As a general rule, flat roofs should be laid to fall of at least 2°. This is particularly important when designing an extensive Green Roof with a shallow drainage and substrate layer as any deflection in the deck allowing water to pond above the drainage layer will be harmful to the plants.
However, Green Roofs can be installed on zero degree roofs where deeper puddles remain, provided that the correct build-up is designed to avoid the danger of drowning the plants. The standard System Build-ups for extensive Green Roofs are to be adapted to these requirements. By using Floraset®, a deeper drainage element (50 or 75 mm), the necessary distance between the water level and the vegetation layer is ensured. The System Build-up is higher, but not heavier compared to a standard build-up. The Floraset® elements are made of expanded polystyrene thus they are light-weight.