Behind the thick wooden walls of a small school in northern Denmark are two wholly uncommon materials: One is often burned to run the country’s district heating systems. The other usually rots away on the beach.

But at the Feldballe School in Rønde, Denmark, Henning Larsen Architects used these two materials—straw and a seaweed called eelgrass—to form the insulation and ventilation systems of a revolutionary kind of building. Designed specifically to reduce the amount of carbon emissions that result from the building’s construction and operable lifespan, the school is showing how biomaterials can help the construction industry hit environmental targets without sacrificing aesthetics.

The building is a 2,700-square-foot addition to a school that houses classrooms and science labs. With a wood roof and exterior and its straw walls covered with clay-based plaster, the building is a modern interpretation of a vernacular architecture made from the materials available in the environment. Passively heated and ventilated, its projected annual CO2 emissions will be about half of the level allowed under Denmark’s building code.

Jakob Strømann is director of sustainability and innovation at Henning Larsen, and he says the idea for using straw came from a PhD student currently working with the Copenhagen-based firm and researching decarbonization. Strømann says building material choices are becoming increasingly important when it comes to reducing the carbon impacts of construction. In Europe, he notes, the electricity grid is becoming greener, so there are fewer carbon reductions to achieve through energy efficiency. Cutting the so-called embodied carbon, or the emissions that come from producing, transporting, and using materials in the construction process, is the new priority. “There’s a shift in balance now,” he says.

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