school to be disassembled completely and rebuilt. We hope that the building can be taken down piece by piece, so the materials can be held in circular loops and serve as new materials for future buildings, when this particular building is not needed anymore or a change in functionality is needed. 

Pooja: This comes across as a small-scale—big impact project. Throughout the design process of creating a carbon-negative building, did you ever view this project as an experiment that can lead to more such environmentally friendly structures, but on a larger scale?

Magnus: Yes, absolutely. This project has shown us that a green transition is within reach. By starting with a small project, we gathered an immense amount of new knowledge that we can apply to future projects. Though small in scale, the school shows the potential that arises when an uncompromising material strategy is adopted, and accountability is embraced as a catalyst for design. Now we would love to do much more and at a much larger scale. The more square metres are built this way, the less CO2 we emit in the building industry. Our goal is to push the whole industry in a more sustainable direction, we have a responsibility to do so. Whilst this construction system is not the only answer, it’s a central one in the search for a sustainable transition.

Pooja: What was your biggest challenge when designing and executing this building?

Magnus: The biggest challenge was that a lot of the project team was working on something they have never tried before. In the beginning, this required a more diligent and slightly slower process than expected as we dealt with uncertainty but in the end, we had a simple, fast, and logical construction process. Next time, of course, it will be.

Project Details

Name: Feldballe School Extension
Built Up Area: 250 sqm
Location: Rønde, Denmark 
Year of completion: 2022
Architect: Henning Larsen
Contractor: Høgh & Sønberg 
Engineer: Reeholm & Bredahl