Determining the Percent Reduction in Design Area - NFPA 13

[MedullaOblongata]

NFPA 13 11.2.3.2.3.3 “Where quick response sprinklers are used on a sloped ceiling or roof, the maximum ceiling or roof height shall be used for determining the percent reduction in design area.”

Its a light hazard occupancy building and has sloped ceilings, the maximum ceiling height is 19’-0”. NFPA 13 requires 1434 sq.ft. of system area of operation, including 30% for the sloped ceiling. The building also has a skylight (50 sq.ft approx.) , the maximum height on the skylight is 25’-0” above the finished floor. If this height is considered, the system area of operation requirement increases to 1950 sq.ft. One sprinkler head will provide coverage for the skylight.
So my question or confusion is- do I have to take into consideration the skylight height when calculating the design area reduction for quick response sprinklers? As the area of skylight is very small compared to rest of the room, I am not sure if this should dictate the system area of operation.

An interpretation on this code section would be appreciated.

Thank you !

 

[MGXFP]

I have been told by one AHJ that skylight height is not ceiling or roof height. However, I went back and calculated it both ways in a scenario similar to yours just in case.

 

[MedullaOblongata]

I have talked to few of the AHJs and pretty much this subject remains unclear. I have tried doing it both ways, but I'm trying to get a solid answer to make my self clear on this issue.
Thanks

 

[MedullaOblongata]

Well got an answer to that .. It can be considered as a protected ceiling pocket and its height ignored while considering ceiling or roof height.

 

[chicopee]

Did you check the explanation section at the end of NFPA13? I don't have those NFPA codes anymore but I do remember those sections.