NFPA 13R and 13D Residential and Limited-Area Systems
Scope
NFPA 13R covers residential occupancies up to four stories and 60 ft above grade plane, such as apartments, hotels, and dormitories, where the code permits. NFPA 13D covers one- and two-family dwellings and manufactured homes. Neither is a substitute for NFPA 13 in a high-rise or in a mixed occupancy that exceeds the limits.
Design differences
- 13R uses listed residential sprinklers and a hydraulic design of four sprinklers; 13D uses two sprinklers. Both rely on the sprinkler’s listed flow at its coverage area, not a generic density.
- 13R may omit sprinklers in small closets and bathrooms within the listed limits; 13D has its own omission rules. Do not carry those omissions into a 13 system.
- 13R often uses a combined domestic supply; the calculation must add the domestic demand when the systems share a supply. 13D multipurpose systems require special sizing and pressure checks.
- 13R requires a control valve, flow switch, and alarm test connection; 13D has simplified but still mandatory components.
Worked example
A four-story apartment uses 13R. The most demanding four sprinklers are listed at 13 gpm each at 7 psi minimum. Sprinkler flow = 4 × 13 = 52 gpm. If the combined domestic demand is 20 gpm at 50 psi, the supply must satisfy 52 gpm plus 20 gpm at the higher pressure required by the sprinkler calculation, with elevation and pipe friction added.
Traps
Applying a 13 density/area curve to 13R; using 13R in a five-story building; forgetting the domestic demand in a combined system; omitting sprinklers where 13D rules, not 13R rules, apply; and assuming a 13R system needs no hydraulic calculation.