sprinklernotes
Location of Residential Sprinklers with Beamed Ceilings—NFPA 13D
“In a room 25 ft x 25 ft and a flat ceiling with beams that are 8 in., 10 in., and 12 in. deep, can the sprinklers be placed on the bottom of the beam? The beam pockets are 4 ft x 4 ft. We are being told that this isn’t allowed by the ceiling pocket rule?” We have reviewed NFPA 13D, 2016 edition that you indicated as the applicable standard. Our informal interpretation is that sprinklers are placed under the beams. It is not an uncommon mistake to attempt to apply the ceiling pocket restrictions to beamed construction or to wood joist construction for that matter. This is understandable since the space between the structural members is literally a pocket. What they need to understand is that beam and joist assemblies are separately addressed as obstructed construction and ceiling pockets is an indentation in a smooth ceiling. This is better understood by those applying NFPA 13 where there is explicit criteria for obstructed construction. NFPA 13D, though, was historically applied to just smooth ceilings. Not long ago, if it was sloped, beamed, or pitched, NFPA 13D suggested increasing the density and/or increasing the number of sprinklers to be calculated. Then a residential sprinkler was listed for beamed ceilings but the only criterion in NFPA 13D was that the sprinkler must be listed for the ceiling configuration. The installation and design guidance for ceilings with beams was left up to the listing criteria and defined by the manufacturer’s data sheets. A significant change occurred with the 2013 edition when guidance on multiple configurations on beamed construction was added. In particular, paragraph 10.2.1(2) says: “A flat, horizontal beamed ceiling, with a maximum ceiling height of 24 ft (7.3 m), with beams up to 14 in. (355 mm) deep with pendent sprinklers under the beams. The compartment containing the beamed ceiling shall be a maximum of 600 sq. ft. (55 m squared) in area. The highest sprinkler in the compartment shall be above all openings from the compartment into any communicating spaces.” Just like in NFPA 13, we now have obstructed construction with its own criteria. The ceiling pocket criterion still exists but it applies just to what would otherwise be considered smooth construction. Also, just like in NFPA 13, this is not stated but assumed to be understood. The criterion is the same in the 2016 edition. As such, the ceiling pocket restrictions do not apply to beamed construction. As for the placement of the sprinkler in relation to beams, it’s explicitly identified as being under the beam. As learned from the research project completed in 2010 (identified in NFPA 13D: 10.2), it’s interesting to note that the activation time of the sprinklers is adversely affected when they are located at the ceiling in small pockets.
