In warehouse fire protection projects, three details of the building envelope lock the sprinkler design directly: the slope of the roof, the roof lights (skylights) and the air movement at ceiling level. This article draws these three topics from two sources only: TS EN 12845-2:2025 (EN 12845-2:2024), for ESFR and CMSA systems; and TS EN 12845+A2:2026 (EN 12845:2015+A2:2026), for CMDA sprinklers. Every numerical value is given together with its clause number and EN page.
1. Ceiling and roof slope
ESFR and CMSA: a single limit, 10°
EN 12845-2 Clause 5.2.1 (EN p.12) states it in one sentence: the maximum ceiling slope shall not be greater than 10° (17.6%). This limit does not differ between ESFR and CMSA; the standard gives a single value.
If the slope exceeds 10°, Clause 5.2.1 defines three options:
- A flat, continuous, horizontal false ceiling is installed over the affected area and for two rows of sprinklers beyond it in every direction. The false ceiling shall comply with Clause 5.2.2, the space above the false ceiling shall be protected by sprinklers, and sprinkler protection shall be provided below it according to the relevant occupancy hazard class.
- In areas containing rack storage only, an additional in-rack level at the top of the storage is installed in addition to the in-rack sprinklers required by Clause 6.6.2.1; this level also has face sprinklers at the same spacing as the longitudinal sprinklers.
- The sprinkler system is designed in accordance with EN 12845.
Two further provisions are linked to slope. Clause 5.1.3.1 (EN p.8): the linear distance between sprinklers is measured along the slope of the ceiling, not on the projection seen from the floor. Clause 5.1.3.6 (EN p.12): sprinklers are preferably installed with the deflector parallel to the floor; where the slope is not more than 10° they may also be installed parallel to the ceiling.
On sloping and obstructed ceilings the vertical positioning is also tied to the slope:
| Case | Limit | Source |
|---|---|---|
| ESFR, slope ≤10°, vertical spacing | Shall not exceed 600 mm | 6.6.1.2 d)-f), EN p.40 |
| ESFR, if exceeded | Thermal element in a plane not more than 150 mm below the underside of the solid structural member | 6.6.1.2 f), EN p.40 |
| CMSA, slope ≤10° | Not more than 600 mm from ceiling to thermal element | 6.7.2, EN p.56 |
| CMSA, slope ≤18.5° | Not more than 450 mm from ceiling to thermal element | 6.7.2, EN p.56 |
| CMSA, if exceeded | Thermal element not more than 150 mm below the underside of the solid structural member; the resulting bays shall not exceed 28 m² | 6.7.2, EN p.56 |
CMDA: not a slope limit, but a deflector rule
EN 12845+A2 Clause 12.4.3 (EN p.72) gives no numerical maximum slope for CMDA sprinklers. The rule is this: sprinklers are installed with their deflectors parallel to the slope of the roof or ceiling; where the slope is greater than 30° to the horizontal, a row of sprinklers is fixed at the apex or within a radial distance of not more than 0.75 m from the apex.
2. Skylights (roof lights)
EN 12845-2 Clause 5.2.3 (EN p.13) sets three separate requirements for skylights:
- Resistance: the skylight shall be capable of withstanding a temperature of 300 °C for at least 5 minutes.
- Protection threshold: skylights with a volume greater than 1 m³ measured above the normal ceiling level shall be protected by sprinklers. Two exceptions: if the distance from the normal ceiling level to the top of the skylight does not exceed 0.3 m, or if there is a tight fitting frame and glazing flush with the roof or ceiling.
- Type: any supplemental sprinkler inside the skylight shall be of the same type as the sprinklers around the skylight.
The design height is governed by the same clause: where the sprinkler design is based on the building height including the skylight dome, normal spacing may be applied. Where the distance to the top of the skylight exceeds 0.3 m and the design exceeds the maximum building height, Option 1 in Figure 3 or Option 2 in Figure 4 is used; where these options are applied, the design is made for 0.3 m higher than the ceiling.
The difference between the two options lies in the elevation of the supplemental sprinklers and in the ceiling height used in the design:
| Option 1 (Figure 3, EN p.14) | Option 2 (Figure 4, EN p.15) | |
|---|---|---|
| Supplemental sprinkler type | Quick response and, where available, pendent | Quick response and, where available, pendent |
| Position | Beneath the plastic skylight | At the same elevation as the ceiling sprinklers |
| Horizontal spacing | ≤50% of the maximum permitted linear spacing | ≤50% of the maximum permitted linear spacing |
| Height used in the design | Maximum ceiling height of the plastic skylight | Maximum ceiling height of the main building |
| Hydraulic calculation | Supplemental sprinklers are not included in the ceiling design | Supplemental sprinklers are not included in the ceiling design |
The standard contains no area limit such as "maximum 5 m² per skylight" or "5% of the total roof area"; the criteria are volume (1 m³) and height (0.3 m).
