Are smoke detectors required above false ceiling knowing that all cables distribution inside the residence is executed on cable trays and the false ceiling is used as plenum for ac return air?
If the adopted building safety regulations require total smoke detection coverage -- yes.
Total smoke detection coverage is typically restricted in extent in today’s building safety codes, as total coverage smoke detection is usually not required in buildings that have sprinkler protection. So consult the local building safety regulations again. There may be a few instances where an occupancy type would require total smoke detection coverage and sprinklers are not required or provided. Total coverage smoke detection may be required when replacing an old fire alarm system in an existing building (health care, ambulatory care, detention and correctional and etc occupancies.) that doesn’t have sprinklers. In that case, the total smoke detection coverage must be maintained.
For instance 2015 NFPA 101 has provisions for total (complete) smoke detection in Sections 126.96.36.199.5.2, 188.8.131.52.2.1, 184.108.40.206.2.3, 220.127.116.11.3.2, 18.104.22.168.5.2, 22.214.171.124.2.1, 126.96.36.199.2.3, 188.8.131.52.3.2, 184.108.40.206.3, and 220.127.116.11.3.
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