The area per sprinkler and the spacings given in Table 19 assume a flat ceiling. In real buildings beams, trusses, ducts, columns and suspended ceilings break that assumption. TS EN 12845+A2:2026 regulates these departures in the fourteen subclauses of Clause 12.4. This article brings together those that concern structural elements. Source: TS EN 12845+A2:2026, Clause 12.4, EN p.72-78 (TSE p.75-81).
1. The basic vertical constraints (Clauses 12.1.2 and 12.4.2)
| Subject | Value | Source |
|---|---|---|
| Clear space below the deflector, LH and OH, flat spray | ≥ 0.3 m | Clause 12.1.2 a), EN p.70 |
| Clear space below the deflector, LH and OH, other cases | ≥ 0.5 m | Clause 12.1.2 a), EN p.70 |
| Clear space below the deflector, HHP and HHS | ≥ 1.0 m | Clause 12.1.2 b), EN p.70 |
| Maximum mounting depth below the underside of a combustible ceiling | 0.3 m | Clause 12.4.2, EN p.72 |
| Maximum mounting depth below a Euroclass A1/A2 (or equivalent) roof or ceiling | 0.45 m | Clause 12.4.2, EN p.72 |
| Preferred deflector to ceiling spacing | 0.075 - 0.15 m | Clause 12.4.2, EN p.72 |
Clause 12.4.2 states that the preferred range of 0.075 to 0.15 m does not apply where ceiling, flush or recessed sprinklers are used, and that where the use of the maximum distances of 0.3 m and 0.45 m is unavoidable the area concerned is kept as small as possible.
2. Roof pitch (Clause 12.4.3)
Sprinklers shall be installed with their deflectors parallel to the slope of the roof or ceiling. Where the pitch is greater than 30° to the horizontal, a row of sprinklers shall be fixed at the apex or within a radial distance of not more than 0.75 m from the apex. Clause 12.4.3, EN p.72
There is a related hydraulic effect: Clause 13.4.3.1 b) (EN p.100) requires, for gridded configurations in which the range pipes run parallel to the ridge of a roof with a pitch steeper than 6°, the remote edge length of the most unfavourable area of operation to be L ≥ 2 x √A (in other gridded cases the factor is 1.2).
3. Canopies and roof lights (Clauses 12.4.4 and 12.4.5)
- Clause 12.4.4 (EN p.72): the distance from the edge of a canopy to the nearest sprinklers shall not exceed 1.5 m.
- Clause 12.4.5 (EN p.72): roof lights with a volume greater than 1 m³ measured above the normal ceiling level shall be protected by sprinklers; they need not be protected, however, where the distance from the normal ceiling level to the top of the roof light does not exceed 0.3 m, or where a tightly fitting frame and glazing flush with the roof or ceiling is installed.
4. Clause 12.4.6: Beams and similar obstructions
Where the deflector (point D in Figure 9) is positioned above the level of the underside of beams or similar obstructions, one of the following solutions shall be adopted to ensure that the effective discharge of the sprinklers is not impaired:
- a) the dimensions shown in Figure 9 shall comply with the values specified in Figure 10;
- b) the spacing requirements of Clause 12.4.7 shall be applied;
- c) sprinklers shall be installed on both sides as if the beam were a wall.
In addition:
Sprinklers shall be positioned directly above girders or beams not wider than 0.2 m, at a vertical distance of at least 0.15 m. In all cases the ceiling clearances specified in Clause 12.4.2 apply. Where none of the above solutions is practicable (for example because it results in a very large number of sprinklers), the beams may be closed off from below and sprinklers may then be installed below the flat ceiling so formed. Clause 12.4.6, EN p.73
Figure 10 relates, by sprinkler type (spray pendent, conventional upright, spray upright, flat spray, conventional pendent), the minimum horizontal distance from the beam to the sprinkler (a, on the X axis) to the height of the deflector above (+) or below (-) the beam (b, on the Y axis) (EN p.74).
