Thanks for the welcome, Tim. This is certainly a warm
online community!
Our green roof builder (Leslie Doyle at Restoration Gardens) gives me these general rules of thumb for fully saturated green roof weights:
Extensive (thin growing medium, mostly sedum-based plantings): 10-35 lb/sf
Semi-intensive (soil/growing medium hybrid, flowers and grasses): 35-50 lb/sf
Intensive (soil, flowers, grasses, vegetables & small shrubs): 50-300 lb/sf
These are still pretty wide ranges, but will give you some idea. Of course, you must add the full snow load to these figures in cold climates.
Hope this helps!
