In a sprinkler project the word "height" describes at least seven different quantities: ceiling height, storage height, the clearance between the ceiling sprinklers and the goods, the building's level difference, the depth of a concealed space, the vertical distance between in-rack levels and the distance from the deflector to the ceiling. Each has its own threshold and its own clause; none replaces another. This article collects every height threshold in EN 12845:2015+A2:2026 and EN 12845-2:2024 in one table, with clause and EN page references. The detail of each section is linked to the relevant article on this site.
1. Summary: seven thresholds at a glance
| Quantity | Threshold | Consequence | Source |
|---|---|---|---|
| ESFR ceiling height (ceiling-only protection) | 16.8 m | Last table row; above it, modular in-rack ESFR | EN 12845-2 Table 11, EN p.41; Clause 6.6.2.2, EN p.44-47 |
| ESFR spacing | Ceiling 9.1 m | Maximum spacing 3.7 m → 3.1 m | EN 12845-2 Clause 5.1.3.2, EN p.8 |
| CMDA warehouse building height | 12 m | Authorities are consulted | EN 12845 Clause 7.2.2.1, EN p.36 |
| Clearance between ceiling sprinklers and goods (CMDA) | 4 m | Density increase or in-rack sprinklers | EN 12845 Clause 7.2.2.3, EN p.36-37 |
| Building level difference (highest – lowest sprinkler) | 45 m | Annex E high-rise rules; OH3 at most | EN 12845 Clause 5.5, EN p.30; Clause E.1, EN p.139 |
| Concealed space (roof/floor) | 0.8 m | Above it, sprinklered in any case | EN 12845 Clause 5.4, EN p.30 |
| Vertical distance between in-rack levels | 3.5 m (CMDA) · 9.1 / 12.2 m (modular ESFR) | Number of intermediate levels | EN 12845 Clause 12.5, EN p.78-81; EN 12845-2 Clause 6.6.2.2.5, EN p.47 |
2. ESFR and CMSA: the ceiling height tables (EN 12845-2)
Table 7: ceiling / storage / minimum pressure for HHS1–HHS3
In ESFR the ceiling height is not a "permission" but a table row: for each ceiling height, Table 7 (EN p.36) states which K-factor may be used at which pressure. The HHS1–HHS3 rows are:
| Max. ceiling | Max. storage | K200 | K240 | K320 | K360 |
|---|---|---|---|---|---|
| 7.6 m | 6.1 m | 3.4 bar | 2.4 bar | 1.7 bar | 1.0 bar |
| 9.1 m | 7.6 m | 3.4 bar | 2.4 bar | 1.7 bar | 1.0 bar |
| 10.7 m | 9.1 m | 5.2 bar | 3.6 bar | 2.4 bar | 1.4 bar |
| 12.2 m | 10.7 m | – | 3.6 bar | 2.8 bar | 1.7 bar |
| 13.7 m | 12.2 m | – | – | 2.8 bar | 2.8 bar |
Reading the table: K200 up to 10.7 m, K240 up to 12.2 m, K320 and K360 up to 13.7 m ceiling for ceiling-only protection. In the HHS4 rows the pressures rise at the same ceiling heights (for example K320 at 5.2 bar and K360 at 4.1 bar under a 9.1 m ceiling); the HHS5 rows apply only to exposed expanded plastics and only with all additional requirements, including vertical barriers. For the full table and the step-by-step design: ESFR Design Criteria.
15.2 m and 16.8 m: Table 11
The last two rows of Table 7 give K400 and K480 values for 15.2 m (maximum storage 13.3 m) and 16.8 m (maximum storage 14.9 m) ceilings; Table 11 (EN p.41) lists K320, K360, K400 and K480 designs for the same heights together with the ceiling-to-thermal-element distance (325 or 425 mm) and the minimum aisle width (1.8 m at 15.2 m, 2.4 m at 16.8 m). Example: HHS1–HHS3, 16.8 m ceiling, 15.2 m storage: K400 with 9 sprinklers at 5.5 bar or K480 with 9 sprinklers at 3.8 bar.
