3. Special cases of green roofs

3.1 Pitched roofs

• Vegetated roofs are most often built on a terrace with a slope of 1 to 2%, to reduce the thickness of the drainage layer and therefore the overall weight of the structure, and to avoid water stagnation harmful to vegetation. However, sloped green roofs are also available with a maximum slope of 20%. A sloped green roof is technically more complex to install, and the specification must be carefully studied, taking all constraints into account.

  To ensure the durability of a sloped green roof, a distinction must be made between areas with a slope greater than or equal to 3% (zone A), and areas with a central valley or edge (zone B or C) (figure