I have a combustible attic framed with standard wood truss framing. There are dormers that are framed on top of the roof sheathing, that have small 2-ft x 2-ft openings in the sheathing to access the dormer and provide ventilation for the dormers. Both the attic and the dormers are fully protected by the dry system.
My hydraulic calculation area is 2,535 sqft, which is increased for slope and for it being dry.
A dormer falls within my remote area.
My understanding is that the dormer is considered a combustible concealed space per NFPA 13-2019. The small opening of 2-ft x 2-ft is allowed under NFPA 13 Section 3.3.195. Therefore, the dormer space should not be included in the hydraulic calculations, under NFPA 13-2019 Section 18.104.22.168.5.
I am being instructed by an engineer that this area is not qualifying as a concealed space and the additional sprinklers in the dormer need to be included in the hydraulic calculations. Adding the additional 8 sprinkler for the dormer to the already-calculated 34 sprinklers in the attic is causing the possibility of now needing a fire pump.
Am I wrong here?
Do the dormers need to be included in the remote area for this hydraulic calculation?
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