EN 12845 Annex D: Installation Zoning Rules

In large and multi-storey buildings, Annex D (normative, EN p.136-138) of TS EN 12845+A2:2026 (EN 12845:2015+A2:2026) is used to divide the area behind a single control valve set into controllable parts. This annex is short and contains sharp limits; the clauses are set out below in order and with their numerical values.

1. Scope: wet OH installations only

Clause D.1 General (EN p.136): This annex specifies the requirements specific to the sprinkler protection of buildings where zoning is adopted. It applies only to Ordinary Hazard sprinkler installations of the wet pipe type.

NOTE: zoning is optional unless required elsewhere in this standard (see Annex E and Annex F).

These two sentences draw the boundary of Annex D: it does not apply to dry, alternate and pre-action installations, and it does not apply to LH, HHP and HHS installations either.

2. The area limits permitted by zoning (Clause D.2, EN p.136)

Wet pipe Ordinary Hazard sprinkler installations may be zoned or unzoned. The protected floor area controlled by any one wet control valve set may be greater than that shown in Table 17, but subject to the following constraints:

For comparison, Table 17 (Clause 11.1.3, EN p.67) gives the maximum protected area per control valve set in wet pipe and pre-action installations: LH 10 000 m²; OH (including LH sprinklers within it) 12 000 m², other than those permitted in Annex D and Annex F; HH (including OH and LH sprinklers within it) 9 000 m². In other words, in OH installations Annex D makes it possible to go up to 120 000 m² in total, provided that this 12 000 m² limit is maintained per floor.

3. Requirements for a zoned installation (Clause D.3)

D.3.1 Extent of zones

The protected floor area per zone shall not be greater than 6 000 m².

D.3.2 Zone subsidiary stop valves

Each zone shall be independently controlled by a single zone subsidiary stop valve. The valve shall be installed in a readily accessible position at the floor level of the zone it controls. Each valve shall be secured in the open position and labelled so as to identify the area of protection it controls.

D.3.3 Flushing valves

A valve of nominal diameter not less than 20 mm shall be fitted to each zone, either at the end of the distribution pipe hydraulically most remote from the water supply or, as appropriate, at the end of each distribution pipe spur. A brass plug cap shall be fitted to the outlet of the valve.

D.3.4 Monitoring

Zoned sprinkler installations shall be fitted with tamper-proof devices to monitor the status of the following:

• a) Every stop valve capable of shutting off the flow of water to the sprinklers (including subsidiary stop valves), as fully open or not;
• b) The flow of water into each zone immediately downstream of each zone subsidiary stop valve, by means of a water flow alarm switch capable of detecting a flow equal to or greater than the flow from any single sprinkler, so as to indicate the operation of each zone;
• c) The flow of water from each main installation control valve set.

D.3.5 Zone test and drain facilities

Permanent test and drain facilities shall be provided in each zone immediately downstream of the water flow alarm switch. The test facility shall simulate the operation of any single sprinkler head. Adequate provision shall be made for the removal of the waste water.

D.3.6 Installation control valve set

The control valve set of a zoned sprinkler installation shall have two stop valves, one on each side of a single alarm valve, and a bypass connection around all three valves, of the same nominal diameter, fitted with a normally closed stop valve (Figure D.1, EN p.138). Each of the three stop valves shall be fitted with tamper-proof devices to monitor their position.

D.3.7 Installation monitoring and alarms

The monitoring devices required by D.3.4 and D.3.6 shall be electrically connected to a control and indicating panel installed in an accessible position on the premises. The indications and warnings to be given at the panel:

A means of silencing the audible alarms shall be provided at the indicating panel, but the visual indicators shall continue to operate until the installation is restored to its normal standby condition. Fire and fault signals shall be indicated in a continuously manned location (see Annex I). If, after the audible alarm has been silenced, there is any change in the alarm or fault indication at the panel, the alarm shall sound again and shall continue until it is silenced again or the panel is reset to its normal standby condition.

D.4 Block plan

Where installations are arranged in zones, the site block plan shall additionally show the locations of the zone control valves.

4. References made to Annex D

Annex D does not work on its own; two annexes make it mandatory or change its limits:

• Annex F.2 (EN p.143): where required by national regulations, installations shall be divided into zones in accordance with Annex D in order to minimise the unprotected area in the event of a failure, and the protected floor area per zone shall not exceed 2 400 m². This requirement applies only to LH and OH.
• Annex F.8 (EN p.144): only one zone of a multi-zone installation shall be shut off at any one time. When a zone is filled or refilled with water after being drained, the flushing valves in D.3.3 shall be used to check that water is present in the zone.
• Annex E (EN p.139-140): in high-rise buildings the pressure and flow requirements of the water supply are met at the outlet of the zone subsidiary stop valve in accordance with Table 6 (E.3.2); in pre-calculated systems the distribution pipes are sized by hydraulic calculation between the highest design point in the installation and the zone subsidiary stop valve at the same floor level, and the maximum friction loss shall not exceed 0.5 bar at 1 000 l/min (E.2.4).