Above 16.8 m: modular in-rack ESFR
The ceiling-only tables end at 16.8 m. For higher warehouses Clause 6.6.2.2 (EN p.44-47) defines the modular ESFR in-rack design: ESFR sprinklers are used in a modular arrangement inside the racks, the warehouse height is not limited, and the scheme applies from HHS1 to HHS5 and to open-frame racks only. The water supply must be able to serve the in-rack design separately from the ceiling design. Table 14 (EN p.47) gives the minimum flow from the most remote in-rack sprinkler: 250 l/min for K200 up to HHS3, 380 l/min for K200 up to HHS4, 455 l/min for K320 up to HHS5.
There is also an intermediate scheme: Clause 6.6.2.1.1 (EN p.42) allows, for ceilings up to 13.7 m, goods up to HHS4 in open-frame racks (STC4.1–STC4.3) to be protected with K200 or larger pendent ceiling ESFR sprinklers plus a single level of in-rack sprinklers in the longitudinal flue only.
HHS5 and the 12-sprinkler design
Clause 5.4 (EN p.33) gives two height pairs for HHS5: maximum ceiling 9.1 m with storage up to 7.6 m at 2.0 bar; maximum ceiling 12.2 m with storage up to 10.7 m at 4.1 bar (K360). Detail: HHS5 + 12-Sprinkler Design.
The 9.1 m threshold: spacing changes
Clause 5.1.3.2 (EN p.8): the minimum distance between two ESFR sprinklers is 2.4 m; the maximum spacing is 3.7 m where the ceiling does not exceed 9.1 m and 3.1 m where it does. The maximum area per sprinkler is 9.3 m², the minimum 6 m². For CMSA the maximum spacing is 3.7 m, or 3.1 m under combustible obstructed construction (Clause 5.1.3.3). Detail: ESFR/CMSA Placement and Clearance.
CMSA tables are read separately
For CMSA, Tables 15–21 (EN p.49-55) and the special commodity Tables 22–25 (EN p.57-58) give their own ceiling/storage pairs; the 16.8 m ESFR row does not carry over to CMSA. Example: Table 23, heavy roll paper, storage ≤ 7.9 m / ceiling ≤ 18 m, wet system: K160 with 15 sprinklers at 3.4 bar or K240 with 15 sprinklers at 1.5 bar. Detail: CMSA Design Criteria.
Vertical distance from deflector to ceiling
Table 2 (EN p.10) gives the maximum vertical distance of the thermal element below the ceiling by K-factor: for ESFR, 325 mm for K200, K240 and K400; 425 mm for K320, K360 and K480. The deflector is at least 100 mm below the ceiling (Clause 5.1.3.5.2). The value depends on the K-factor and on whether the ceiling is obstructed or unobstructed, not on the ceiling material.
3. CMDA (EN 12845): building, storage and clearance
12 m: consult the authorities
Clause 7.2.2.1 (EN p.36): for buildings exceeding 12 m the authorities shall be consulted. The standard does not impose a prohibition here; as the height grows, the rows of Table 4 and the 4 m clearance rule have to work together.
Table 1: maximum storage heights permitted in OH3
Clause 6.2.3 (EN p.31): goods may be stored in an OH occupancy only if the protection is designed to at least OH3, the maximum storage heights of Table 1 are not exceeded, and a single block does not exceed 50 m² with a 2.4 m clear space around it. Table 1 (EN p.32):
| Commodity category | ST1 (free-standing / block stacking) | ST2–ST6 |
|---|---|---|
| Category I | 4.0 m | 3.5 m |
| Category II | 3.0 m | 2.6 m |
| Category III | 2.1 m | 1.7 m |
| Category IV | 1.2 m | 1.2 m |
If these heights are exceeded, the storage is protected as HHS according to Clauses 6.2.4.2 and 7.2. There is no single "4 metre" threshold; it depends on category and configuration. Detail: HHS Design.
Table 4 and Table 5: maximum storage with ceiling-only protection
Clause 7.2.2.2 (EN p.36): Table 4 gives the design density and area of operation for storage types protected by roof or ceiling sprinklers only, by category and maximum storage height. The storage heights in the table are maxima; when exceeded, intermediate in-rack sprinklers are added according to Clause 7.2.3 and the ceiling criteria are taken from Table 5 (EN p.39). Example: ST4 palletised racks, Category II: 7.5 mm/min at 3.4 m, 10.0 mm/min at 4.2 m, 12.5 mm/min at 5.0 m, 15.0 mm/min at 5.6 m, 17.5 mm/min at 6.0 m (area of operation 260 m²).