On the CMDA side, EN 12845+A2 Clause 12.4.5 (EN p.72) gives the same threshold: skylights with a volume greater than 1 m³ measured above the normal ceiling level shall be protected by sprinklers; the 0.3 m and tight fitting frame exceptions are identical.
The strength of the ceiling structure also belongs to this section: Clause 5.2.2 (EN p.12) requires ceilings, sub-ceilings and suspended ceilings (including solid barriers) to be securely fixed and to withstand a vertical upward thrust of 140 N/m². Examples given are 10 mm plasterboard, corrugated and flat steel sheet and mineral ceiling tiles (EN p.13).
3. Smoke and heat vents, natural exhaust openings
EN 12845-2 Clause 5.2.4 (EN p.16) contains a clear prohibition and three conditional solutions:
- Only manually opened smoke or heat vents shall be used in ESFR or CMSA installations.
- Drop-out heat vents shall not be installed.
- Where national regulations require automatic smoke and heat vents, the ventilation system shall not impair the operation and performance of the sprinkler system. To this end, one of the following solutions is applied: 1. Relevant sprinklers are installed directly beneath the vent opening, evenly distributed, at a linear spacing of not more than 1.2 m and not more than 0.6 m from the edge of the vent. These sprinklers shall have at least the same k-factor and orientation as the adjacent ceiling sprinklers and shall be fed by pipes not smaller than the ceiling level range pipes. Where they are installed inside a skylight, the minimum and maximum vertical distance requirements of Clause 5.1.3.5.2 between the deflector and the closed skylight do not apply. These sprinklers are not added to the hydraulic design of the ceiling system. 2. The vents are fitted with a standard response thermal element rated nominally 141 °C or higher. 3. The automatic smoke vents are activated individually.
For natural exhaust openings, Clause 5.2.5 (EN p.17) introduces a similar arrangement: sprinklers are installed directly beneath the opening at a linear spacing of not more than 1.2 m and not more than 0.6 m from the edge; here, however, the vertical distance requirements of Clause 5.1.3.5.2 between the deflector and the top of the vent do apply. These sprinklers are likewise not included in the ceiling design.
4. Ventilation: the 1.5 m/s limit
The ventilation provision of the standard is not a delay time but a velocity limit.
Horizontal air flow (5.2.6.1, EN p.18-19)
Ventilation equipment shall be arranged so that the air velocity at any ceiling level sprinkler does not exceed 1.5 m/s, or so that it stops automatically on early fire detection. Where exceeding 1.5 m/s cannot be avoided, one of the following options is applied:
- Flame detectors are installed at ceiling level; the detectors are arranged to monitor the area within a radius of 3.0 m from all affected sprinklers.
- Linear heat detection is installed inside the storage racks; it is placed at the top of the rack structure in all transverse flue spaces within a radius of 3.0 m of any sprinkler affected by the high velocity. The nominal temperature rating shall be as low as the ambient conditions permit.
Both detector types are arranged to shut off the air flow automatically when they activate.
Storage directly beneath the openings is not permitted. The horizontal distance L (m) between the stored goods and the perimeter of the intake opening:
L = ½S + d, where S = sprinkler spacing (m), d = ventilation duct diameter (m).
A horizontal sub-ceiling is installed beneath the openings and sprinklers are placed below the sub-ceiling according to the normal spacing requirements. The minimum diameter or cross-sectional dimension W (m) of the sub-ceiling:
- If the flow rate is known: W = Q / (283 min/m × h)
- If the flow rate is not known: W = 2.6 A* / h
where Q = ventilation flow rate (m³/min), A* = area of the ventilation opening (m²), h = vertical distance between the ceiling and the top of the sub-ceiling (m). Ceiling sprinklers shall be at a horizontal distance of at least 0.7 × the sprinkler spacing from the perimeter of the sub-ceiling.
In addition (EN p.19), extract fans and fire dampers shall close before the first sprinkler operates. The fire detection and alarm system shall be either an aspirating smoke detection system installed in all ventilation ducts extracting from the ESFR or CMSA protected risk, or a system with detection performance equivalent to an aspirating system. Flow rate in a circular duct: Q = (49 / 60) × A × V.
Vertical air flow (5.2.6.2, EN p.20)
In storage type occupancies, the air flow is arranged between the top of the storage and the horizontal plane of the ceiling level sprinklers and so that the velocity does not exceed 1.5 m/s. The standard lists six options: (1) automatic shutdown on water flow alarm; (2) automatic shutdown by flame detection monitoring a 3.0 m radius; (3) a 30% increase in the design area in a wet system; (4) a flat continuous false ceiling with sprinklers below it on the same range pipe and spacing; (5) automatic shutdown by line type detection in the transverse flue spaces at the top of the racks; (6) installing the ceiling level sprinklers as in-rack sprinklers at the flue intersections.
