Why a neighbouring sprinkler never opens when heads are set closer than 2 m: cold soldering, deflector-to-ceiling distance, and the rules for approaching walls and beams.
On a final revision to an OH3 logistics warehouse, the architect shifted a sprinkler line slightly to clear a spotlight beam below the suspended ceiling. The site measurement between two K80 pendent heads came out at 1.55 m. The contractor's view was "it's a small difference, the authority won't notice" — while actually breaking one of the firmest rules in EN 12845: if two sprinklers are closer than 2 m, the first to open cools the second, and the second never reaches its operating temperature. On site this is called cold soldering, and dozens of fire tests have confirmed it.
EN 12845:2015+A1:2019 collects the placement distances in its layout clauses. This article reads them from a site perspective: the 2 m minimum, the 0.075–0.15 m deflector clearance (with 0.3–0.45 m maxima), the limits on approaching walls and beams, and why the common 1.5 m layout is not approved.
The 2 m rule
The standard states that sprinklers shall not be installed at intervals of less than 2 m. It allows only three exceptions:
- A baffle: roughly 200 × 150 mm, a metal plate between the two heads separating their spray distribution. A structural obstruction — a beam, duct or wall — performing the same function is also accepted.
- Intermediate in-rack sprinklers — in-rack protection follows its own geometry.
- Escalator and lift shafts — here sprinklers may come as close as 1.5 m, on the same condition: adjacent heads must not wet each other.
In every other case, approving a drawing without checking the 2 m limit is a guaranteed comeback from the insurer's loss prevention report.
Cold soldering: why 2 m
A sprinkler operates when its bulb reaches 68 °C. From the moment it opens, the hot gas layer within roughly a 1.5 m radius of the deflector is cooled heavily by the spray. A neighbouring head inside that cooled envelope will never reach 68 °C, because water lands on it and the solder or bulb stays cold. If you find a closed sprinkler in the middle of a burnt-out area in post-fire photographs, this is almost always the explanation.
The 2 m figure is an average from laboratory testing; some sprinkler types work at 1.8 m, while some high-K models are marginal even at 2.4 m. EN 12845 keeps it simple with a single 2.0 m threshold. If you must come down to 1.5 m, a 200 × 150 mm baffle is mandatory, positioned between the two heads and about 0.1 m above them.
Deflector-to-ceiling distance
The second point that causes confusion. The standard gives two separate figures:
| Ceiling or roof type | Maximum (deflector to ceiling) | Preferred range |
|---|---|---|
| Combustible ceiling or roof | 0.3 m | 0.075–0.15 m |
| Euroclass A1 or A2 (non-combustible) | 0.45 m | 0.075–0.15 m |
In short: 0.075 to 0.15 m is the real target. The 0.3 m and 0.45 m figures are upper limits used only where unavoidable, and the standard says so explicitly — where the maximum distances have to be used, the area involved must be as small as possible. An authority will not approve a whole project drawn at 0.3 m; the tolerance is for small zones under ducts and beams.
Field practice: in an open-roof warehouse under steel trusses with no plasterboard ceiling, setting the deflector 100 mm below the roof sheet captures both the ceiling jet temperature and the water distribution. At 200 mm, response time lengthens by roughly 8–12 s; at 300 mm it approaches 20 s or more. That delay never appears on the calculation sheet, but it overturns your fire size assumption.
Distance from walls and facades
The maximum distance between a sprinkler and a wall or partition:
| Situation | Maximum distance |
|---|---|
| Standard square or rectangular layout | 2.0 m |
| Staggered layout | 2.3 m |
| Open joists, open lattice roof | 1.5 m |
| Open-faced building | 1.5 m |
| Combustible external wall | 1.5 m |
| Metal facade, with or without combustible lining | 1.5 m |
| Maximum spacing from the coverage table | Half of it |
The smallest applicable value governs. With a metal facade and a 4.0 m spacing from the coverage table, the maximum wall distance is the lesser of 1.5 m and 2.0 m — so 1.5 m.
