What are the requirements for spacing of smoke detectors installed on ceilings with beam pockets?
The picture below is smoke detectors within beam pockets in a building being renovated. The ceiling height is roughly about 25 feet and the beam depth is roughly 3 feet. NFPA 72 17.7.3.2.4.2 give us the guidelines for installing smoke detectors in level ceilings with beam pockets.
17.7.3.2.4.2 For level ceilings, the following shall apply:
(1) For ceilings with beam depths of less than 10 percent of the ceiling height (0.1 H), smooth ceiling spacing shall be permitted. Spot-type smoke detectors shall be permitted to be located on ceilings or on the bottom of beams.(2) For ceilings with beam depths equal to or greater than 10 percent of the ceiling height (0.1 H), the following shall apply:
(a) Where beam spacing is equal to or greater than 40 percent of the ceiling height (0.4 H) spot-type detectors shall be located on the ceiling in each beam pocket.
(b) Where beam spacing is less than 40 percent of the ceiling height (0.4 H), t.he following shall be permitted for spot. detectors:
i. Smooth ceiling spacing in the direction parallel to the beams and at one-half smooth ceiling spacing in the direction perpendicular to the beams
ii. Location of detectors either on the ceiling or on the bottom of the beams(3)*For beam pockets formed by intersecting beams, including waffle or pan-type ceilings, the following shall apply:
(a) For beam depths less than 10 percent of the ceiling height (0.1 H), spacing shall be in accordance with 17.7.3.2.4.2(1) .
(b) For beam depths greater than or equal to 10 percent of the ceiling height (0.1 H), spacing shall be in accordance with 17.7.3.2.4.2(2).
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