Field note: The common logic behind these provisions is that every factor which disturbs the hot gas reaching the thermal element of the sprinkler and the water droplet descending onto the fire is either removed at source or stopped by detection. If envelope decisions (slope, skylights, vents, fans) are not locked at the start of the project, the choice of sprinkler type may be invalidated later on.
Frequently Asked Questions
What is the maximum ceiling slope permitted in ESFR and CMSA systems?
TS EN 12845-2:2025 (EN 12845-2:2024) Clause 5.2.1, EN p.12: the maximum ceiling slope shall not exceed 10° (17.6%). This limit is the same for both ESFR and CMSA; there is no separate 'ESFR 5%' limit in the standard. If the slope exceeds 10°, the standard gives three options: a flat continuous suspended ceiling, an additional in-rack level in rack storage only, or design in accordance with EN 12845.
When must a skylight be protected by sprinklers?
Clause 5.2.3, EN p.13: skylights with a volume greater than 1 m³ measured above the normal ceiling level shall be protected by sprinklers. Exception: if the distance from the normal ceiling level to the top of the skylight does not exceed 0.3 m, or if there is a tight fitting frame and glazing flush with the roof or ceiling. The same rule also appears in EN 12845+A2:2026 Clause 12.4.5, EN p.72.
What type shall the sprinklers added under a skylight be?
EN 12845-2:2024 Figure 3 (EN p.14) and Figure 4 (EN p.15): the supplemental sprinklers shall be quick response and, where available, pendent, and shall not be included in the ceiling level sprinkler design.
Can automatic smoke vents be used in a building protected by ESFR or CMSA?
Clause 5.2.4, EN p.16: only manually opened smoke or heat vents shall be used in ESFR or CMSA installations; drop-out heat vents shall not be installed. Where national regulations require automatic vents, one of three solutions applies: sprinklers beneath the vent opening at a linear spacing of not more than 1.2 m and not more than 0.6 m from the edge; or vents with standard response thermal elements rated 141 °C or higher; or individual activation of the vents.
What is the maximum air velocity permitted at ceiling level?
Clause 5.2.6.1, EN p.18: ventilation equipment shall be arranged so that the air velocity at any ceiling level sprinkler does not exceed 1.5 m/s, or shall stop automatically on early fire detection. Clause 5.2.6.2, EN p.20 repeats the same 1.5 m/s limit for vertical air flow.
Is there a roof slope limit for CMDA (EN 12845-1) sprinklers?
TS EN 12845+A2:2026 Clause 12.4.3, EN p.72: sprinklers are installed with their deflectors parallel to the slope of the roof or ceiling. Where the slope is greater than 30° to the horizontal, a row of sprinklers is fixed at the apex or within a radial distance of not more than 0.75 m from the apex. This clause gives no numerical upper slope limit.
References
- TS EN 12845-2:2025 (EN 12845-2:2024), Clauses 5.1.3.1 and 5.1.3.2/5.1.3.3 (EN p.8)
- TS EN 12845-2:2025, Clause 5.1.3.5.2 (EN p.9) and Table 2 (EN p.10)
- TS EN 12845-2:2025, Clauses 5.1.3.6, 5.1.3.7, 5.1.3.8 and 5.2.1, 5.2.2 (EN p.12)
- TS EN 12845-2:2025, Clause 5.2.2 example and Clause 5.2.3 Skylights (EN p.13)
- TS EN 12845-2:2025, Figure 3 - Skylight Option 1 (EN p.14)
- TS EN 12845-2:2025, Figure 4 - Skylight Option 2 (EN p.15)
- TS EN 12845-2:2025, Clause 5.2.4 Heat and smoke vents, Figure 5 (EN p.16)
- TS EN 12845-2:2025, Clause 5.2.5 Natural exhaust openings, Figure 6 (EN p.17)
- TS EN 12845-2:2025, Clause 5.2.6.1 Horizontal air flow (EN p.18-19)
- TS EN 12845-2:2025, Clause 5.2.6.2 Vertical air flow (EN p.20)
- TS EN 12845-2:2025, Clause 6.6.1.2 and Figure 24 (EN p.38-40)
- TS EN 12845-2:2025, Clause 6.7.2 and Figure 32 (EN p.55-56)
- TS EN 12845+A2:2026 (EN 12845:2015+A2:2026), Clauses 12.4.3 and 12.4.5 (EN p.72)
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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.