EN 12845 Sidewall Sprinklers

Hotel corridors, narrow offices, renovations under coffered concrete slabs — the sidewall answer when pipework cannot be run at ceiling level: maximum coverage area, number of rows, the deflector window and the field errors.

On a boutique hotel renovation the architect called us in: the corridor ceiling was nineteenth-century moulded plaster, not to be touched. When I explained that pendent sprinklers could not be hung from it, the first reaction was panic, followed by "can't you feed it from the wall?" EN 12845 answers that clearly — the sidewall pattern exists for exactly this situation.

This article covers when and how sidewall heads are used, working through the coverage table and the placement rules around them.

When is sidewall the right decision?

A sidewall sprinkler throws water horizontally into the room as a spray cone from the wall. Unlike a pendent or upright head it needs no ceiling plenum. The typical applications:

• Hotel and dormitory rooms and corridors — quiet, ductless ceilings above bedrooms, and no ceiling void in the corridor.
• Strengthened renovations of existing buildings — coffered concrete slabs or historic ceilings where drilling for pipe supports is not permitted.
• Narrow offices and counters — room depth below 3.7 m, where a single sidewall row suffices.
• Plant rooms and generator rooms — where ceiling-mounted equipment leaves no room for pipe supports.

Sidewall is chosen where it is a necessity rather than a preference. A pendent head sprays downward from the ceiling and is more efficient hydraulically and in distribution; the horizontal throw of a sidewall narrows the maximum coverage area and pushes K-factor and pressure requirements slightly harder.

Coverage area and room width

The standard sets the maximum coverage area per sprinkler from a table specific to sidewall heads, which permits only two hazard classes: LH and OH. Sidewall heads are not used in HHP and HHS; storage and process hazards are protected with pendent or upright heads.

Hazard	Max. area per sprinkler	Spacing along the wall	Distance to end wall	Room width (w)	Rows / pattern
LH	17.0 m²	4.6 m	2.3 m	w ≤ 3.7 m	1 row
LH	17.0 m²	4.6 m	2.3 m	3.7 < w ≤ 7.4 m, l ≤ 9.2 m	2 rows, standard
LH	17.0 m²	4.6 m	2.3 m	3.7 < w ≤ 7.4 m, l > 9.2 m	2 rows, staggered
LH	17.0 m²	4.6 m	2.3 m	w > 7.4 m	2 rows plus ceiling sprinklers
OH	9.0 m²	3.4 m	1.8 m	w ≤ 3.7 m	1 row
OH	9.0 m²	3.4 m	1.8 m	3.7 < w ≤ 7.4 m, l ≤ 6.8 m	2 rows, standard
OH	9.0 m²	3.4 m	1.8 m	3.7 < w ≤ 7.4 m, l > 6.8 m	2 rows, staggered
OH	9.0 m²	3.4 m	1.8 m	w > 7.4 m	2 rows plus ceiling sprinklers

A useful concession: in OH, the 3.4 m spacing may be increased to 3.7 m where the ceiling has at least 120 minutes of fire resistance. If a hotel corridor has an REI 120 plasterboard ceiling, the heads sit at 3.7 m spacing — a 60 cm difference that visibly reduces the sprinkler count.

The deflector window

Two notes carry the numbers most often skipped in practice; most errors originate here.

• Deflector position: 0.10–0.15 m below the ceiling and 0.05–0.15 m horizontally clear of the wall. Set below that window, the spray never reaches the underside of the ceiling and cannot travel along it; set above it, the horizontal throw is disrupted.
• The clear zone in front: there must be no obstruction below the ceiling within 1.0 m either side of the sprinkler along the wall — 2.0 m in total — and 1.8 m in from the wall. Beams, air diffusers, acoustic panels and boxed ceilings all fall into this window; if one does, move the sprinkler or remove the obstruction.

A sidewall head is not subject to the usual maximum wall distance rule — it is on the wall. But the surrounding placement rules for canopies, skylights and false ceilings under beams still apply. In a corridor beneath a skylight in particular, the ceiling height difference may require a separate head.

K-factor selection

Sidewall heads appear in the same K-factor list as other sprinklers:

• LH: K57 for sidewall, at a density of 2.25 mm/min.
• OH: K80 or K115 for sidewall, at a density of 5.0 mm/min.

