Research roof garden substrates nearly ready

31 october 2016

Last year, RHP started a research concerning roof garden substrates. In the coming period, samples will be taken for the last couple of times and all physical analyses can be compared. How has the research passed off so far?

The aim of the research is to answer the question: what is the bulk density and water- and air balance of the roof garden substrates compared to the laboratory method according to the guidelines for roof vegetation of the German FLL (Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau)? In order to answer this question, RHP set up a practical set up with six different roof garden substrates of certified companies with the RAG Greenroof quality mark. The effect of vegetation and blowing on the roof is examined too.


The effect of the precipitation quantity on the water content, so the water storage of the roof garden substrate, can be clearly determined from the water content measurements. Water storage is one of the most important advantages of a covered roof. Meanwhile most samples have been taken from the cases and the last few measurements are currently being processed and all physical analyses can be compared in the coming period. This winter the individual results will be discussed with the certified companies concerned.

Requirements and guideline

A product certificate belongs to RAG Greenroof in which requirements are drawn up concerning the physical aspects of roof garden substrates. These have been copied directly from the German FLL guideline. However, it is insufficiently known whether these values also provide the desired information to guarantee a good plants growth for the Dutch substrates. Our research has to show this. Anyway the FLL guideline will shortly be incorporated in the NTA (Nederlandse Technische Afspraak) for covered roofs.

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