EN 12845 Concealed Space Pipework and Sprinklers

Concealed spaces such as the space above a suspended ceiling, below a raised floor and in a roof void are covered in two separate places in EN 12845: whether protection is required is in Clause 5.4, and how the pipework is to be arranged is in Clause 17.3. There is no subclause 7.7 under Clause 7; Clause 7 is headed "Hydraulic design criteria" and consists of 7.1, 7.2 and 7.3. Source: TS EN 12845+A2:2026, Clause 5.4, EN p.30 and Clause 17.3, EN p.114-115.

Clause 5.4: is protection required

The standard sets a single threshold and a decision with two branches (EN p.30):

• Where the height of a concealed space in the roof or in the floor exceeds 0.8 m, those spaces shall be sprinkler protected. The height is measured between the underside of the roof and the top of the suspended ceiling, or between the floor and the underside of the raised floor.
• Where the height does not exceed 0.8 m, the spaces shall be sprinkler protected only if they contain combustible material or are constructed of combustible material. Single phase electric cables below 250 V, at most 15 per tray, are permitted.
• The protection in the concealed space is designed to LH where the main hazard class is LH, and to OH1 in all other cases. For the pipework arrangement see 17.3.

These three sentences are the whole of Clause 5.4. The resulting decision table is:

Three points to note:

1. The criterion is whether combustible material is present; the standard defines no intermediate category such as "limited combustibility".
2. The criterion is not the fire resistance class of the enclosing construction (for example REI 60); it is whether it is combustible.
3. In spaces higher than 0.8 m the content is not considered; protection is required in all cases.

The numerical limit of the cable exception should be read together with Clause 10.8.2, which covers the electrical installation: E 90 fire resistant cables may be installed in suspended ceiling voids conforming to 5.4 immediately below the structural ceiling (EN p.65).

Clause 17.3: pipework arrangement

Clause 17.3.1 (EN p.114): where sprinkler protection is required in concealed spaces such as suspended ceilings and floors, the pipework is designed as follows.

These two clauses are the most frequently overlooked part of concealed space design: a concealed space above an occupancy other than OH cannot share pipework with the sprinklers on the floor below.

Clause 17.1.5 (EN p.112) adds a general warning: pipes are installed so that they are readily accessible for repairs and alterations and shall not be embedded in concrete floors or ceilings. Wherever possible, pipework should not be installed in concealed spaces which make inspection, repair and alteration difficult.

Pipe supports

Clause 17.2.2 (EN p.113) gives the support spacing independently of diameter:

• Supports are placed at intervals of not more than 4 m on steel pipe and not more than 2 m on copper pipe.
• On pipes larger than 50 mm in diameter these distances may be increased by 50 % if either of the following conditions is met: two independent supports fixed directly to the structure; or the use of a support able to carry 50 % more load than that required in Table 40.
• Where mechanical pipe couplings are used, there is at least one support within 1 m of each coupling and at least one support on each pipe length.
• The distance from any terminal sprinkler to a support does not exceed 0.9 m on 25 mm diameter pipework and 1.2 m on pipework larger than 25 mm in diameter.
• The distance from any upright sprinkler to a support shall not be less than 0.15 m.
• Additional supports are provided on vertical pipes longer than 2 m and on pipes longer than 1 m feeding a single sprinkler.

Clause 17.2.1 (EN p.113): pipes larger than 50 mm in diameter shall not be supported from profiled steel sheet or aerated concrete floors. Supports completely encircle the pipe, are not welded to the pipe or to fittings and carry only this installation; they shall not be used to carry other installations. No part of a support may be made of combustible material and nails shall not be used.

Table 40: Design parameters for pipe supports (Clause 17.2.3, EN p.114)

Notes: when the material is heated to 200 °C the load bearing capacity shall not deteriorate by more than 25 %; the nominal cross section of threaded rods shall be increased so that the minimum cross section is still achieved; the anchor bolt lengths are given for concrete.

