Specially developed for retention roofs, the SitaRetention product family ensures that the rainwater is retained for a certain period of time on the roof. With SitaRetention Fix or SitaRetention Twist without dome grate, together with the SitaRetention green roof shaft, any green roof can be upgraded to a retention roof. On flat roofs without ballast, SitaRetention Twist with dome grate efficiently reduces the load on ground pipelines during heavy rainfall events. This guarantees controlled discharge of the rainwater for retention roofs.