Towards A Fully Biobased Green Roof: Lessons From The Roofed Green Tray

Green roofs are widely used in architecture. They help manage rainwater, support biodiversity and improve thermal performance. Yet many systems still rely heavily on synthetic materials. In fact, conventional green roofs can contain up to 50–75% plastic. Architect Jennifer de Jonge, founder of Faunest, aims to change this. She is developing a fully biobased and self-sustaining green roof system: the Roofed Green Tray.

Rethinking Materials: The Potential Of Wool

A key material in this project is locally sourced sheep’s wool. Only a small share of Dutch wool is suitable for textiles. The rest often ends up as waste. De Jonge sees this as a missed opportunity.

Most green roofs use mineral wool as a base layer for water retention. However, this material requires a lot of energy to produce and is difficult to recycle. It also supports little soil life. Wool offers a natural alternative with strong performance.

Wool absorbs water both within and between its fibres. It works like a sponge, storing moisture and releasing it slowly during dry periods. It also insulates and keeps plant roots cooler. This reduces stress during temperature changes. These properties make wool an attractive option for circular and nature-inclusive design.

Testing A Biobased System

The team tested the Roofed Green Tray for 2.5 years at The Green Village. They worked together with Babylondaken and Circuwall. The system uses modular wooden crates made from residual timber. Layers of willow branches and sheep’s wool sit on top. Each material breaks down at its own pace, supporting a fully biobased lifecycle.

The modules are lightweight and easy to install. At the same time, they stay stable in place. Water flows through and under the crates, which prevents stagnation and reduces the risk of wood decay.

Key Findings And Challenges

During testing, the wool layer supported a rich soil ecosystem. This is rarely seen with mineral-based materials. However, the wool decomposed faster than expected. As a result, plants did not have enough time to develop strong root systems.

The team identified two main improvements. First, the system needs an extra layer between the wood and the wool. This will slow down decomposition and improve stability. Second, a more diverse mix of plants could strengthen the system. Different root structures and growth rates can improve resilience and support biodiversity.

Towards Scalable Biobased Roof Systems

The Roofed Green Tray is still under development, but it shows strong potential. It offers a circular alternative to conventional green roofs. The project highlights the need for material innovation based on real performance data, such as insulation and water retention.

De Jonge is looking for partners to continue developing the system. She aims to work with green roof specialists and other experts. Further research and investment will help bring this biobased solution into mainstream architecture.

Source & photos: The Green Village