EN 12845 Annex E — High-Rise Requirements

Pressure zones, twin risers, standby pumps, intermediate tanks. In a tall building, "is the sprinkler system adequate?" is answered not only by the flow-and-pressure equation but by redundancy and the evacuation sequence.

During acceptance testing of a 26-storey residential tower, sprinklers on the 24th floor were found to be receiving barely half their nominal pressure. The designer had made the numbers work for a single riser and a single pump on paper, but had never modelled real distribution losses or simultaneous sprinkler operation. The system was retrofitted with a second pump, a twin riser, and a pressure zone boundary with reducing valves at the 14th floor — nine months of work at very substantial cost. Applying Annex E at design stage would have avoided the retrofit entirely.

Annex E — the basic high-rise rules

Pressure zones

The pressure differential on a single riser is limited. EN 12845 caps the maximum water pressure applied to a sprinkler at 12 bar. As building height grows, the lower floors face excessive pressure. The solution:

• Buildings above about 50–60 m are divided into pressure zones
• Each zone spans roughly seven to ten floors, i.e. about 7 bar of differential
• Pressure reducing valves or separate pumps between zones
• A separate stop valve and flow alarm per zone

Multiple water supplies and pumps

A high-rise building cannot accept a single pump failure:

• At least two pumps: duty and standby
• Preferably an electric and diesel combination
• Pump room at low level, in a protected enclosure (REI 120)
• Tank-type supply giving 2 hours at full flow for high hazard

Twin risers

• Two parallel risers running up separate shafts
• Each floor zone fed from both risers through tee connections, in a looped design
• If one riser fails, the other carries the load
• Check valves at the connection points, preventing reverse flow

Intermediate tanks

In very tall buildings, an intermediate or roof tank is used:

• An intermediate tank mid-building or at roof level, typically 60–100 m³
• Filled continuously from the lower tank by a booster pump
• Gravity flow on sprinkler demand
• A further redundant supply, giving 30–60 min of protection even if the main pumps are lost

Pressure zone example — a 30-storey building

Zone	Floors	Height	Design solution
Zone 1	Basement to 7	0–25 m	Direct from the main pump
Zone 2	8–15	25–50 m	Main pump with pressure reducing valves
Zone 3	16–22	50–72 m	Booster pump plus intermediate tank
Zone 4	23–30	72–100 m	Upper booster pump plus roof tank

Field error — a single riser leaves 18 floors exposed

A 22-storey office building had been designed with a single riser, to save on project cost. In its sixth year, a weld defect caused a leak in the lower section of the riser and the system was out of service for four days. Even with the impairment measures in place — fire watches, a hot work ban — the protection of 22 floors existed only on paper. Nothing happened, but the insurer recorded a single-riser high-rise as a material risk and the premium rose sharply. A twin riser adds around 15 % to cost; a single riser is no longer accepted.

Pump set redundancy arrangements

N+1, standard high-rise: one duty electric plus one standby diesel, each able to meet the full design flow.

2N, above about 50 storeys: two electric plus two diesel pumps, each set fed from an independent tank, so that a single pump room fire cannot take the system down.

Intermediate boosting: a booster pump serving the upper zone only, independent of the main pump set.

Tank redundancy

• A single tank is not sufficient; twin tanks are preferred
• An interconnection plus a separate isolation valve on each tank
• While one tank is cleaned or inspected, the other maintains protection
• Total capacity equals design duration times flow (30 min LH, 60 min OH, 90–120 min high hazard)

Fire service connections in a tall building

The number and position of fire service inlets is critical:

• One inlet every 60 m around the building perimeter
• A separate inlet per riser, where twin risers are installed
• Fire service standpipes kept separate from the sprinkler riser
• Tank capacity set with reference to expected fire service attendance time

Interaction with fire compartmentation

In a tall building each floor is a separate fire compartment (REI 120). Sprinklers complement that compartmentation but do not replace it. A curtain wall facade can become a fire spread path, so spandrel walls and perimeter sprinklers are designed together. Where there is an atrium, atrium sprinklers form an additional design, coordinated with smoke control to EN 12101.

Comparison with NFPA 13 and NFPA 14

NFPA 13 sets a maximum sprinkler pressure of 175 psi (about 12 bar) for high-rise buildings — identical to EN 12845. NFPA 14 covers standpipes for fire service use, and a combined design with the NFPA 13 sprinkler riser is accepted. NFPA 20 requires two separate pumps for a high-rise, the same approach as Annex E. The NFPA side also uses express risers serving upper floors directly; EN 12845 does not define this explicitly, but it fits the zoned-pump philosophy of Annex E.

Link to Turkish regulation

BYKHY defines a building above 21.5 m as a high building, with additional measures above 30.5 m. Sprinklers are mandatory in all high buildings. Pump redundancy, separate risers and pressure zones are not written into BYKHY directly, but the requirement to comply with international standards routes back to Annex E and NFPA 14. Annex E compliance is a standard check item in insurer and fire service inspections of tall buildings. Above 51 m, automatic suppression, smoke control and two independent escape routes are assessed together.

Quick check list

• Building above 50 m — pressure zones planned.
• Each zone has its own reducing valves or booster pump.
• Twin risers in separate shafts, looped connections.
• Pump set at least N+1, electric plus diesel.
• Twin tanks, separable by isolation valves.
• Intermediate or roof tank fed by a booster pump where required.
• Fire service inlets every 60 m, one per riser.
• Fire compartments aligned with sprinkler zones.
• Emergency lighting and a graphic alarm zone map.

Frequently Asked Questions

What is the maximum sprinkler pressure?

12 bar under EN 12845, which is why buildings above roughly 50–60 m must be split into pressure zones of seven to ten floors each.

Why is a single riser no longer accepted?

Because a defect anywhere on it leaves the whole building unprotected while it is repaired. Twin risers in separate shafts add about 15 % to cost and remove that single point of failure.

What pump redundancy does a high-rise need?

At least N+1 — a duty electric pump plus a standby diesel, each able to meet full design flow. Above about 50 storeys, a 2N arrangement with independent tanks is used.

What does an intermediate tank achieve?

It provides gravity-fed protection for 30–60 min even if the main pumps are lost, and it shortens the pressure chain to the upper floors.

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