Steeply sloping roofs are those with slopes greater than 20%. The installation of vegetation systems on steeply sloping roofs differs from that on flat or low-slope roofs (slope less than 20%). Indeed, planting on steeply sloping roofs involves specific constraints: risks of substrate and vegetation erosion, rainwater runoff, overloading generated by the roof. A technical study of the steep-slope vegetation project (overload, structure, roof slope, orientation, length of slope, etc.) is essential to limit these risks and to recommend the most suitable retaining device and watering system.
Prevent plant erosion
In the case of a steeply sloping green roof, the risk of erosion is accentuated during the planting phase (before the plants take root in the substrate).
For this reason, vegetation planting by sowing fragments or planting micro clumps is not recommended for this type of project. Pre-vegetated nursery solutions are more suitable for immediate aesthetic results.
Le Prieuré offers several steep slope planting solutions: ACROPACK® (with HYDROPACK® system), ACROMAT® (with tapid LP Mat) and ACROMOTTE® (for slope planting).
Protect substrate layer from erosion
To prevent erosion or slippage of the substrate down the slope (especially during heavy rainstorms), an anti-slip substrate retention system should be installed on roofs with slopes greater than 20%.
Le Prieuré has developed various retaining systems for steeply sloping green roofs. ACROPACK® systems are compatible with the HYDROPACK® all-in-one tray, and MULTIFIX retaining systems are suitable for LP Mat pre-cultivated mats and planting.
Le Prieuré has developed innovative, technical anti-slip systems (for substrate and vegetation complex); ACROPACK® and MULTIFIX have been validated by a Bureau de Contrôle and are covered by a Cahier des charges de Prescription de Pose for steeply sloping roofs from 20 to 200%.
Reduce stormwater runoff
In the vast majority of situations, the water reserves of the vegetation complex are greatly reduced by the slope. For this reason, automatic watering is strongly recommended.
Le Prieuré has developed watering solutions adapted to the slope and complex used: the distribution of water will be different for each complex.
Regular maintenance
A steeply sloping green roof requires regular maintenance to ensure the survival of the plant cover: pruning, checking the irrigation system and adding fertilizer. The aesthetic result is only guaranteed if these steps are carried out every year.
Le Prieuré offers a specific maintenance contract for all sloping roof greening projects.
Choosing the right green roof complex for a sloping green roof
For green roofs with very steep slopes (up to 200%): the ACROPACK® solution.
Thanks to its walls, which separate the substrate and vegetation, the HYDROPACK® prevents erosion. As steep roofs are often difficult to access, the “all-in-one” format of the ACROPACK® solution facilitates installation. As the trays are pre-cultivated in a nursery for 8 months, rooting the plants through the entire thickness of the complex eliminates the risk of substrate erosion during installation. ACROPACK® can also be used to green roofs with very steep slopes (over 100%).
For atypical steep-slope roofs: the LP MAT multi-layer system with pre-cultivated matting
The ACROMAT® vegetation system with LP MAT sedum matting can be easily adapted to the most atypical projects: rounded shapes, variable slopes (waves), wider range of plants. By increasing the thickness of the substrate layer, it is possible to broaden the plant palette and reduce watering requirements (the substrate is capable of retaining 30 to 50% of its volume in water. This additional reserve optimizes water resources by spacing out watering periods).
