Knowledge Voucher: Edible green roofs using sheep wool - Circular Urban Farming

9 September 2025

Green roofs cool cities, support biodiversity, and benefit the environment. But what if green roofs could also become a place for food production, right on top of the building, using residual streams that would otherwise go to waste?

Eduard Beekhuizen, entrepreneur and founder of Rivus Domus, had been frustrated for years by “sustainable” solutions that turned out not to be all that sustainable. In his world of roofing, including sedum roofs, he saw rooftops full of plastic, imported materials, and green projects that felt more cosmetic than meaningful. Until he asked himself: can we do this differently?

From residual stream to growing medium

Part of his answer came from an overlooked resource: sheep wool. In the Netherlands, around 1.5 million kilograms of sheep wool end up as waste every year. Yet wool contains natural nutrients (such as nitrogen, potassium, and sulfur), retains moisture, suppresses weeds, and is biodegradable. That makes it a sustainable alternative to peat or rockwool.

Together with students and researchers, the idea emerged to use sheep wool as a growing medium for cultivating herbs on rooftops. That led to a pilot project: edible green roofs, with herbs harvested directly for the company restaurant located under that same roof.

Student research with real impact

With support from a knowledge voucher from Flevo Campus, in collaboration with Horizon Flevoland, a partnership began with students from Aeres University of Applied Sciences and researchers from the Circular Farmyards research group. In a test environment, they explored:

• Which herbs and crops are suitable for cultivation in a wool-based growing medium

• Whether plants grow better from seed or from cuttings

• The impact of different irrigation approaches

Research setup and results

To answer these questions, the students set up three test beds. Each bed received a different watering strategy, ranging from rainwater only to scheduled irrigation twice a week. The beds included herbs such as mint, thyme, oregano, and chamomile, grown partly from seed and partly from cuttings. Less common varieties such as summer savory, wild marjoram, and winter purslane were also tested.

The test beds were set up as follows:

• Bed 1: fully dependent on rainwater

• Bed 2: watered only when clear drought signals appeared, such as drooping leaves or cracking soil

• Bed 3: watered on a fixed schedule (twice per week)

This setup produced a surprising number of insights, not only about irrigation, but also about cultivation methods and the properties of the wool-based medium itself. The results were telling:

• Cuttings performed better than seeds

• Chamomile was the most successful seed-grown plant

• Bed 2 (adaptive watering) produced the best plant development

• The growing medium used was not ideal: too much wool, too little nutrition

• Compost or adjusted ratios are needed

From pilot to scalable solution

What started as a pilot is now developing into a scalable project and business case. Beekhuizen is currently working with the Central Government Real Estate Agency (Rijksvastgoedbedrijf) on follow-up research at a larger scale. They are also testing how a kitchen can be directly connected to rooftop yield.

The goal: no distribution, no transport, but a short, circular chain - from roof to plate. In the future, this system could create opportunities for growers and green-roof specialists who want to focus on rooftop farming, and for companies that want more from their roofs than just greenery. Roof to plate is a real opportunity for more circular, local food production in the city.

Real sustainability is local, edible, and circular

This project is a pure example of a short supply chain. It shows that real innovation is not always about expensive technology, but about smart combinations of what already exists: local residual streams, natural materials, knowledge, and a strong idea. It’s also a clear example of multifunctional space use, combining food production, biodiversity, and biobased building in one.

Want to learn more?

Curious about the full research? Download the report or contact the entrepreneur at info@rivusdomus.nl.