The 4 m clearance rule
Clause 7.2.2.3 (EN p.36-37): where the clearance between the storage height and the ceiling sprinkler deflector exceeds 4 m, one of two options applies:
- Option 1: the density is increased by 2.5 mm/min for the first excess metre and by a further 1 mm/min for each additional metre; a minimum K115 sprinkler is used.
- Option 2: intermediate in-rack sprinklers are provided according to Clause 7.2.3.
So a 4 m clearance alone does not make in-rack sprinklers mandatory. Detail: When Are Intermediate Level Sprinklers Required?
Clear space below the deflector and deflector-to-ceiling distance
Clause 12.1.2 (EN p.70): below the deflector of roof and ceiling sprinklers a clear space of 0.3 m for flat spray sprinklers and 0.5 m otherwise is kept in LH and OH; 1.0 m in HHP and HHS. Clause 12.4.2 (EN p.72): sprinklers are not installed more than 0.3 m below the underside of combustible ceilings or 0.45 m below Euroclass A1/A2 ceilings; where possible the deflector is placed 0.075–0.15 m below the ceiling.
The ESFR and CMSA counterpart: EN 12845-2 Clause 5.1.3.7 and Clause 6.1 (EN p.33) require at least 1 m of clear space between the deflector and the top of storage; clearances greater than 4 m require no correction of the design parameters.
4. Building level difference: 45 m and Annex E
Clause 5.5 (EN p.30) and Clause E.1 (EN p.139): where the height difference between the highest and the lowest sprinkler exceeds 45 m, the high-rise requirements of Annex E apply. The annex is written for occupancies whose hazard is not greater than OH3; high-rise systems above OH3 need specific fire engineering solutions and expert advice. For the design criteria (Clause E.2), the high-rise exception to the 12 bar rule and the water supplies (Clause E.3, EN p.140): Annex E — High-Rise Requirements.
5. Concealed spaces: 0.8 m
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, the space is sprinklered in any case. Where it does not exceed 0.8 m, it is sprinklered only if it contains or is built of combustible materials; the single exception is single-phase cabling below 250 V with no more than 15 cables per tray. Protection in the concealed space is designed to LH where the main hazard class is LH and to OH1 in all other cases. Detail: Sprinklers and Pipework in Concealed Spaces.
In ESFR the suspended ceiling is also a tool: where the ceiling slope exceeds 10°, a flat, continuous, horizontal false ceiling is installed and the space above it is protected as well (EN 12845-2 Clause 5.2.1); ceilings must withstand a vertical upward thrust of 140 N/m² (Clause 5.2.2). Detail: Roof Slope, Skylights and Ventilation Limits.
6. In-rack vertical distances
| System | Maximum vertical distance between levels | Source |
|---|---|---|
| CMDA intermediate level sprinklers | 3.5 m | EN 12845 Clause 12.5, EN p.78-81 |
| Modular ESFR in-rack, HHS4 and HHS5 | 9.1 m | EN 12845-2 Clause 6.6.2.2.5, EN p.47 |
| Modular ESFR in-rack, up to HHS3 | 12.2 m | EN 12845-2 Clause 6.6.2.2.5, EN p.47 |
In CMDA the intermediate level sprinklers are positioned according to Table 21 and Figure 15; the vertical distance between rows does not exceed 3.5 m, and the top rack is included where the ceiling sprinklers are more than 4 m above the goods. In modular ESFR a vertical clearance of at least 150 mm is kept between the top of storage and the deflector; the horizontal distance between in-rack sprinklers is 0.7–1.4 m (Clause 6.6.2.2.4, EN p.45). Detail: In-Rack Sprinkler Layout ST1–ST6.
Field note: in most projects the height thresholds trigger one another. Choosing ESFR for a warehouse with a 13 m ceiling forces K320/K360 (Table 7), the spacing drops to 3.1 m because 9.1 m is exceeded (5.1.3.2), and if a suspended ceiling is added, the void above it is protected separately once it exceeds 0.8 m (5.4). If the same warehouse is protected with CMDA, being above 12 m brings the authority consultation (7.2.2.1), the Table 4 height limit and the 4 m clearance rule (7.2.2.3) into play together. Keeping these thresholds in one list at the start of the project is cheaper than changing the sprinkler type later.
