Guidelines for the Planning, Construction and Maintenance of Green Roofing — Green Roofing Guideline
About this book
Guidelines for the Planning, Construction and Maintenance of Green Roofing — Green Roofing Guideline, published by the Research Society for Landscape Development and Landscape Design (FLL — Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V.), is the definitive technical standard for green roof design, construction, and maintenance. The FLL guidelines are recognised internationally as the primary reference document for the green roof industry, forming the basis for national standards in Germany and influencing green roof specifications worldwide. The guidelines apply to all categories of green roof construction: extensive green roofs (thin substrate layers of 6–15 cm, low maintenance, primarily sedum/moss vegetation), simple intensive roofs (substrate depths of 15–25 cm, drought-tolerant perennials and grasses), and intensive green roofs (substrate depths exceeding 25 cm, capable of supporting shrubs and small trees, requiring irrigation).
The guidelines also address brown roofs designed for biodiversity value, solar photovoltaic/green roof combinations, and parking deck greening. A central contribution of the FLL guidelines is the definition of the green roof construction assembly and its component layers: the root barrier membrane, drainage layer (mineral aggregate, plastic sheet elements, or recycled rubber products), filter layer (geotextile), growing substrate (mineral-based growing medium meeting FLL substrate specifications), and vegetation layer. Specifications for each component layer are provided in terms of physical properties, long-term stability, and compatibility with other layers.
The structural implications of green roofs are addressed in detail: dead loads from saturated substrate and water retention, dynamic loads from saturated substrate drainage, and wind uplift forces at roof edges and corners. Load calculations and guidance on anchoring systems at roof perimeters are provided for different substrate depths and building height categories. Waterproofing membrane selection and root protection are critical safety requirements: the guidelines specify test procedures for root resistance of waterproofing membranes (FLL root resistance test) to prevent plant roots from penetrating and damaging the building envelope.
Inspection regimes and maintenance schedules are specified for each green roof category, including plant replacement, substrate pH adjustment, weeding, and drainage system inspection.