Glossary

Waterproofing
Waterproof membrane for protecting a building against water.

Run-off coefficient
This is the proportion of water that runs off following a period of rain. For roof plantings with a layer thickness of 10 - 15 cm, the run-off coefficient according to FLL is 0.3.

Spray planting
Mechanical planting process whereby sedum sprouts and special seeds combined with mulching materials, fertiliser and other soil-improvement agents are applied in a single operation.

Bitumen
Viscoelastic distillate from crude oil used for producing bitumen membranes and adhesive compounds.

Bitumen membrane
Reinforcement with bitumen facing on both sides.

Roof system
All the layers with different functions that make up the roofing system as a whole.

Drainage layer
For safely removing excess water. Often in the form of a combined water storage and drainage layer capable of water retention.

Root barrier
Layer that prevents roots from growing through the waterproofing membrane. Protection against root penetration can be achieved by the waterproof capping sheet itself or by a separate root-resistant layer.

Single-layer design
A form of extensive planting whereby a special single-layer substrate performs multiple functions as a drainage, filter and vegetation layer.

Development and maintenance care
Extensive plantings should continue to be maintained after the acceptance inspection. Development and maintenance care ensures that the roof planting will perform well in the long term.

Extensive planting
The aim of extensive planting is to achieve natural, lightweight vegetation that requires only minimal maintenance.

Follow-up care
Includes all maintenance performed until the planting is ready for acceptance by the client, as defined in the FLL guidelines for the planting method in question. Extensive plantings are low-maintenance, but not maintenance-free.

Filter layer
Prevents fine particles being washed from the vegetation layer into the drainage layer, thereby ensuring that the drainage layer remains functional.

FLL
Forschungsgesellschaft für Landschaftsentwicklung und Landschaftsbau e. V., Bonn (Landscaping and Landscape Development Research Society) Organisation that issues guidelines on green roofs.

Surface water drainage charge
A growing number of municipalities are offering discounts of up to 50% on surface water drainage charges for buildings with green roofs. This is because green roofs reduce and delay rainwater run-off into the sewerage system.

Green roof system
All the components of a green roof system above the waterproofing membrane.

Intensive planting
Green roof with a thicker substrate and a garden-like design, requiring more maintenance. Can be designed to permit recreational use, and is then barely distinguishable from a ground-level gardena.

Multi-layer structure
Functional division of the green roof into drainage, filter and vegetation layers. This structure is advisable for extensive plantings and obligatory for intensive plantings.

Retention
A green roof has the effect of retaining rainwater. Since water run-off is reduced and also delayed, peaks of run-off flow are capped.

Richtlinien für Dachbegrünungen (Green Roof Guidelines)
Full title: "Richtlinien für die Planung, Ausführ ng und Pflege von Dachbegrünungen" (Guidelines for the Planning, Execution and Upkeep of Green-Roof Sites), issued by FLL (1990/1995). The most important set of rules for roof planting, widely recognised by planners, contractors, clients and experts in the field.

Protective layer
Protects the roof waterproofing membrane from physical damage.

Sedum
Many species of sedum are very drought-resistant and extremely hardy. This is why they are ideal for planting on roofs. For a new planting, sedum sprouts (cut-off plant shoots) can be scattered around the roof.

Substrate
See vegetation layer

Substructure
Underlying structure supporting the roof system.

Vegetation layer
The vegetation layer holds all the plants' root systems, and must provide good growing conditions on the roof. Vegetation substrates for roof planting are real all-rounders. Key factors for the quality of vegetation substrates are their water storage capacity, structural stability, water permeability and particle size distribution.