Guidelines for the Planning, Construction and Maintenance of Green Roofing (2018 Edition)
About this book
The FLL Guidelines for the Planning, Construction and Maintenance of Green Roofing, published by the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL) — the German Landscape Research, Development and Construction Society — are the internationally authoritative technical standards for green roof design, construction, and maintenance. First published in German in 1982 and regularly updated, the guidelines are the primary reference for green roof technology worldwide, translated into English and referenced in building standards and green roof guidelines across Europe, North America, Asia, and beyond. The FLL guidelines distinguish between the two fundamental types of green roofs: extensive green roofs, which have shallow growing media (typically 60-200 mm deep), low-maintenance drought-tolerant planting (typically sedums, mosses, and herbs), and are designed primarily for environmental performance functions including stormwater management, thermal insulation enhancement, and urban heat island mitigation; and intensive green roofs (roof gardens), which have deeper substrate layers (200 mm to over 1,000 mm), support a wider variety of plants including shrubs and trees, and require regular maintenance.
Both types are covered in the guidelines with appropriate technical requirements for each. The technical structure of the guidelines addresses each layer of the green roof assembly: the waterproofing membrane and root protection layer; the drainage layer (which manages excess water and prevents waterlogging while retaining moisture); the filter layer (which prevents fine particles from migrating into the drainage layer); the growing medium (substrate); and the vegetation. Detailed requirements are given for each layer's performance characteristics, thickness ranges, and testing procedures, with specific attention to the German FLL test methods for growing media (FLL substrate testing protocol) and the drainage rate of drainage layers.
The guidelines provide detailed design requirements for structural loads — distinguishing between dry, saturated, and wet (maximum water-bearing) states for each substrate type — which is critical information for structural engineers assessing the bearing capacity of the supporting structure. Fire performance requirements and the design of sedum/wildflower "seed mixes" for extensive roofs are also addressed. Sources: FLL (fll.de); FLL Green Roofing Guidelines 2018 Edition official publication; Green Roof Technology references; ASTM E2399 and EN standards.