I recently looked at a commercial flat roof on a restaurant that was completely rotted out. It’s 1000 sq feet (20x50) and the roof deck is 18 feet from ground level.
All of the OSB was gone. Nothing but saw dust left. The only thing left was a layer of TPO, a layer of EPDM, and a layer of soggy fiber board. No one should have been walking up there.
The rafters all have significant rot in the first inch and a half across the tops as well.
They want to do a complete tear off and the following…
1 - Replace or sister all damaged rafters that span 20 feet (16 OC 2x12).
2 - Build a raised low slope frame from front to back across the entire 50 feet.
3 - Add all new 3/4 CDX.
4 - Add 1" ISO board on top of the CDX.
5 - ADD 60 millimeter EPDM to top it off.
There’s also 2 large AC units and a walk in cooler compressor that will need to be craned off the roof. They would also like to remove a two old hood vents and a non working compressor that are no longer in use.
The walls around the perimeter are 2 feet tall and 140 total linear feet. I’m in the Chicago suburbs.