Section 17.5.3/Smoke Detector Spacing (2019 Edition)
NFPA 72 2019 Section 17.5.3 covers spot-type smoke detector spacing including the 30-foot nominal spacing, the edition referenced by IBC 2021.
Spot-type smoke detectors must be spaced based on the 30-foot nominal spacing. On smooth ceilings, detectors must not be more than 30 feet apart and not more than 15 feet from any wall. For corridors 15 feet or less in width, detectors may be spaced up to 41 feet apart (the diagonal of the 30-foot coverage square applied linearly). Ceiling heights above 10 feet may require reduced spacing. Detectors must be mounted on the ceiling or on sidewalls between 4 and 12 inches from the ceiling. Beams deeper than 4 inches create individual coverage zones.
Key differences from NFPA 72 2022
The smoke detector spacing requirements in Section 17.5.3 are essentially unchanged between the 2019 and 2022 editions. The 30-foot nominal spacing, corridor extension to 41 feet, and ceiling height adjustments are the same. Minor editorial changes were made in 2022 but the technical requirements are identical. IBC 2021 references the 2019 edition; IBC 2024 references the 2022 edition.
What plan reviewers look for
Plan reviewers check the reflected ceiling plan for smoke detector locations and measure the spacing between adjacent detectors. They verify no point on the ceiling is more than 21.2 feet (the diagonal of a 15-by-15-foot square) from a detector. In corridors, they verify the 41-foot maximum spacing applies only when the corridor is 15 feet or less wide. They check for detectors at the top of stairways and in elevator lobbies.