Feldballe Friskole: Extension in Straw, Eelgrass, and Wood

Feldballe Friskole is an independent school located in Djursland – a peninsula north of Aarhus. With a special extension featuring walls made of straw, a wooden roof, and materials free from chemicals, it’s referred to as a green experiment. The extension aims to demonstrate that architecture can be built from materials that are environmentally friendly.

The main building at Feldballe Friskole has a classic Danish 1955 design—red bricks with white window frames. Consequently, the wood-clad extension stands out. Adding an extra 250 square meters, it provides space for a new wing with a physics and chemistry lab and a classroom for older students. But it also accommodates new methods of construction using different materials than we’re used to. Here, straw, eelgrass, and wood have been utilized, which are more environmentally friendly compared to conventional building materials.

Feldballe’s Five Dogmas

The aim of Feldballe Friskole was to have an extension that could educate students about the green transition and so-called biogenic materials—materials formed by nature itself, typically sequestering carbon during growth. The building was also meant to have a healthy indoor environment, an attractive architectural expression, and a climate-positive footprint. To ensure no compromises were made with the ambitions, the project team established five principles for themselves:

1. Use of renewable, bio-based materials.
2. Reuse of locally produced materials.
3. Utilization of non-toxic materials with minimal off-gassing.
4. Ensuring a healthy indoor environment based on good daylight levels, natural ventilation, and low energy consumption.
5. Design for Disassembly, allowing building components to be reused in other projects in the future.

Constructed with Climate-Positive Blocks

The primary design element comprises compressed straw in wooden cassettes assembled as large blocks. When the building no longer stands, these blocks can be dismantled and reassembled elsewhere in a new design. This phenomenon aligns with dogma 5, known as Design for Disassembly.

The surface of the straw panels is covered in clay and clad with locally produced wood inside and out. They are free from toxic chemicals, fire-resistant, and excellent moisture regulators, effectively insulating the building. Straw is also an eco-friendly choice due to being a rapidly renewable byproduct.

The Foundation is Still Concrete

However, trees don’t grow to the sky — or in this case, into the ground. Partly due to budget constraints, the building stands on a foundation made of concrete. The original plan was for a wooden foundation on screws, but it proved too costly and raised uncertainties in the solution among contractors.

From Small to Large Scale

In the ventilation system, eelgrass has been utilized. Eelgrass is a common type of seaweed found along coastlines in the northern hemisphere. The eelgrass has been pressed into cassettes placed around the windows, serving as a ventilation system that creates a well-functioning indoor climate. All these natural elements give the extension a warm and inviting appearance, and because there’s no need for extensive ventilation systems or suspended ceilings, the spaces are spacious and lofty.

So, despite a few hiccups with concrete, the project has been seen as an informative experiment, with the idea that both materials and concepts from the project can be scaled up for larger endeavors.