Section 10.2.1/Number of Design Sprinklers
NFPA 13 Section 10.2.1 establishes the number of sprinklers to include in hydraulic calculations based on hazard classification.
Hydraulic calculations must be based on the number of sprinklers in the design area specified by the density/area curves and tables. For light hazard, the design area is 1,500 square feet. For ordinary hazard Group 1, the design area is 1,500 square feet. For ordinary hazard Group 2, the design area is 1,500 square feet. The number of sprinklers in the design area depends on the sprinkler spacing and the shape of the most hydraulically demanding area.
Why this section exists
The hydraulic design determines the water supply requirements for the sprinkler system. The design area represents the assumed maximum area that could be involved in a fire. The system must deliver sufficient water density over this area to control the fire. Too few sprinklers in the calculation underestimates the required flow and pressure, potentially resulting in a system that cannot deliver adequate water during an actual fire.
What plan reviewers look for
Plan reviewers check the hydraulic calculation summary for the number of design sprinklers, the design area size, and the location of the most hydraulically remote area. They verify that the design area is positioned in the most demanding location (typically the area farthest from the water supply) and that the sprinkler count is consistent with the spacing shown on the drawings.
Common violations
Related NFPA 13 requirements
Section 11.2.3 covers the hydraulic calculation procedures. Section 8.5.1 covers sprinkler spacing that determines how many heads fall in the design area. Section 23.1.1 covers water supply requirements.