Frequently Asked Questions
Up to what ceiling height can ESFR ceiling sprinklers be used?
The ceiling-only protection tables of EN 12845-2:2024 end at the 16.8 m ceiling (14.9 m storage) row: Table 11 (EN p.41) gives K320, K360, K400 and K480 designs for 15.2 m and 16.8 m; for example at 16.8 m, K400 with 9 sprinklers at 5.5 bar or K480 with 9 sprinklers at 3.8 bar. In Table 7 (EN p.36) K200 appears up to 10.7 m, K240 up to 12.2 m, and K320 and K360 up to the 13.7 m ceiling row. For higher warehouses, Clause 6.6.2.2 modular in-rack ESFR design is used; in that scheme the warehouse height is not limited.
Why is a 9.1 m ceiling height a threshold?
EN 12845-2 Clause 5.1.3.2 (EN p.8): the maximum spacing between ESFR sprinklers is 3.7 m where the ceiling does not exceed 9.1 m and 3.1 m where it does. The minimum spacing of 2.4 m, the maximum area per sprinkler of 9.3 m² and the minimum area of 6 m² are the same in both cases.
What happens when a CMDA-protected warehouse is higher than 12 m?
EN 12845:2015+A2:2026 Clause 7.2.2.1 (EN p.36): for buildings exceeding 12 m the authorities shall be consulted. The standard does not prohibit it; the maximum storage heights of Table 4 and the 4 m clearance rule of Clause 7.2.2.3 apply in addition.
From what height do the high-rise rules of Annex E apply?
EN 12845:2015+A2:2026 Clause E.1 (EN p.139) and Clause 5.5 (EN p.30): Annex E applies where the height difference between the highest and the lowest sprinkler exceeds 45 m. The annex is written for occupancies whose hazard is not greater than OH3; high-rise systems above OH3 need a specific fire engineering solution and expert advice.
When must the void above a suspended ceiling be sprinklered?
EN 12845:2015+A2:2026 Clause 5.4 (EN p.30): where the height of a concealed space in the roof or floor exceeds 0.8 m, the space shall be sprinklered in any case. Where it does not exceed 0.8 m, it is sprinklered only if it contains or is constructed of combustible materials; the exception is single-phase cables below 250 V with no more than 15 cables per tray. Protection in the concealed space is designed to LH where the main hazard is LH and to OH1 in all other cases.
References
- EN 12845-2:2024, Clauses 5.1.3.2 and 5.1.3.3 (EN p.8); Clause 5.1.3.5.2 and Table 2 (EN p.9-10); Clause 5.1.3.7 (EN p.12)
- EN 12845-2:2024, Clauses 5.2.1 and 5.2.2 (EN p.12-13); Clause 5.4 HHS5 (EN p.33); Clause 6.1 (EN p.33)
- EN 12845-2:2024, Table 7 (EN p.36), Table 11 (EN p.41), Clause 6.6.2.1.1 (EN p.42), Clause 6.6.2.2 and Tables 13-14 (EN p.44-47)
- EN 12845-2:2024, Tables 15-25 CMSA (EN p.49-58)
- EN 12845:2015+A2:2026, Clauses 5.4 and 5.5 (EN p.30); Clause 6.2.3 and Table 1 (EN p.31-32)
- EN 12845:2015+A2:2026, Clauses 7.2.2.1, 7.2.2.2, 7.2.2.3 and 7.2.3 (EN p.36-37); Table 4 and Table 5 (EN p.38-39)
- EN 12845:2015+A2:2026, Clause 12.1.2 (EN p.70); Clause 12.4.2 (EN p.72); Clause 12.5 and Table 21 (EN p.78-81)
- EN 12845:2015+A2:2026, Annex E, Clauses E.1-E.3 (EN p.139-140)
Sources are listed in the References section at the end of the article. This article is for general information; for clause numbers, threshold values and exemptions, the current published standard texts must be used, and the design must be carried out by a qualified engineer.