As of late, Henning Larsen has been on a sustainability bent. Its ongoing projects, from Copenhagen’s Fælledby neighbourhood to the World of Volvo experience centre in Gothenburg and Toronto’s highly anticipated development, all balance statement-making design with minimal environmental impact. The firm’s latest undertaking, completed in 2022, is being billed as its most ambitious to date. And yet, unlike the aforementioned projects, it one is of a much humbler scale: a 250-square-metre extension for the Feldballe School in the rural Danish town of Rønde.
The school is a critical hub within the , where residents with low-impact lifestyles have built experimental houses using natural and recycled materials. With its gabled roof, wood façade, and modest size, the new addition fits seamlessly into its bucolic residential context.
In partnership with Danish philanthropic organization Realdania, the firm embarked on a mission to design a building that captures more carbon than it emits: a carbon-storing building. Henning Larsen achieved this goal through an “uncompromising material strategy” that leverages locally sourced, natural and bio-based building materials — namely wood, seagrass and straw — as stand-ins for carbon-intensive concrete, bricks and steel. Though bio-based materials have been used in construction for centuries, they have been adapted to meet modern requirements. In addition to their carbon sequestering properties, these materials are fire-safe, chemical-free and contribute to a comfortable indoor climate through efficient insulation.
The firm worked with Slovakian company EcoCocon to incorporate their groundbreaking panels of compressed straw in wooden cassettes as a primary design element. When used in construction, straw — an increasingly popular renewable resource and a by-product of agricultural practices — is an optimal scalable solution for carbon sequestering and waste management and an alternative to producing new materials. The construction system is adaptable and modular, making it suitable for all manner of building typologies. As a result, the structure embodies a circular ethos; it can be easily disassembled for repair or reuse, making it fully recyclable.
“Thinking critically about the production line in its entirety, we have shown that quality and function are not compromised by using fewer resources,” explains Jakob Strømann, Director of Sustainability and Innovation at Henning Larsen. “For this project, the straw was sourced from as nearby as neighbouring fields.”
The straw panels, which allow humidity to escape, are covered in clay to release and absorb moisture as needed. Natural ventilation, meanwhile, is facilitated by a system made of eelgrass, a common seaweed found along the shores of the Northern Hemisphere. Not only does this eliminate operational energy consumption, but it also allows the classrooms to maintain their full height as there is no need for ventilation ducts or suspended ceilings.
Interior walls and built-in furniture made from untreated plywood imbue the spaces with warmth, while skylights filter in abundant natural light. Above, the roof is made entirely of certified locally produced timber and outfitted with solar panels.
All told, the addition has a footprint of 339 kilograms of CO2e per square metre, encompassing emissions from embodied carbon in materials, technical installations and building operations, calculated over a 50-year span from production to end-of-life.
As its student body reflects a generation that will face the greatest impacts of climate change, it is only apt that the building, which will host science classes, serves as an example of climate leadership. The project has also been a vital learning experience for Henning Larsen, which has since devised an ambitious, forward-thinking framework for sustainable design that considers the entire project life cycle. Its principles include sourcing materials that are local, sustainable, carbon-sequestering, and free of toxins, lowering operational energy through passive design strategies, and designing for disassembly.
And they’re quickly putting the framework into practice. “With Feldballe School as a testing ground for integrating novel solutions, we are already in the process of scaling this model up for a 13,000-square-metre project,” says Strømann.
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