Fifth Story Added to a Four-Story NFPA 13R Apartment Building

No. NFPA 13R is limited to residential occupancies not exceeding four stories and not exceeding 60 ft in height above grade plane. The proposed building is five stories and 62 ft, so it exceeds both limits and must be protected throughout as an NFPA 13 system.

The consequences are not cosmetic:

• The attic omission disappears. NFPA 13 requires sprinklers in combustible concealed spaces, including combustible attic assemblies, unless a specific exception applies (for example, noncombustible or limited-combustible construction, or spaces that meet the code's dimensional and access limits). A wood-framed pitched attic will generally need protection, which means added piping, insulation or heat tracing in some climates, and a recalculated demand.
• The calculation basis changes. The 13R calculation approach and its assumptions do not carry over to a 13 design. The remote area, density, hose allowance, and sprinkler spacing criteria all have to be re-derived under NFPA 13.
• The 8 psi margin is gone. The added fifth-floor elevation alone consumes about 4.3 psi (one story at roughly 10 ft x 0.433), before any added attic piping or larger remote area is included.
• The riser and underground must be rechecked against the new demand.

The consultant's argument that the existing calculation is 'adequate for the lower floors' answers a question nobody asked. The issue is building eligibility, and it fails.

The 48 sq ft bathrooms are within the omission limit for residential bathrooms (generally 55 sq ft or less), so those omissions are defensible under 13R as long as no other condition disqualifies them.

The 30 sq ft walk-in closets are not. The residential closet omission is limited to closets of about 24 sq ft or less, so the 30 sq ft closets on every floor are a deficiency in the currently permitted design - independent of the fifth-story issue. They need sprinklers whether or not the building is upgraded.

After the upgrade to NFPA 13, the 13R-specific omission allowances no longer apply at all. The bathroom and closet omissions must be re-evaluated against the NFPA 13 rules for small concealed and noncombustible-content spaces, and the default answer is to protect them. In practice this is a small amount of piping on each floor, but it changes the number of heads per floor and therefore the hydraulic calculation, and it must be captured before the plans are resubmitted.

The practical takeaway is that the closet issue should be raised with the developer immediately and separately. Waiting for the fifth-story decision to resolve will delay a correction that is required either way.

The resubmittal should be a complete NFPA 13 package, not a markup of the 13R drawings:

1. Revised hazard and design basis for each unit type and for the corridors, including the density, remote area, and hose allowance that actually apply.
2. Full hydraulic calculation to the most remote area on the fifth floor, including the attic heads, with the elevation to the new high point and the actual backflow device loss curve.
3. Riser and underground verification - pipe sizes, valve and meter losses, and whether the existing service is adequate.
4. Attic protection design: head type, spacing, insulation clearance, and whether a dry or preaction arrangement is needed in an unheated space, plus any listed insulated or dry-type heads.
5. Closet and bathroom protection per the NFPA 13 rules, not the 13R rules.

Coordination: obtain a fresh or verified flow test at the service, not one taken for the smaller 13R demand, and confirm with the purveyor the pressure available at the actual demand flow and the meter size proposed. Ask the AHJ in writing whether a safety margin is required above the calculated demand, and whether a pump will be permitted outdoors or requires a dedicated room. If the 8 psi margin vanishes, the pump decision drives the building's mechanical space, so it must be settled before the fifth-floor framing is finalized.