EN 12845 Maximum Coverage Area per Sprinkler: the LH / OH / HH Tables

Sprinkler layout is bound by two independent constraints: the area covered per sprinkler and the spacing between sprinklers. TS EN 12845+A2:2026 separates these two constraints into two tables under Clause 12.2, Table 19 for sprinklers other than sidewall and Table 20 for sidewall sprinklers. Both must be satisfied at the same time. Source: TS EN 12845+A2:2026, Clause 12.2, Tables 19-20, EN p.70-71 (TSE p.73-74).

1. Table 19: Sprinklers other than sidewall

Clause 12.2 (EN p.70) states: "The maximum area of coverage per sprinkler shall be determined in accordance with Table 19 for sprinklers other than sidewall sprinklers and Table 20 for sidewall sprinklers." The NOTE to the table states that examples are given in Figure 8 and that the dimensions S and D are the distances between sprinklers in mutually perpendicular planes.

Source: Table 19, Clause 12.2, EN p.70 (TSE p.73).

One point deserves attention: the OH row permits the staggered layout to extend to 4.6 m in the S direction, but the 4.0 m limit in the D direction is retained, and the area limit remains 12.0 m². So although 4.6 x 4.0 = 18.4 m² is geometrically possible, the area limit pulls this back to 12.0 m². Both constraints must be satisfied simultaneously.

2. Table 20: Sidewall sprinklers

In sidewall layouts the room width (w) and the room length (l) form part of the rule set:

Source: Table 20, Clause 12.2, EN p.71 (TSE p.74).

The four notes to the table:

• NOTE 1: One or more additional rows of roof or ceiling sprinklers are required.
• NOTE 2: The value of 3.4 m for OH may be increased to 3.7 m provided that the ceiling has a fire resistance of at least 120 minutes.
• NOTE 3: Sprinkler deflectors should be positioned between 0.1 m and 0.15 m below the ceiling and between 0.05 m and 0.15 m horizontally from the wall.
• NOTE 4: There should be no obstruction in the ceiling within a square extending 1.0 m along the wall on either side of the sprinkler and 1.8 m perpendicular to the wall.

The use of sidewall sprinklers is itself restricted. Clause 14.2.3 (EN p.104) prohibits sidewall sprinklers from being installed in the following locations: HH installations (except for the protection of corridors, cable ducts and columns), OH storage areas and above suspended ceilings. It also states that they "may only be installed under flat ceilings". The standard gives no ceiling height criterion here.

3. Minimum distance between sprinklers

Clause 12.3 (EN p.72): sprinklers shall not be installed at spacings of less than 2 m. Three exceptions:

• where an arrangement is made to prevent adjacent sprinklers wetting each other, which may be achieved by baffles of approximately 200 mm x 150 mm or by intervening structural elements;
• intermediate level sprinklers in racks (see Clause 12.5.3);
• escalators and stairwells (see Clause 12.4.11).

The standard sets no minimum distance between a sprinkler and a wall; Clause 12.4.1 regulates only the maximum distance to walls.

4. Maximum distance to walls

Clause 12.4.1 (EN p.72) defines the maximum distance from a sprinkler to walls and partitions as the least of the following:

• 2.0 m for standard layout;
• 2.3 m for staggered layout;
• 1.5 m where the ceiling or roof has open joists or where rafters are exposed;
• 1.5 m from the open face of open fronted buildings;
• 1.5 m where external walls are of combustible material;
• 1.5 m where external walls are of metal (with or without combustible cladding or insulation materials);
• half the maximum distance given in Tables 19 and 20.

So where the table distance for OH standard layout is 4.0 m, half of it is 2.0 m and this coincides with the 2.0 m upper limit. For LH the table distance is 4.6 m and half of it is 2.3 m, but in standard layout the 2.0 m upper limit is smaller and therefore 2.0 m applies. In a staggered LH layout 2.3 m coincides with 2.3 m.

5. Clear space to be left below the deflector

Besides the area and distance constraints there is a vertical constraint. Clause 12.1.2 (EN p.70) requires the following minimum clear space to be maintained below the deflector of roof and ceiling sprinklers:

Source: Clause 12.1.2, EN p.70 (TSE p.73).

6. Distance from the deflector to the ceiling

Clause 12.4.2 (EN p.72): sprinklers shall not be installed lower than 0.3 m below the underside of combustible ceilings, or 0.45 m below roofs or ceilings of Euroclass A1 or A2 (or the equivalent in existing national classification systems). Wherever possible the deflector is positioned between 0.075 m and 0.15 m below the ceiling or roof; this rule does not apply where ceiling, flush or recessed sprinklers are used. 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.

7. Features that disturb the area: ducts, platforms, columns, concealed spaces

Tables 19 and 20 assume a flat ceiling. Structural or services features change the area calculation:

Platforms, ducts, heating panels, galleries, walkways and similar (Clause 12.4.10, EN p.76-77). Sprinklers are installed below any of the following:

• 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.

Columns (Clause 12.4.9, EN p.76). Where a roof or ceiling sprinkler is installed closer than 0.6 m to one face of a column, another sprinkler is installed on the opposite side of the column and within 2 m of it.

Escalators and stairwells (Clause 12.4.11, EN p.77). The number of sprinklers around the perimeter of the ceiling opening is increased; sprinklers are spaced not more than 2 m and not less than 1.5 m apart. Where the minimum spacing of 1.5 m cannot be maintained because of the building design (for example beams), a smaller spacing may be used provided that adjacent sprinklers cannot wet each other. The horizontal distance between the sprinklers and the ceiling opening does not exceed 0.5 m. These sprinklers shall be capable of providing the minimum flow per sprinkler required for the protection of the rest of the ceiling. For hydraulic calculation purposes it is sufficient to consider only the sprinklers along the long side of the opening.