5. Clause 12.4.7: Beams and bays
Where narrow bays are formed with beam centres not more than 1.5 m apart and the beam depth exceeds 450 mm in non-combustible construction (A1 and A2) or 300 mm in combustible construction above A2, the following layout shall be used (EN p.74-75):
- A row of sprinklers is installed in the centre of every third bay; another row is installed below the centre line of the beam separating the two unprotected bays (see Figures 11 and 12);
- The maximum distance between sprinklers in the other direction, that is along the bay (S in Figures 11 and 12), shall comply with the rules for the hazard class concerned (see Clause 12.2);
- Sprinklers shall be installed not more than 1 m from walls parallel to the beams and not more than 1.5 m from walls perpendicular to the beams;
- Sprinklers installed within a bay shall be positioned with their deflectors between 0.075 m and 0.15 m below the underside of the ceiling.
The last sentence of the clause sets a limit:
Where the beam depth is greater than 0.7 m the case shall be referred to the authority.
6. Clause 12.4.8: Roof trusses
Sprinklers shall be installed in accordance with one of the following (EN p.76):
| Item | Truss flange width | Sprinkler position |
|---|---|---|
| a | Not wider than 0.2 m | Directly above or below the truss |
| b | Not wider than 0.1 m | At least 0.3 m laterally from the truss members |
| c | Wider than 0.1 m | At least 0.6 m laterally from the truss members |
The point to watch is the boundary between items b and c: the lateral distance of 0.3 m is for trusses whose flange is not wider than 0.1 m. Where the flange is wider than 0.1 m, item c applies and the lateral distance becomes at least 0.6 m.
7. Columns (Clause 12.4.9)
Where roof or ceiling sprinklers are installed closer than 0.6 m to one face of a column, another sprinkler shall be installed on the opposite side of the column and within 2 m of it. Clause 12.4.9, EN p.76
8. Platforms, ducts and similar (Clause 12.4.10)
Sprinklers are installed below platforms, ducts, heating panels, galleries, walkways and similar features with the following characteristics (EN p.76-77):
- a) rectangular, more than 0.8 m wide and closer than 0.15 m to adjacent walls or partitions;
- b) rectangular and more than 1.0 m wide;
- c) circular with a diameter of more than 1.0 m and closer than 0.15 m to adjacent walls or partitions;
- d) circular and with a diameter of more than 1.2 m.
The two conditions in items a) and c) have to be met together; there is no unconditional 0.8 m threshold.
9. Vertical shafts and flues (Clause 12.4.12)
In shafts with combustible surfaces, sprinklers shall be installed at every second floor level and at the top of every trapped section. Apart from electrical wiring, at least one sprinkler shall be installed at the top of all shafts, except where the shaft is non-combustible and inaccessible and contains Euroclass A1 material (or the equivalent in existing national classification systems) (EN p.77).
10. Suspended ceilings (Clauses 12.4.13 and 12.4.14)
Clause 12.4.13 (EN p.77): the use of suspended ceiling material below sprinklers is not permitted unless it is demonstrated that the material does not impair the sprinkler protection. Where sprinklers are fitted below suspended ceilings, the ceiling material shall be of a type demonstrated to be stable under fire conditions.
Clause 12.4.14 Suspended open cell ceilings (EN p.77-78): suspended ceilings with a regular open cell construction may be used below LH and OH sprinkler installations where all of the following conditions are met:
- a) the total plan open area of the ceiling (including light fittings) shall not be less than 70 % of the plan area of the ceiling;
- b) the minimum dimension of the ceiling openings shall not be less than 0.025 m or the depth of the suspended ceilings, whichever is the greater;
- c) the structural integrity of the ceiling and of other equipment such as light fittings in the space above the suspended ceiling shall not be affected by the operation of the sprinkler system;
- d) there shall be no storage area below the ceiling.
In such cases the sprinklers are installed as follows:
- The sprinkler spacing above the ceiling shall not exceed 3 m;
- The vertical distance between the deflector of a conventional or spray sprinkler and the upper surface of the suspended ceiling shall not be less than 0.8 m for sprinklers other than flat spray, or 0.3 m where flat spray sprinklers are used;
- Supplementary sprinklers shall be installed to discharge below obstructions wider than 0.8 m (for example light fittings).
