It is the task of the designer to make adjustments in the green roof system accordingly e g.
Low pitch green roof.
Above 5 degrees roofs are considered to have a pitch which may affect the design.
Sloped roofs retain less water in general and the moisture content varies from the ridge to the eave lowest edge of the roof.
For a green roof installation that pitch should be at least inch per foot of run.
Before the plants go up a structural engineer should check to ensure that the roof can support the weight of the engineered growing medium and plants.
The most crucial component of any sloped green roof is the confinement system which holds the growth medium in place during the roof s early stages of development.
Most vegetation will grow on quite sever slopes but the designer must consider the practicalities of installing the green roof and just as importantly how the roof is to be maintained.
Moreover low slope metal roofs are not prone to the degradation experienced by organic materials enabling these roofs to better resist the elements.
Drainage thickness of growing media plant varieties etc.
Green roofs lower surface temperatures often by 50 degrees fahrenheit or more.
Even a flat roof should have some pitch so that it sheds water toward gutters.