Sprinklers under beams
Positioning a sprinkler under a beam is its own maze. Two rules:
- For wide beams, an X (horizontal) versus Y (vertical) relationship applies: the closer the sprinkler is to the beam, the lower its deflector must sit, so the beam does not cut the spray cone.
- Where the beam is no wider than 0.2 m, the sprinkler may be positioned directly above it, at least 0.15 m clear.
The deflector-to-ceiling rule still applies throughout; a special solution under a beam is not a licence to drop the deflector below 0.3 m.
Distance from a canopy edge
Where external loading platforms, entrance canopies or roof extensions are protected, the sprinkler must be no more than 1.5 m from the canopy edge. Otherwise fire spreads at the edge, and the spray is trapped under the canopy rather than reaching outward.
Field error — the 1.55 m layout
The project described at the start is a real case. The contractor said "I see 1.5 m spacing every day and no insurer complains". But the loss prevention report noted that the line ran at 1.55 m spacing over 16 sprinklers. A single cold soldering event would push the area of operation from 360 m² for OH4 to 540–720 m²; the pump set cannot deliver that, pressure falls, and the system collapses.
Two options: redraw the line at 2.0 m, or fit certified 200 × 150 mm baffles between every pair and return to the insurer with site photographs. On most projects redrawing is cheaper, because sourcing, welding and getting approval for 16 baffles takes longer than the redesign.
Comparison with NFPA 13
NFPA 13 sets the minimum distance for standard spray sprinklers at 1.83 m (6 ft), and requires a full-height baffle of at least 8 in (203 mm) to go below it. EN 12845 uses a round 2.0 m and a 200 × 150 mm baffle. The underlying physics is identical — cold soldering — only the tolerances differ. Minimum distances for ESFR heads are different and generally tighter in both NFPA 13 and EN 12845-2.
Turkish context
BYKHY refers to EN 12845 for sprinkler layout detail. Authorities and insurers measure these lines individually at drawing stage on large projects. Three photographs are almost always requested at site inspection:
- A tape measurement between two adjacent sprinklers (≥ 2.0 m).
- A perpendicular measurement from the deflector to the ceiling or roof sheet (0.075–0.15 m).
- A measurement to the nearest wall or beam, within the table value.
Being able to produce those three measurements without hesitation both speeds up approval and means the system runs at its design density in a real fire.
Frequently asked questions
Is there any other way to go below 2 m?
Only the three exceptions: a 200 × 150 mm baffle, intermediate in-rack heads, and escalator or lift shafts. Otherwise the 2 m rule is absolute.
Can a baffle be any piece of sheet metal?
No. It must be a certified, water-tight baffle — typically 1.5–2 mm galvanised sheet, mounted vertically at the midpoint between the heads and about 0.1 m above them. Improvised tape or cardboard baffles are never accepted.
How is 1.5 m possible in a lift shaft?
The standard allows smaller spacing in escalator and lift shafts provided adjacent sprinklers cannot wet each other — typically because a structural girder separates them. In practice this must be shown on the shaft protection drawing with the architect.
Why is dropping below 0.15 m from the ceiling a problem?
Response time depends on ceiling jet temperature. The further the deflector sits from the ceiling, the longer the hot gas layer takes to reach the bulb — so the sprinkler opens late. At 0.3 m the delay is typically 15–20 s; at 0.45 m it approaches 30 s. That is the leading cause of exceeding the design area of operation.
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Download MEP Calc on the App StoreBS EN 12845:2015+A1:2019 Fixed firefighting systems — Automatic sprinkler systems. EN 12845-2:2024 (CMSA & ESFR sprinkler systems). NFPA 13 Standard for the Installation of Sprinkler Systems. Turkish Regulation on Fire Protection of Buildings (BYKHY). FM Global Property Loss Prevention Data Sheet 2-0.