Short answer: TS EN 12845+A2:2026 Clause F.1 General, EN p.143: where required by national regulations, the following clauses apply. In other words, Annex F is not mandatory of itself; the clauses F.2 to F.8 become binding when national regulations call it up.

Annex F (normative, EN p.143-144) of TS EN 12845+A2:2026 (EN 12845:2015+A2:2026) is entitled "additional measures to improve the reliability and availability of the system". The annex is short: eight clauses, none of them longer than a few sentences. The clauses are set out below in the order in which they appear in the standard, with their content.

1. When Annex F comes into play

Clause F.1 General (EN p.143): "Where required by national regulations, the following clauses apply."

This single sentence establishes the status of the annex: Annex F is normative, but it is not self-triggering; what brings it into application is national regulations or the contract. The same relationship is also visible in the NOTE to Annex D (Clause D.1, EN p.136): zoning is optional unless required elsewhere in this standard; Annex E and Annex F are that "elsewhere".

2. F.2 Division into zones

In order to minimise the unprotected area in the event of a failure, installations shall be divided into zones in accordance with Annex D, with a protected floor area of not more than 2 400 m² per zone.

This requirement applies only to LH and OH.

For comparison, the limit in Annex D itself (Clause D.3.1, EN p.136) is 6 000 m² per zone. When Annex F comes into play, that limit drops to 2 400 m².

3. F.3 Wet pipe installations

Sprinkler installations shall be of the wet pipe type, and any subsidiary dry pipe or alternate extension shall comply with 11.5.

Clause 11.5.2 (EN p.69) gives the limit for these extensions: the number of sprinklers in any subsidiary extension shall not exceed 100; where more than two subsidiary extensions are controlled by one control valve set, the total number of sprinklers shall not exceed 250.

4. F.4 Sprinkler type and sensitivity

Quick response sprinklers shall be used; however, standard 'A' and special response sprinklers may be used in rooms with an area of not less than 500 m² or a height of not less than 5 m.

This clause is read together with the general sensitivity rule in the body. Table 38 (Clause 14.5.1, EN p.106):

Sensitivity rating In racks Ceiling above in-rack sprinklers Dry systems and Type A pre-action All others
Standard 'A' No Yes Yes Yes
Special No Yes Yes Yes
Quick Yes Yes No Yes

In other words, the quick response requirement of F.4 and the wet pipe requirement of F.3 complement each other: quick response sprinklers cannot be used in dry systems.

5. F.5 Control valve set

During the servicing and maintenance of the installation alarm valves, the sprinkler installation shall remain fully operational in all respects.

NOTE: in some countries duplicate installation control valve sets are required.

6. F.6 Water supplies

The system shall have at least one superior single water supply.

NOTE: in some countries duplicate supplies are required.

The same wording also appears in Annex E (Clause E.3.1, EN p.140).

7. F.7 Additional measures for theatres

In theatres with a separated stage (that is, those with a safety curtain between the stage and the auditorium):

The hazard class of theatres and cinemas is OH4 under Table A.2 (EN p.125) (the "Cinemas and theatres", "Concert halls" column).

8. F.8 Additional precautions for maintenance

The Clause 20.2.2.3 (EN p.119) referred to is the water motor alarm test in the weekly routine: each water motor alarm shall be sounded for at least 30 s.

9. Clauses not to be confused with Annex F

There are two neighbouring annexes that fall outside the scope of Annex F but relate to reliability:

Field note: Annex F is not a system of "reliability levels"; it is eight independent additional requirements that are applied together when national regulations call them up. If the contract states that "Annex F shall apply", its most visible effects are that the zone area drops from 6 000 m² to 2 400 m² and that the installation has to be of the wet pipe type.

Frequently Asked Questions

When does Annex F apply?

TS EN 12845+A2:2026 Clause F.1 General, EN p.143: where required by national regulations, the following clauses apply. In other words, Annex F is not mandatory of itself; the clauses F.2 to F.8 become binding when national regulations call it up.

What area limit per zone does Annex F impose?

Clause F.2, EN p.143: in order to minimise the unprotected area in the event of a failure, installations shall be divided into zones in accordance with Annex D and the protected floor area per zone shall not exceed 2 400 m². This requirement applies only to LH and OH.

Which sprinkler type does Annex F require?

Clause F.4 Sprinkler type and sensitivity, EN p.143: quick response sprinklers shall be used; however, standard 'A' and special response sprinklers may be used in rooms with an area of not less than 500 m² or a height of not less than 5 m.

What does Annex F require of the water supply?

Clause F.6 Water supplies, EN p.143: the system shall have at least one superior single water supply. NOTE: in some countries duplicate supplies are required. Likewise Clause F.5 Control valve set: the sprinkler installation shall remain fully operational in all respects during the servicing and maintenance of the installation alarm valves; NOTE: in some countries duplicate installation control valve sets are required.

Which additional measures does Annex F impose for theatres?

Clause F.7, EN p.143: in theatres with a separated stage (those with a safety curtain between the stage and the auditorium), a drencher line controlled by a quick opening valve fitted in an accessible position shall be provided to the safety curtain. The water supply to the drenchers shall be taken from upstream of any control valve set. The stage shall be protected by a water spray installation with automatic and manual activation. Alternatively, stages with an overall height of not more than 12 m may be protected by sprinklers. All workshops, dressing rooms, scenery, store rooms and the spaces below the stage shall be sprinklered.

References

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Standards & References

TS EN 12845+A2:2026 (EN 12845:2015+A2:2026) Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance; TS EN 12845-2:2025 (EN 12845-2:2024) ESFR and CMSA sprinkler systems. Every figure in this article is taken from the published standard text; clause, table and page references are listed under References. General information only, not a substitute for the standard or for a design review.

FS

Fatih Selvi

Mechanical engineer and software developer with field experience in MEP and fire protection, working actively with NFPA, FM Global and BS EN 12845 on site projects.