Retention Roof – A Definition
The term “retention” derives from the Latin word “retinere”, meaning “to hold back”. In water management, it describes the balancing effect of retention spaces on water runoff into existing watercourses such as streams and rivers. In practical terms, an additional layer – known as the retention space – is incorporated between the upper green roof build-up and the roof waterproofing membrane. This layer can absorb water, store it for a defined period of time, and then release it in a controlled manner into the drainage system via a throttle outlet. The retention space typically consists of plastic elements.
Retention Roofs Are Commonly Used in Particular For:
- extensive green roofs
- intensive green roofs
- pedestrian and vehicle surface coverings, for example on underground car parks
Retention Roofs Are Becoming an Increasingly Popular Climate Adaptation Measure
Dr Gunter Mann, President and Managing Director of the German Federal Association for Building Greening (Bundesverband GebäudeGrün, BuGG) – link to website (in German) – is pleased to see that many planners, as well as representatives of local authorities, have recognised that retention roofs can relieve drainage systems during heavy rainfall and reduce the risk of flooding and water damage. He says: “Where green roofs – ideally in combination with retention spaces – are legally embedded in development plans, this has positive effects on the local climate. Green roofs are additional green spaces with all the associated benefits, including increased evapotranspiration and the resulting cooling effect. This is particularly advantageous in inner-city areas.”
Funding Opportunities for Retention Roofs and Green Roofs
Landscape gardeners and contractors with an interest in green roofs in general, and retention roofs in particular, can find useful background information from the European Federation of Green Roof and Living Wall Associations (EFB), the umbrella organisation of national green roof associations across Europe, including BuGG in Germany. Funding schemes for green roofs vary by country, region and municipality, so it is worth checking directly with local authorities or planning offices to find out what support is available in your own area.
A particularly practical resource is the Stormwater Management Roof planning guide published by manufacturer Zinco, available as a free PDF download in English on the company's website. You can find Zinco at GaLaBau in September 2026 in Hall 3A at Stand 3A-131. Further established green roof companies can be found via the exhibitor search linked here.
