Green roofs are not only green oases in the city, but also serve a variety of other functions and have diverse effects on their surroundings. They can create additional green spaces and open areas in limited spaces, provide areas for species-rich habitats, and reduce the physical, chemical, and biological stress on the roof—to name just a few benefits ¹.

It is particularly important to use high-quality materials properly to ensure a durable waterproofing system. For this reason, membranes and coatings used in this application must meet specific requirements for root resistance. Since past experience has shown that mechanical tests on membranes and coatings are insufficient to assess root resistance, a “Method for Testing the Root Penetration Resistance of Root-Barrier Membranes” was developed as early as 1984 ¹.

Today, the root resistance of membranes and coatings used in green roofs is tested in accordance with the updated Green Roof Guidelines of the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e. V. (FLL) or DIN EN 13948. In these tests, the relevant waterproofing membranes or coatings are professionally installed in planting troughs. These are planted with the ornamental shrub firethorn (Pyracantha coccinea) and the native grass couch grass (Agropyron repens) for the 2-year test. During interim assessments and at the end of the test period, root and rhizome penetration is evaluated, and the certificates “root-resistant” or “rhizome-resistant against couch grass” are issued upon successful completion of the test ^1,2.

In accordance with DIN EN 13948 for determining root resistance, the planting troughs are planted exclusively with firethorn. Thus, passing a test in accordance with the green roof guideline also implies passing DIN EN 13948 ^1,3.

The SKZ is currently the only testing laboratory capable of determining the rhizome resistance of waterproofing membranes. Here, using common reed (Pragmites australis) and a customized installation in the planting troughs, a real-world installation scenario is simulated in which approximately 2 m² of waterproofing membrane with a 5 m seam length can be tested per trough. The rhizome resistance of such membranes exceeds that of roof waterproofing membranes, as reed plants can exert significantly stronger rhizome growth on water-retaining membranes ^2,4.

On August 1, 2017, the SKZ put a greenhouse into operation. This allows for year-round testing of plastic products using various test plants. In conjunction with its accreditation by the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL), the SKZ now offers testing of the “root resistance of membranes and coatings for green roofs” in accordance with FLL guidelines or DIN EN 13948.

In addition to the tests described here, the SKZ conducts further root resistance tests. For example, in the field of geosynthetic membrane systems, the lupine test is performed in accordance with DIN CEN/TS 14416 ⁵.

Furthermore, in accordance with FLL guidelines, waterproofing systems can also be tested using other test plants with even more vigorous rhizome growth. These include, for example, bamboo species often used for landscaping purposes, such as Phyllostachys aureosulcata f. aureocaulis ⁶.

Finally, the expertise developed in the field of root resistance will be used to test other products as well. These include, for example, seals for wastewater pipes and sewers to prevent root ingrowth.

In this project, we are testing:

• “Method for Testing the Root Resistance of Membranes and Coatings for Green Roofs” in accordance with the Green Roof Guidelines of the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e. V. (FLL), Appendix C
   
• DIN EN 13948 “Waterproofing membranes—Bitumen, plastic, and elastomer membranes for roof waterproofing—Determination of resistance to root penetration”
   
• Testing according to individual requirements, e.g., testing of components, pipe systems, or similar items.