5. Maintenance of the zone equipment

• Clause 20.3.2.7 (quarterly routine, EN p.121): all stop valves controlling the flow of water to the sprinklers shall be operated to ensure that they are in working order and securely re-set in the correct mode. This includes the stop valves at all water supplies, the valves at the alarm valves and all zone or other subsidiary stop valves.
• Clause 20.3.2.8 (EN p.121): the flow alarms (flow switches and/or pressure switches) shall be checked for correct operation.
• Table 39 (Clause 15.4, EN p.108): the minimum diameter of the valve and pipe draining a zone is 50 mm.

6. Transmission of alarms

Annex I Table I.1 (EN p.156) lists the alarm types for zoned systems separately: control valve open B, control valve partly closed B, subsidiary valve partly open B, low trunk main pressure B, water flow into installation A, water flow into zone A. Clause I.2 (EN p.156): signals from water flow alarms and/or alarm valves shall be indicated as a fire alarm (level A); technical faults shall be indicated as a fault alarm (level B).

Field note: The real gain from Annex D is operational rather than hydraulic: it reduces the area shut off during a failure or maintenance and narrows down the location of the event by means of the flow alarm. For that reason the annex focuses not on the design density but on valve, monitoring and indication discipline.

Frequently Asked Questions

To which installations does Annex D apply?

TS EN 12845+A2:2026 Clause D.1, EN p.136: this annex specifies the requirements specific to the sprinkler protection of buildings where zoning is adopted, and it applies only to Ordinary Hazard sprinkler installations of the wet pipe type. NOTE: zoning is optional unless required elsewhere in this standard (see Annex E and Annex F). Clause D.2 c): zoned installations shall not contain any hazard greater than OH3.

What is the maximum protected area per zone?

Clause D.3.1, EN p.136: the protected floor area per zone shall not be greater than 6 000 m². Clause D.2 a): the protected floor area controlled by a single wet control valve set on any one floor shall not exceed 12 000 m²; D.2 f): the protected floor area controlled by a single control valve set shall not exceed 120 000 m².

Which equipment is mandatory in each zone?

Clause D.3.2: each zone shall be independently controlled by a single zone subsidiary stop valve, installed in a readily accessible position at the floor level of the zone it controls, secured in the open position and labelled. Clause D.3.3: a flushing valve with a nominal diameter of not less than 20 mm shall be fitted to each zone, with a brass plug cap fitted to its outlet. Clause D.3.5: permanent test and drain facilities shall be provided in each zone immediately downstream of the water flow alarm switch.

Which alarms and indications are mandatory in a zoned installation?

Clause D.3.7, EN p.137: green indicators shall show that each monitored stop valve is in its correct position; an audible device and yellow indicators shall show that one or more control valve sets are not fully open, that one or more zone subsidiary stop valves are not fully open and that the static pressure in any trunk main feeding the system has fallen 0.5 bar or more below the normal static pressure; an audible device and red indicators shall show that water is flowing into the installation and into one or more zones.

How is the control valve set of a zoned installation arranged?

Clause D.3.6, EN p.137: the control valve set of a zoned sprinkler installation shall have two stop valves, one on each side of a single alarm valve, and a bypass connection around all three valves of the same nominal diameter fitted with a normally closed stop valve (Figure D.1). Each of the three stop valves shall be fitted with tamper-proof devices to monitor their position.

References

• TS EN 12845+A2:2026 (EN 12845:2015+A2:2026), Clause 11.1.3 and Table 17 (EN p.67)
• TS EN 12845+A2:2026, Clause 15.4 and Table 39 (EN p.108)
• TS EN 12845+A2:2026, Clauses 20.3.2.7 and 20.3.2.8 (EN p.121)
• TS EN 12845+A2:2026, Annex D, Clauses D.1, D.2, D.3.1, D.3.2, D.3.3, D.3.4 (EN p.136)
• TS EN 12845+A2:2026, Clauses D.3.5, D.3.6, D.3.7, D.4 (EN p.137)
• TS EN 12845+A2:2026, Figure D.1 (EN p.138)
• TS EN 12845+A2:2026, Clauses E.2.4 and E.3.2 (EN p.139-140)
• TS EN 12845+A2:2026, Clause F.2 (EN p.143) and F.8 (EN p.144)
• TS EN 12845+A2:2026, Annex I Table I.1 and Clause I.2 (EN p.156)

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