Visit to Groendak part 2: sloped roofs

Back to reporting on our visit to groendak, we also received a lot of information about the options for sloped roofs.

For sloped roofs, groendak offers a standard option up to an angle of 25-30 degrees. The main issue is to prevent materials from sliding off the roof, and there are different techniques for this. Currently there are experiments with Velcro (Belgium) and glue (Netherlands) as alternative materials to prevent slippage. The standard sloped green roof has the same materials as a flat green roof, with these exceptions.

• Soil and substrate - Lava rocks with extra ground layer to prevent sliding
• Filtration layer - special filter with tubes integrated in the fleece (made in Belgium)
• Drainage layer - Rubber plastic EDPM (made in the Netherlands)

 

For higher degree slopes up to 65 degrees, different material is used.

•     Vegetation/substrate mat - Sedum, this can grow up to a slope of 65 degrees. The plant mat is attached to the plastic grid below by thin sticks.
•     Filtration layer - Filtration fleece, water can pass but particles are caught (Belgium)
•     Drainage layer - plastic crate HDPE with metal hooks to prevent sliding, placed every 1.5m
•     Protective layer - Fleece (Belgium)
•     Roof

There is also a groendakpan - a green roof tile. This replaces the standard roof tiles and has a small space for plants to grow in and water to be retained. The normal elements of the roof are beneath the groendakpan, no additional materials are required. The water is drained into the next tile below and then in the roof gutter. Fleece is used inside the tile to pull the water up in the pan. The height of the pan is low compared to a sloped green roof. 

To prevent drought on a sloped roof, an irrigation system with tubes and holes to feed the top of sloped green roofs is developed.

As for performance measurements, flat roof performance has been tested when it comes to temperatures, water retention, and soil moisture content, as compared to a normal roof. For sloped roofs, the performance of the groendakpan has been tested in three locations. None of the green roof types have been subjected to a Life Cycle Assessment. This leaves room for many improvements in the production process.