Soilless cultivation of tomatoes in the greenhouse is a source of waste in form of mineral wool polyethylene. Utilisation of mineral wool waste originating from horticulture is still unresolved and rises a lot of controversy The aim of the study is to evaluate the possibility of using mineral wool waste in the construction of a green roof. To find the answer, physical properties, i.e. water absorption, water capacity and leachability were assessed for fresh mat and mineral wool waste. Preliminary assessment of pollutants leaching from mineral wool waste was also performed. It was found that the physical properties of the used mats are different from those of the input material. The content of phosphorus in leachate from used mineral wool derived from greenhouse cultivation excludes its use as a material for green roofs construction, if the runoff is discharged into water bodies.