NFPA 72 code sections · Installation Guidelines
Smoke detectors go in last — after every other trade has cleaned up
Drywall dust, sawdust and paint overspray ruin smoke detector chambers. The code requires that smoke detectors not be installed until after construction cleanup of all trades is complete and final. If detectors must be installed earlier (for example to protect the building during construction), they are covered or replaced, and detectors contaminated during construction are cleaned or replaced before acceptance. Heads that have been sitting in a dusty ceiling for six months will fail sensitivity tests and generate nuisance alarms on day one.
NFPA 72 reference
Chapter 17 — Initiating Devices
17.7.1.11 smoke detectors installed after construction cleanup of all trades (17.7.1.10 in some editions); 17.7.1.12 protection of detectors installed before cleanup
References use NFPA 72 2019/2022 numbering — section numbers can shift between editions, so confirm in the edition your AHJ has adopted.
On the job
A general contractor insists detectors be installed with the ceiling grid so the inspector 'sees them'. Three months of sanding and sweeping later, 40 percent read above their sensitivity range at acceptance. The alarm contractor eats the cost of cleaning and replacing heads. On the next job the bases go in with the grid and the heads go in the week before the final.
Quick check
1. Smoke detector heads should be installed:
2. A detector that was exposed to construction dust must be:
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