The research programme "Fifth Dimension - green roofs and wals in urban areas" aims to produce high-level scientific and broadly applicable knowledge on optimal green roof solutions in Finland. Scientifically, green roofs serve as experimental model ecosystems for research and provide an opportunity for inter- and transdisciplinary research that is societally relevant. The research policy of the programme includes working in close contact with the end users of scientific knowledge, such as municipal and state authorities, companies and citizens. Our main target concerns the potential of green roofs to enhance urban nature and ecosystem services, as part of multifunctional urban green infrastructure. The aim of the programme is to evaluate the various benefits green roofs may offer, and to develop optimal solutions and designs for green roofs that offer the best possible services for urban residents.