Concealed spaces (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 are protected by sprinklers. Where it does not exceed 0.8 m, they 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. Protection in a concealed space is to LH where the main hazard class is LH and to OH1 in all other cases.

Suspended open cell ceilings (Clause 12.4.14, EN p.77). These may be used below LH and OH installations where all four conditions are met: the total plan open area of the ceiling (including light fittings) shall not be less than 70 % of the plan area of the ceiling; the minimum dimension of the ceiling openings shall not be less than 0.025 m or the depth of the suspended ceiling, whichever is the greater; the structural integrity of the ceiling and of the equipment above it shall not be affected by the operation of the sprinklers; there shall be no storage area below the ceiling. In this case the sprinklers are installed above the ceiling; the sprinkler spacing above the ceiling does not exceed 3 m and the vertical distance between the deflector and the upper surface of the suspended ceiling is not less than 0.8 m for sprinklers other than flat spray and not less than 0.3 m for flat spray.

8. From the area limit to the number of sprinklers

Table 19 gives the maximum area per sprinkler, while the area of operation comes from Table 3. Dividing one by the other gives the minimum number of sprinklers to be included in the calculation.

Example: OH3, wet system. Table 3 (Clause 7.1, EN p.36) gives a design density of 5.0 mm/min and an area of operation of 216 m². According to Table 19 the maximum area per sprinkler for OH is 12.0 m². If the area is filled to full capacity, 216 / 12.0 = 18 sprinklers. If the actual area per sprinkler is 9.0 m², then 216 / 9.0 = 24 sprinklers enter the calculation.

The definition of density used in the hydraulic calculation is in Clause 13.4.1 (EN p.98): the discharge density is the total flow in l/min from the four adjacent sprinklers divided by the area in m² covered by those four sprinklers. Where fewer than four sprinklers are in open connection, the lowest value of the flow from any one sprinkler is divided by the area covered by that sprinkler. The area covered by each sprinkler is defined by centre lines drawn perpendicular to and midway along the lines joining adjacent sprinklers, and by the boundary of the protected area or half the distance to the nearest sprinklers, whichever is the greater (Figure 22).

Frequently Asked Questions

What is the maximum coverage area per sprinkler in EN 12845?

TS EN 12845+A2:2026 Table 19 (Clause 12.2, EN p.70): for sprinklers other than sidewall sprinklers, LH 21.0 m², OH 12.0 m², HHP and HHS 9.0 m². For sidewall sprinklers Table 20 (EN p.71) gives LH 17.0 m² and OH 9.0 m²; sidewall sprinklers may not be used in HH installations except for the protection of corridors, cable ducts and columns (Clause 14.2.3).

What are the S and D spacings for standard and staggered layouts?

Table 19 (EN p.70): for LH, standard layout S and D 4.6 m; staggered layout S 4.6 m and D 4.6 m. For OH, standard 4.0 m; staggered S 4.6 m and D 4.0 m. For HHP and HHS, standard 3.7 m; staggered S 3.7 m and D 3.7 m.

How is the maximum distance from a sprinkler to a wall determined?

Clause 12.4.1 (EN p.72) requires the least of the following values: 2.0 m for standard layout; 2.3 m for staggered layout; 1.5 m where the ceiling or roof has open joists or where rafters are exposed; 1.5 m from the open face of open fronted buildings; 1.5 m where external walls are of combustible material; 1.5 m where external walls are of metal (with or without combustible cladding or insulation); and half the maximum distance given in Tables 19 and 20.

How close together may two sprinklers be installed?

Clause 12.3 (EN p.72): sprinklers shall not be installed at spacings of less than 2 m. There are three exceptions: where an arrangement is made to prevent adjacent sprinklers wetting each other (for example baffles of approximately 200 mm x 150 mm or intervening structural elements), intermediate level sprinklers in racks (Clause 12.5.3), and escalators and stairwells (Clause 12.4.11).

When are additional sprinklers required under ducts and platforms?

Clause 12.4.10 (EN p.76-77) lists four conditions: rectangular and more than 0.8 m wide and closer than 0.15 m to adjacent walls or partitions; rectangular and more than 1.0 m wide; circular with a diameter of more than 1.0 m and closer than 0.15 m to adjacent walls or partitions; circular with a diameter of more than 1.2 m. There is no unconditional 0.8 m threshold.

How many sprinklers are included in a 216 m² area of operation?

For OH3, Table 3 (Clause 7.1, EN p.36) gives a design density of 5.0 mm/min and an area of operation of 216 m² for wet and pre-action systems. Since Table 19 gives a maximum area per sprinkler of 12.0 m² for OH, filling the area at the maximum area per sprinkler gives 216/12 = 18 sprinklers. The actual number depends on the area per sprinkler of the real layout; Clause 13.4.1 (EN p.98) defines the density as the total discharge from the four adjacent sprinklers divided by the area they cover.

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 7.1, Table 3 LH, OH and HHP design criteria (EN p.35-36 / TSE p.38-39)
• 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 12.2, Table 19 (EN p.70 / TSE p.73)
• TS EN 12845+A2:2026 Clause 12.2, Table 20 (EN p.71 / TSE p.74)
• TS EN 12845+A2:2026 Clause 12.3 Minimum distance between sprinklers (EN p.72 / TSE p.75)
• TS EN 12845+A2:2026 Clause 12.4.1 Maximum distance to walls (EN p.72 / TSE p.75)
• 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 12.4.9 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 12.4.11 Escalators and stairwells (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 13.4.1 Design density, Figure 22 (EN p.98-99 / TSE p.101-102)
• TS EN 12845+A2:2026 Clause 14.2.3 Sidewall pattern (EN p.104 / TSE p.107)

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