In urban areas pitched Green Roofs are a special attraction. Upwards of 10° shear forces increase with the roof slope and the substrate layer must be protected against erosion. Green roof systems for pitched roofs differ significantly from system build-ups for flat roofs. Plant selection and planting methods are to be adjusted to the relevant slope and exposure.
Root resistant waterproofing is necessary for pitched Green Roofs; installing an additional root barrier, requires much effort and increases the risk of slippage. Stable abutments have to be installed on the eaves edges to transfer shear forces from the Green Roof system build-up and the additional snow load into the roof construction. Additional shear barriers may be necessary to transfer the shear forces depending on the roof slope and the roof length. It is recommended the design for the shear barriers and the eaves profiles be done by a structural engineer.
With increasing slope the Green Roof system build-up is more complicated and the substrate has to be protected from erosion; plastic grid elements can be used for this purpose. Even though it is possible to build pitched Green Roofs with a slope of 45° it is not recommended to exceed 30° due to significant limited accessibility for upkeep and maintenance.
The success of the landscaping on pitched roofs depends on the plants. Appropriate selection of plants is important. Fast surface coverage is the highest priority. A dense planting of root ball plants or pre-cultivated vegetation mats are used in cases of steep slopes and allow for rapid coverage. It is also important to consider the exposure of the roof area, the slope and the location of the building when selecting plants. Perennials and grasses can be used for pitched Green Roofs; whereas, Sedum is the most suitable for pitched roofs, due to the species' high water retention capacity and erosion protection. The water run-off is much faster on pitched roofs compared to flat roof. It is advisable to plan for an additional irrigation system to provide water during dry periods. The irrigation can be provided either by drip irrigation or by sprinkler systems.