Sprinkler type and temperature rating

• Clause 14.2.4 (EN p.104): flat spray type sprinklers are used only in concealed spaces, above suspended open cell ceilings and in racks.
• Clause 14.2.3 (EN p.104): sidewall sprinklers shall not be installed above suspended ceilings. They also shall not be installed in HH installations (other than for the protection of corridors, cable ducts and columns) or in OH storage areas; they may be installed only below flat ceilings.
• Clause 14.2.2 (EN p.104): sprinklers without a fixed deflector, for example those with a retracted deflector that drops into position on operation, shall not be used where the ceiling slopes more than 45° from the horizontal, where the atmosphere is corrosive or has a high dust content, or in or under racks.
• Clause 14.4 (EN p.105): sprinklers are selected with a temperature rating close to but not lower than 30 °C above the highest expected ambient temperature. In unventilated concealed spaces, and below roof lights or glazed roofs, it may be necessary to install sprinklers with a higher operating temperature, up to 93 °C or 100 °C. The note states that in temperate climates a rating of 68 °C or 74 °C is suitable under normal conditions.

The standard gives no separate K factor, RTI value or spacing rule for concealed spaces. The maximum coverage area per sprinkler and the spacings are read from the general Table 19 (Clause 12.2, EN p.70): for LH, a maximum of 21.0 m² per sprinkler and S and D of not more than 4.6 m in a standard arrangement; for OH, 12.0 m² and 4.0 m; for HHP and HHS, 9.0 m² and 3.7 m.

The suspended ceiling itself and open cell ceilings

• Clause 12.4.13 (EN p.77): the use of suspended ceiling material below sprinklers is not permitted unless it is shown that the material does not impair the sprinkler protection. Where sprinklers are fitted below suspended ceilings, the ceiling material is of a type shown to be stable under fire conditions.
• Clause 12.4.14 (EN p.77-78): suspended open cell ceilings, that is ceilings with a regular open cell structure, may be used below LH and OH sprinkler installations provided all of the following conditions are met: a) the total plan open area of the ceiling, including lighting fittings, shall be not less than 70 % of the plan area of the ceiling; b) the minimum dimension of the ceiling openings shall be not less than 0.025 m or the depth of the suspended ceiling, whichever is greater; c) the structural integrity of the ceiling and of other equipment in the space above the suspended ceiling, such as lighting fittings, is not affected by the operation of the sprinkler system; d) there is no storage area below the ceiling.

In that case the sprinklers are installed as follows: the sprinkler spacing above the ceiling does not exceed 3 m; the vertical distance between the deflector of any conventional or spray sprinkler and the top of the suspended ceiling shall be not less than 0.8 m for sprinklers other than flat spray, and not less than 0.3 m where flat spray sprinklers are used; supplementary sprinklers are installed to discharge below obstructions wider than 0.8 m, such as lighting fittings. Where obstructions above the ceiling could cause significant interference with the water discharge, they are treated as a wall for the purposes of sprinkler spacing.

The obstruction rules generally lie between Clauses 12.4.6 and 12.4.14; Clause 12.5 is headed "Intermediate level sprinklers in HH occupancies" and is not about obstructions.

Sprinklers below ducts, platforms and galleries

Clause 12.4.10 (EN p.76-77): sprinklers are installed below platforms, ducts, heating panels, galleries, walkways and the like in the following cases:

• a) rectangular, wider than 0.8 m and closer than 0.15 m to an adjacent wall or partition;
• b) rectangular and wider than 1.0 m;
• c) circular, larger than 1.0 m in diameter and closer than 0.15 m to an adjacent wall or partition;
• d) circular and larger than 1.2 m in diameter.

The standard contains no rule of the form "where the gap between the duct and the ceiling is less than 0.3 m the sprinkler is placed on the side face of the duct".

Concealed spaces on the maintenance side

Clause 20.3.5 (EN p.122) covers the three yearly routine, and its scope is limited to the internal inspection of storage and pressure tanks (20.3.5.2) and the inspection and, where necessary, replacement or overhaul of all water supply stop, alarm and check valves (20.3.5.3). Sample internal examination of concealed spaces is not a routine in the standard.

