Paved areas suitable for greening

The new FLL guidelines

In July 2018, the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e. V. (Research Society for Landscape Development and Landscape Construction; FLL) published a fundamentally revised edition of the “Richtlinien für Planung, Bau und Instandhaltung von begrünbaren Flächenbefestigungen” (Guidelines for the Design, Construction and Maintenance of Paved Areas Suitable for Greening). A clear distinction is now made between “pavers with grass joints”, “grass pavers”, and other types of construction. Four illustrations show the layer structures for different loading situations. The first three of these so-called categories of use (N 1 to N 3) were adopted from ZTV-Wegebau (Zusätzliche Technische Vertragsbedingungen für den Bau von Wegen und Plätzen außerhalb von Flächen des Straßenverkehrs; Supplementary Technical Conditions of Contract for the Construction of Paths and Public Spaces outside Areas of Road Traffic; FLL 2013). The N Fw category of use was added in order to account for the special requirements placed on areas for fire engines on plots of land.

As regards the properties of paving blocks, paving flags and grass pavers, reference is made to TL Pflaster-StB (Technische Lieferbe-dingungen für Bauprodukte zur Herstellung von Pflasterdecken, Plattenbelägen und Einfassungen; Technical Delivery Conditions for Building Products for Installing Paving Block Surfaces, Flag Pavements and Edgings), and to the guideline “Nicht genormte Betonprodukte” (Non-Standardized Concrete Products; BGB-RiNGB) published by Bund Güteschutz (Quality Assurance Association for Precast Concrete and Reinforced Concrete Elements). In addition, the products must be suitable for the intended loading / category of use. For the bedding and filling substrate, the ruleset requires, among other things: content of organic matter between 1 and 3% by mass, water permeability at least 1 x 10-5 m/s, water-holding capacity between 20 and 40% by volume, as well as limit values for air-holding capacity, salinity and pH value.

There are quality specifications also for the installed pavement suitable for greening. The requirements on evenness specify, for example, a permissible gap dimension below the straight edge of 12 mm with a distance between measuring points of 4 m, of 10 mm with a distance between measuring points of 2 m, and of 8 mm with a distance between contact points of 1 m. These measurements refer to the top side of the pavement materials, since the surface of the joint substrate should be approx. 20 mm below the top edge of the same. In addition, the water infiltration rate must reach at least 18 mm/h, and the deviation from the design level must not exceed 20 mm.

This FLL ruleset is intended to establish itself as accepted technical state-of-the-art. For the time being, the parties involved in construction should agree on its application in order to create reliable standards.

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