The last sentence of the clause: where obstructions above the ceiling are likely to interfere significantly with the discharge of water, they shall be treated as walls for the purpose of sprinkler spacing.
Clause 14.2.4 (EN p.104) also states that the flat spray pattern shall be used only in concealed spaces, above suspended open ceilings and in racks.
11. Concealed spaces: class of protection and pipework arrangement
Clause 5.4 (EN p.30): where the height of a concealed space in the roof or floor, measured between the underside of the roof and the top of the suspended ceiling or between the floor and the underside of a raised floor, exceeds 0.8 m, these spaces shall be protected by sprinklers. Where the height does not exceed 0.8 m, the spaces are protected only if they contain combustible material or are constructed of combustible material; electrical cables of less than 250 V, single phase and with a maximum of 15 cables per cable tray are permitted.
The class of protection:
The protection in a concealed space shall be to LH where the main hazard class is LH and to OH1 in all other cases. For the pipework arrangement see Clause 17.3. Clause 5.4, EN p.30
Clause 17.3 (EN p.114-115): where sprinkler protection is required in concealed spaces such as suspended ceilings and floors, the pipework is designed as follows:
- 17.3.2 Suspended ceilings over OH occupancies: the sprinklers above the ceiling may be supplied 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 the pipe diameters.
- 17.3.3 All other cases: the sprinklers in the concealed space shall be supplied from separate range pipes. In pre-calculated systems the diameter of the distribution pipes feeding sprinklers both inside and outside the concealed space shall not be less than 65 mm.
The general rule on accessibility of the pipework is in Clause 17.1.5 (EN p.112): pipes shall be installed so that they are readily accessible for repair and modification and shall not be embedded in concrete floors or ceilings. Wherever possible, pipes should not be run in concealed spaces that make inspection, repair and alteration difficult.
12. Order of application
When a structural obstruction is encountered, the logic of the standard itself gives the following order:
- Is the obstruction a beam or girder? Where it is not wider than 0.2 m, a sprinkler directly above it at a vertical distance of at least 0.15 m (12.4.6). Where the deflector remains above the underside of the beam, one of the options: the Figure 9/10 geometry, the 12.4.7 bay layout, or treating the beam as a wall (12.4.6 a/b/c).
- Are the bays narrow and the beams deep? Where the centres are ≤ 1.5 m apart and the depth is > 450 mm (A1/A2) or > 300 mm (combustible), the 12.4.7 layout. Where the depth is > 0.7 m, refer to the authority.
- Is the obstruction a roof truss? 12.4.8 a/b/c according to the flange width.
- Is the obstruction a column? Where it is closer than 0.6 m, an additional sprinkler on the opposite side (12.4.9).
- Is the obstruction a duct or platform? Where one of conditions 12.4.10 a-d is met, a sprinkler below it.
- Is it a suspended ceiling? 12.4.13 for sprinklers below it; 12.4.14 for open cell ceilings with sprinklers above.
- Is it a concealed space? Where it is > 0.8 m, it is protected; the class is LH or OH1 (5.4); the pipework arrangement is in 17.3.
- Where none of these can be applied: the beams are closed off from below to form a flat ceiling (last paragraph of 12.4.6).
Frequently Asked Questions
What solutions apply where the deflector is above the underside of a beam?
TS EN 12845+A2:2026 Clause 12.4.6 (EN p.73) requires one of three solutions to be adopted: a) the dimensions shown in Figure 9 shall comply with the values specified in Figure 10; b) the spacing requirements of Clause 12.4.7 shall be applied; c) sprinklers shall be installed on both sides as if the beam were a wall. In addition, sprinklers are positioned directly above beams or girders not wider than 0.2 m, at a vertical distance of at least 0.15 m. Where none of these is practicable, the beams may be closed off from below and sprinklers installed below the flat ceiling so formed.
Under what conditions does the narrow bay layout apply?
