Hi everyone!

I have a very specific question regarding vegetated area. Should the earth depth under the vegetated area be of a minimum thickness in order to be considered as vegetated area?
The project we are working on is located in a very dense area (thus earning SS credit 2), so that the whole area is built on a big concrete slab; vegetated areas are thus also built on concrete, and not directly linked to the natural ground. Should I look to the local definition of vegetated area? What are the restrictions for LEED, I did not find anything about it?

Thanks!