The standard also gives no size or spacing for inspection hatches in concealed spaces. The access requirement follows from the general provision of Clause 17.1.5.

Field note: where the concealed space height is exactly at the 0.8 m threshold, the surfaces from which the measurement is taken (the underside of the roof, the top of the suspended ceiling) are decisive; the levels of these two surfaces should be shown clearly on the project section.

Frequently Asked Questions

Must the space above a suspended ceiling always be sprinklered?

TS EN 12845+A2:2026 Clause 5.4 (EN p.30): where the height of a concealed space in the roof or in the floor exceeds 0.8 m, those spaces shall be sprinkler protected in all cases. Where the height does not exceed 0.8 m, the spaces shall be sprinkler protected only if they contain combustible material or are constructed of combustible material. The only exception is single phase electric cables below 250 V, at most 15 per tray. The height is measured between the underside of the roof and the top of the suspended ceiling, or between the floor and the underside of the raised floor.

To which hazard class is the protection in a concealed space designed?

Clause 5.4 (EN p.30): the protection in the concealed space is designed to LH where the main hazard class is LH, and to OH1 in all other cases. This means that the OH1 design criteria apply to the concealed space even where the space below it is OH3 or HHS.

May sprinklers in a concealed space be fed from the same range pipe?

Clause 17.3.2 (EN p.114): in suspended ceilings above OH occupancies, the sprinklers above the ceiling may be fed from the same range pipes as the sprinklers below the ceiling; in pre-calculated systems the sprinklers are taken cumulatively for the purpose of determining pipe sizes. Clause 17.3.3 (EN p.115): in all other cases the sprinklers in the concealed space are fed from separate range pipes, and in pre-calculated systems the distribution pipes feeding sprinklers both inside and outside the concealed space shall not be smaller than 65 mm.

Which sprinkler type is used in a concealed space?

Clause 14.2.4 (EN p.104): flat spray type sprinklers are used only in concealed spaces, above suspended open cell ceilings and in racks. Clause 14.2.3 prohibits the installation of sidewall sprinklers above suspended ceilings. Clause 14.4 (EN p.105) states that in unventilated concealed spaces, and below roof lights or glazed roofs, it may be necessary to install sprinklers with a higher operating temperature, up to 93 °C or 100 °C.

What is the pipe support spacing in a concealed space?

Clause 17.2.2 (EN p.113): supports shall not be placed at intervals greater than 4 m on steel pipe and 2 m on copper pipe. On pipes larger than 50 mm in diameter these distances may be increased by 50 % if either of two conditions is met: two independent supports fixed directly to the structure, or the use of a support able to carry 50 % more load than that required in Table 40. Clause 17.3 covers pipework in concealed spaces but does not include support spacing.

References

• TS EN 12845+A2:2026 Clause 5.4 (EN p.30)
• TS EN 12845+A2:2026 Clause 10.8.2 (EN p.64-65)
• TS EN 12845+A2:2026 Clause 12.2, Table 19 (EN p.70)
• TS EN 12845+A2:2026 Clause 12.4.10 (EN p.76-77)
• TS EN 12845+A2:2026 Clauses 12.4.13, 12.4.14 (EN p.77-78)
• TS EN 12845+A2:2026 Clauses 14.2.2, 14.2.3, 14.2.4 (EN p.104)
• TS EN 12845+A2:2026 Clause 14.4 (EN p.105)
• TS EN 12845+A2:2026 Clause 17.1.5 (EN p.112)
• TS EN 12845+A2:2026 Clauses 17.2.1, 17.2.2 (EN p.113)
• TS EN 12845+A2:2026 Clause 17.2.3, Table 40, Clauses 17.3.1, 17.3.2 (EN p.114)
• TS EN 12845+A2:2026 Clause 17.3.3 (EN p.115)
• TS EN 12845+A2:2026 Clauses 20.3.5.2, 20.3.5.3 (EN p.122)

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