We use demolition waste and sewage sludge in the substrate for green roofs

In Karviná, a sustainable green roof was installed with RECIHLI substrate, developed by the research team of Urban Ecohydrology of the CTU UCEEB in cooperation with AdMaS CTU Brno and Sedum Top Solution s.r.o. The aim is to evaluate in detail the properties of the substrate, whose formula using recycled construction waste and sewage sludge protects the utility model. Once certified, RECIHLI will be offered commercially as a circular solution for extensive green roofs.

The use of construction demolition waste in substrates for green roofs has not yet been fully explored. The aim of our research is to evaluate in detail the effectiveness of the proposed RECIHLI substrate and to monitor the development of the vegetation surface. In addition, we will monitor the stable carbon content of biochar, which decomposes very slowly in the soil and should not be released to the atmosphere. We are currently working with BBCom, the company involved in the production of the substrate, to get the substrate certified so that we can offer RECIHLI as a commercial solution for extensive green roofs.

The green roof in Karviná was implemented within the Horizon ARV project - Climate positive circular communities. It is a thin, extensive green roof that contributes to the principles of the circular economy by using recycled materials. Its design was co-authored by Ing. arch. Libor Kovář and the implementation was carried out by Green Depot. 

In view of the limited load-bearing capacity of the existing roof, a thin, extensive construction with a hydro-accumulation layer made of Aquadesk panels from Retex, manufactured from recycled polyester fibres bonded together with fusible fibres, was chosen. The RECIHLI experimental substrate contains, in addition to the usual raw materials, admixtures of 9% recycled brick rubble and 10% biochar (kalochar) produced by pyrolysis of sewage sludge. This sludge is produced during wastewater treatment and opens up the prospect of using sewage sludge as a future source of material. For 1 m2 of roof in Karviná with a substrate thickness of 3 cm, we used 3 kg of construction recyclate and 2 kg of biochar.