K57 is commonly used in LH hotel rooms, but the end-of-line pressure needed to serve 4.6 m spacing and 17 m² coverage should never be assumed without a hydraulic calculation — in a long corridor the last head can easily exceed 1.5 bar. Staying with K80 in OH is both typical from manufacturers and gives a more comfortable pressure in the density × area calculation.

Worked example — hotel corridor, single LH row

A boutique hotel corridor 24 m long and 1.8 m wide: room width w = 1.8 m falls into the "w ≤ 3.7 m" row, so a single sidewall row is sufficient at the LH density of 2.25 mm/min.

• Maximum spacing along the wall 4.6 m. Over 24 m with 2.3 m at each end: 24 − 2 × 2.3 = 19.4 m, which takes 5 sprinklers at 4.6 m spacing (four gaps of 4.6 m = 18.4 m, within the limit).
• Coverage per head: 4.6 × 1.8 = 8.28 m², well below the 17.0 m² limit.
• Deflector 12 cm below the ceiling, 10 cm clear of the wall. K57.
• The hydraulic calculation runs four sprinklers over the 84 m² LH area of operation; the end-of-line pressure typically closes at 0.7–1.0 bar.

The architect approves without a single hole in the plaster moulding, and the owner gets the invisible system they wanted.

Field error — sloped ceiling, wrong side

We fitted sidewall heads in a mansard roof space where the ceiling sloped downward from the wall into the room. The first layout placed the sprinklers on the low wall — and measuring the clear zone showed that the ceiling slope blocked the 1.8 m perpendicular window, with the spray hitting the ceiling. The fix was to move the heads to the high wall so the spray ran parallel beneath the sloping ceiling. This is the sidewall version of the rule that deflectors must be parallel to the ceiling slope: in a sloped room, the throw direction must not fight the slope.

Comparison with NFPA 13

NFPA 13 separates standard spray sidewall heads from extended coverage sidewall (ECSW). Under NFPA 13, ECSW for light hazard allows a maximum of about 18.6 m² (200 ft²) per head with a room depth of around 4.3 m (14 ft), and about 11.1 m² (120 ft²) for ordinary hazard. EN 12845 defines no extended category — its table sets a single limit, with ECSW products falling outside it (LH 17 m², OH 9 m²). Carrying an ECSW lounge solution from an NFPA project into an EN 12845 one therefore requires a manufacturer's type approval plus authority acceptance; defaulting to two rows is the cleanest route.

Link to Turkish regulation

BYKHY requires sprinkler design to TS EN 12845 or an equivalent standard, with no additional restriction specific to the sidewall pattern — and sidewall is the most commonly chosen pattern for sprinklered escape corridors. Certifying a project with sidewall heads where pendent mounting is difficult creates no problem under BYKHY; the question a building inspector will ask is whether the clear zone is genuinely clear and whether a beam intrudes. Drawing the 2.0 × 1.8 m rectangle on the detail sheet and keeping beams and diffusers outside it is the fastest way to close that item.

Quick check list

• Is the hazard class LH or OH? (No sidewall in HHP or HHS.)
• Room width w ≤ 3.7 m gives one row; otherwise two, staggered where needed.
• Is the OH spacing 3.4 m, or 3.7 m under an REI 120 ceiling?
• Deflector 0.10–0.15 m below the ceiling, 0.05–0.15 m clear of the wall.
• Is the 2.0 × 1.8 m clear zone in front of the sprinkler genuinely clear?
• In a sloped room, does the throw run parallel to the slope?
• Hydraulics: LH 84 m² × 2.25 mm/min = 189 L/min; OH1 72 m² × 5.0 = 360 L/min minimum.

Frequently Asked Questions

When should sidewall sprinklers be used?

Where ceiling pipework is impossible — hotel corridors, historic or coffered ceilings, narrow offices, plant rooms. They are a necessity rather than a preference; pendent heads distribute better.

What coverage area do sidewall heads get?

17.0 m² for light hazard and 9.0 m² for ordinary hazard. Sidewall heads are not permitted in high hazard process or storage occupancies.

Where must the deflector sit?

0.10–0.15 m below the ceiling and 0.05–0.15 m clear of the wall, with a clear zone 2.0 m along the wall and 1.8 m into the room free of obstructions.

How wide a room can two sidewall rows cover?

Up to 7.4 m. Beyond that, two rows must be supplemented with ceiling sprinklers.

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