Office buildings look like an easy brief: low fire load, compartmented floors and trained occupants. In practice, most office defects come from exactly that sense of ease. Concealed ceiling voids, raised floors, archive rooms, car park levels and tenant fit-outs are what undo an otherwise sound design.
This guide brings together hazard classification, system selection, water supply, the detection and smoke control interface, and the Turkish regulatory points for a typical multi-storey office building.
Hazard classification: NFPA 13 and EN 12845 side by side
The two standards place offices differently. NFPA 13 generally treats office areas as Light Hazard. EN 12845 restricts Light Hazard to low-combustibility spaces divided into small, fire-resisting compartments, so open-plan office floors are usually designed as OH1. Classify area by area rather than for the building as a whole.
| Area | NFPA 13 (typical) | EN 12845 (typical) | Note |
|---|---|---|---|
| Open-plan and cellular offices, meeting rooms | Light Hazard | OH1 (LH if conditions are met) | Confirm the EN compartment conditions in Annex A |
| Archive and document stores | OH2 (depending on pile and shelf height) | OH2–OH3 or storage criteria | High-shelf archives are assessed as storage |
| Enclosed car park | OH1 | OH2 | Dry system may be needed (freezing) |
| Kitchen and servery | OH1 | OH1 | Separate hood suppression system |
| Plant and electrical rooms | OH1 | OH1 | Assess separately if generator fuel is present |
| Server / comms room | Light Hazard + optional gaseous system | OH1 + optional gaseous system | Sprinklers stay; gas is supplementary |
Typical values: NFPA 13 Light Hazard is 4.1 mm/min (0.10 gpm/ft²) over 139 m² (1,500 ft²); EN 12845 OH1 is 5.0 mm/min over a 72 m² area of operation. On mixed floors, check the most demanding area hydraulically on its own. For a quick first pass use the NFPA 13 hazard classification tool and the EN 12845 hazard class finder.
System selection
- Wet pipe: the default for heated office floors. NFPA 13 requires quick-response sprinklers in Light Hazard areas.
- Dry pipe or pre-action sections: for unheated car park ramps, open loading bays and canopies. For short runs into cold areas, dry pendent sprinklers are an option.
- Gaseous suppression: for server, UPS and critical archive rooms, in addition to sprinklers. See the clean agent system design guide.
- Kitchen hood suppression: a wet chemical system for cooking-oil fires in the staff restaurant.
Concealed spaces
Ceiling voids and raised-floor voids are the blind spot of office projects. NFPA 13 requires sprinklers in concealed spaces that contain combustibles or exceed certain depths, with exceptions for non-combustible construction and limited combustible loading. EN 12845 likewise calls for protection depending on void depth and the combustibles inside. In cable-heavy offices, treating these voids as "non-combustible" is rarely realistic; decide together with the architectural and electrical teams.
Water supply and pumps
The hydraulic demand of an office building is usually set by the car park and archive areas, not the office floors. In tall buildings, pressure zoning (PRV stations or booster pumps) drives the riser design; the high-rise sprinkler and standpipe guide covers this in detail.
- Tank volume: sprinkler demand plus hose/hydrant demand multiplied by duration. For a first estimate use the fire water tank sizing calculator.
- Pumps: confirm electric duty plus diesel standby, or twin electric on independent supplies, with the authority and the insurer.
- Suction: verify suction conditions in a basement pump room with the fire pump NPSH calculator.
Detection, alarm and smoke control interface
In an office building the sprinkler system is an input to the fire alarm system. Each floor and zone should have a flow switch and a monitored zone valve, each shown as a separate address on the fire alarm panel.
- Zone alignment: sprinkler, detection and smoke control zones should follow the same floor and compartment boundaries. Mismatched boundaries trigger the wrong smoke scenario.
- Stair pressurisation and smoke extract: start automatically on alarm; the sprinkler flow signal can serve as confirmation.
- Atria and voids: openings between floors need smoke control; for an initial size use the smoke vent area calculator.
- Lift recall, door hold-open release, HVAC shutdown: write a cause-and-effect matrix and test it end to end at commissioning.
For detection design see the fire alarm system design guide.
Turkey: points under the BYKHY
The Turkish fire regulation (BYKHY) ties sprinkler requirements to building height, occupancy class and area thresholds. For offices, the practical drivers are the high-rise threshold, enclosed car parks and the escape route layout. Confirm threshold values against the current text.
- Which buildings need sprinklers: buildings requiring sprinklers in Turkey
- High-rise requirements: high-rise fire requirements in Turkey
- Escape routes: escape routes and stairs
- Car park levels: car park fire protection in Turkey
International tenants or insurers may ask for NFPA or FM Global. In that case the BYKHY is the minimum and the design must meet whichever requirement is stricter.
Common site mistakes
- Fit-outs that break the sprinkler layout. New partitions split coverage and leave a room without a sprinkler.
- Unprotected ceiling voids. As cable loads grow, the "non-combustible void" assumption no longer holds.
- Archives designed as offices. Mobile shelving and tall shelves cannot be protected at office densities.
- Frozen pipes on car park ramps. Wet pipes burst on unheated ramps.
- Sprinklers removed from the server room. Heads are taken out once a gas system is installed; this is generally unacceptable to the standard and the insurer.
- No cause-and-effect test. The alarm sounds, but the pressurisation fan or damper never moves.
Design checklist
| Check | What to look at |
|---|---|
| Hazard class | NFPA and EN class per area; archive and car park separate |
| Concealed spaces | Combustible load, depth and exception conditions above ceilings and below floors |
| Sprinkler type | Quick response in Light Hazard; temperature rating in the car park |
| Freezing | Dry or pre-action for ramps, loading bays and roof-level pipework |
| Water supply | Most demanding area plus hose demand; tank volume and duration |
| Pressure zoning | PRVs or booster pumps and the maximum pressure limit in tall buildings |
| Zone alignment | Sprinkler, detection and smoke zones on the same boundaries |
| Cause and effect | Pressurisation, smoke extract, lifts, doors, HVAC |
| Flexibility | Grid and pipe capacity that tolerate tenant fit-outs |
Leave headroom for fit-outs. Office buildings are re-partitioned many times over their life. Sizing mains and zone feeds with some hydraulic margin is far cheaper than reopening the whole calculation at every fit-out.
Frequently Asked Questions
What hazard class is an office under NFPA 13?
Office areas are generally Light Hazard. Archives, car parks, kitchens and plant rooms usually fall into Ordinary Hazard groups, so classification is done area by area.
Why are offices often OH1 under EN 12845?
EN 12845 limits Light Hazard to low-combustibility spaces divided into small, fire-resisting compartments. Open-plan floors rarely meet this, so they are usually designed as OH1.
Do ceiling voids need sprinklers?
Usually yes if the void contains combustibles or exceeds the depth limit in the standard. Exceptions depend on non-combustible construction and limited combustible loading, which cable-heavy offices often fail to meet.
Can sprinklers be removed from a server room once a gas system is installed?
Generally not. The gaseous system is supplementary; removing sprinklers needs separate approval under the standard and from the insurer, and is usually refused.
SprinkCalc — Fire Sprinkler Design Across Three Standards
SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.
Download SprinkCalc on the App StoreNFPA 13 (sprinkler design), NFPA 72 (detection and alarm), NFPA 92 (smoke control), EN 12845 (Annex A typical hazard classes), Turkish BYKHY. Confirm numerical thresholds against the current edition and the authority having jurisdiction. The findings here are typical defect patterns, not an account of events at any particular site.