gulkhan123
Member
Q: What is the depth above ceiling(ceiling void) that requires smoke detectors as per NFPA72?
No specified depth. If there are comustibles, you need them. That begins with the guess that the Building Code sent you to NFPA 72 to determine installation requirements.
The requirement for coverage areas are found in the adopted building code.
If it was up to 72 only, they would want it everywhere, but you don't need that in most installations.