Clause 12.4.7 (EN p.74): it applies to narrow bays with beam centres not more than 1.5 m apart and a beam depth exceeding 450 mm in non-combustible construction (A1 and A2) or 300 mm in combustible construction above A2. A row of sprinklers is installed in the centre of every third bay and another row below the centre line of the beam separating the two unprotected bays.
Where are sprinklers placed in relation to a roof truss flange?
Clause 12.4.8 (EN p.76): a) directly above or below the truss where the truss flange is not wider than 0.2 m; b) at least 0.3 m laterally from the truss members where the truss flange is not wider than 0.1 m; c) at least 0.6 m laterally from the truss members where the truss flange is wider than 0.1 m.
What is the deflector distance for a suspended open cell ceiling?
Clause 12.4.14 (EN p.77): the sprinkler spacing above the ceiling does not exceed 3 m and the vertical distance between the deflector of a conventional or spray sprinkler and the UPPER surface of the suspended ceiling is not less than 0.8 m for sprinklers other than flat spray, or 0.3 m where flat spray sprinklers are used. The sprinklers are installed above the suspended ceiling.
To which class is the protection in a concealed space designed?
Clause 5.4 (EN p.30): the protection in a concealed space shall be to LH where the main hazard class is LH and to OH1 in all other cases. For the pipework arrangement see Clause 17.3. Where the height of a concealed space in the roof or floor exceeds 0.8 m, these spaces are protected by sprinklers.
What happens where the beam depth exceeds 0.7 m?
Clause 12.4.7 (EN p.75): 'Where the beam depth is greater than 0.7 m the case shall be referred to the authority.' The standard gives no numerical solution for this case.
References
- TS EN 12845+A2:2026 Clause 5.4 Protection of concealed spaces (EN p.30 / TSE p.33)
- TS EN 12845+A2:2026 Clause 12.1.2 Clear space below the deflector (EN p.70 / TSE p.73)
- TS EN 12845+A2:2026 Clause 12.4.2 Distance to the ceiling (EN p.72 / TSE p.75)
- TS EN 12845+A2:2026 Clause 12.4.3 Roof pitch (EN p.72 / TSE p.75)
- TS EN 12845+A2:2026 Clause 12.4.4 Canopies (EN p.72 / TSE p.75)
- TS EN 12845+A2:2026 Clause 12.4.5 Roof lights (EN p.72 / TSE p.75)
- TS EN 12845+A2:2026 Clause 12.4.6, Figures 9 and 10 Beams and similar obstructions (EN p.73-74 / TSE p.76-77)
- TS EN 12845+A2:2026 Clause 12.4.7, Figures 11 and 12 Beams and bays (EN p.74-75 / TSE p.77-78)
- TS EN 12845+A2:2026 Clause 12.4.8 Roof trusses (EN p.76 / TSE p.79)
- TS EN 12845+A2:2026 Clause 12.4.9 Columns (EN p.76 / TSE p.79)
- TS EN 12845+A2:2026 Clause 12.4.10 Platforms, ducts and similar (EN p.76-77 / TSE p.79-80)
- TS EN 12845+A2:2026 Clause 12.4.12 Vertical shafts and flues (EN p.77 / TSE p.80)
- TS EN 12845+A2:2026 Clause 12.4.13 Suspended ceilings (EN p.77 / TSE p.80)
- TS EN 12845+A2:2026 Clause 12.4.14 Suspended open cell ceilings (EN p.77-78 / TSE p.80-81)
- TS EN 12845+A2:2026 Clause 13.4.3.1 Shape of the area of operation (EN p.100 / TSE p.103)
- TS EN 12845+A2:2026 Clause 14.2.4 Flat spray pattern (EN p.104 / TSE p.107)
- TS EN 12845+A2:2026 Clause 17.1.5 Concealment (EN p.112 / TSE p.115)
- TS EN 12845+A2:2026 Clauses 17.3.1, 17.3.2, 17.3.3 Pipework in concealed spaces (EN p.114-115 / TSE p.117-118)
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Download MEP Calc on the App StoreTS 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.