The most frequently debated question in warehouse sprinkler design is whether ceiling sprinklers alone are sufficient. TS EN 12845+A2:2026 ties that decision to three inputs: the storage configuration (ST1-ST6), the hazard class and the stacking height. Only the text of the standard itself has been used in this article. Source: TS EN 12845+A2:2026, Clause 6.3.2, Table 2, Clause 7.2.2, Clause 7.2.3 and Clause 12.5.
What are ST1-ST6?
Clause 6.3.2 (TS p.36 / EN p.33) defines the storage configurations as follows:
| Code | Definition |
|---|---|
| ST1 | Free standing or block stacking |
| ST2 | Single row post pallet, with aisles not narrower than 2.4 m |
| ST3 | Multiple row (including double row) post pallet |
| ST4 | Palletized rack, beam pallet racking |
| ST5 | Solid or slatted shelving of width 1 m and below |
| ST6 | Solid or slatted shelving wider than 1 m and not exceeding 6 m |
The NOTE to the same clause states that specific height limits linked to the type of sprinkler system exist for each storage method, and directs the reader to Clause 7.2.
Table 2: which configuration calls for in-rack sprinklers
Table 2 (TS p.37 / EN p.34) gives, for each configuration, the maximum stack block area, the aisle width and the minimum separation clearance around the block. The in-rack sprinkler provision appears only in the ST4, ST5 and ST6 rows:
| Configuration | Hazard | Condition | Maximum block area (m²) | Aisle (m) | Separation clearance (m) |
|---|---|---|---|---|---|
| ST1 | OH / HH | - | 50 / 150 | not applicable | 2.4 |
| ST2 | OH / HH | - | 50 / unlimited | 2.4 or more | 2.4 / not applicable |
| ST3 | OH / HH | - | 50 / 150 | not applicable | 2.4 |
| ST4 | HH | without intermediate level in-rack sprinklers (footnotes b, c) | unlimited | 1.2 or more | not applicable |
| ST4 | HH | with intermediate level in-rack sprinklers (footnote d) | unlimited | less than 1.2 | not applicable |
| ST4 | HH | with intermediate level in-rack sprinklers (footnote e) | unlimited | greater than 1.2, less than 2.4 | not applicable |
| ST4 | HH | with intermediate level in-rack sprinklers (footnote f) | unlimited | 2.4 or more | not applicable |
| ST5 | HH | without intermediate level in-rack sprinklers (footnotes b, c) | 150 | less than 1.2 | 2.4 |
| ST5 | HH | with intermediate level in-rack sprinklers (footnote d) | 150 | less than 1.2 | 2.4 |
| ST5 | HH | with intermediate level in-rack sprinklers (footnote g) | unlimited | 1.2 or more | not applicable |
| ST6 | OH | HH protection is used | - | - | - |
| ST6 | HH | with intermediate level in-rack sprinklers (footnotes c, h) | 150 | 1.2 | 2.4 |
Two footnotes to the table govern the design directly:
- Footnote b: intermediate level in-rack protection is recommended.
- Footnote c: this method of protection is limited to risks where the ceiling sprinklers are less than 4 m above the top level of the stored goods. Where the ceiling sprinklers are more than 4 m above the top level of the goods, intermediate level in-rack sprinklers shall be used.
- Footnote h: where it is not practicable to install intermediate sprinklers in ST6, longitudinal and transverse full height bulkheads shall be fitted inside each rack; these bulkheads shall be manufactured to EN 13501-1 Euroclass A1, A2 or the national equivalent.
When are ceiling sprinklers not enough?
Clause 7.2.2.2 (TS p.39 / EN p.36): Table 4 gives the maximum stacking heights permitted with roof or ceiling protection only, by category and configuration. Where the stacking height exceeds that limit, intermediate level in-rack sprinklers shall be installed in accordance with Clause 7.2.3.
Clause 7.2.2.3 (TS p.39-40 / EN p.36-37) defines a second trigger: where the clearance between the stacking 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 metre of excess and by a further 1 mm/min for each subsequent metre; sprinklers of at least K115 are used.
- Option 2: intermediate level in-rack sprinklers are installed in accordance with Clause 7.2.3.
Hydraulic calculation: how many sprinklers are assumed to operate?
Clause 7.2.3.3 (TS p.40 / EN p.37) is the backbone of the calculation: at each in-rack level, 3 sprinklers in the hydraulically most remote position are assumed to operate simultaneously and no more than three levels are taken into account. As regards the rack aisles:
- one rack where the aisle is 2.4 m or more,
- two racks where the aisle is between 1.2 m and 2.4 m,
- three racks where the aisle is narrower than 1.2 m.
The most onerous combination that follows is 3 x 3 x 3 = 27 in-rack sprinklers. The NOTE to the clause states explicitly that it is not necessary to assume that more than three rows operate simultaneously in the vertical plane, nor more than three rows in the horizontal plane.
On the ceiling side, Clause 7.2.3.2 (TS p.40 / EN p.37) requires a minimum of 7.5 mm/min over 260 m². Where goods are also stored above the top level of the intermediate protection, the ceiling criteria are taken from Table 5 (TS p.42 / EN p.39). In Table 5, for ST4 palletized racks the stacking height permitted above the topmost in-rack level is 3.5 m for Category I, but only 2.2 m for Category III in the 7.5 mm/min row; reaching 3.5 m in the same category requires 15.0 mm/min.
Clause 7.2.3.1: where more than 50 intermediate level sprinklers are installed in racks, they shall not be fed from the same control valve set as the ceiling sprinklers. Clause 7.2.3.4 and Clause 13.1 (TS p.85 / EN p.82): the fully calculated method is mandatory for HHS arrangements with in-rack sprinklers.
Physical layout: Clause 12.5
Clause 12.5.1 (TS p.81 / EN p.78): sprinklers protecting double row racks are placed in the longitudinal flue space, preferably at the intersection with the transverse flue. Water shall be able to penetrate into the goods: the longitudinal flue between goods placed back to back shall be at least 0.15 m, and the transverse flue between goods placed side by side at least 0.10 m. The clearance between the sprinkler deflector and the top of the stack shall be at least 0.10 m for flat spray sprinklers and 0.15 m for others.
Clause 12.5.2: the vertical distance from the floor to the lowest intermediate level, and between levels, shall not exceed 3.50 m or two tiers, whichever is the smaller. Unless all roof/ceiling sprinklers are less than 4 m above the top of the stack, an intermediate level shall be placed above the topmost storage level. In no case shall the topmost intermediate level be lower than one tier below the top of the stack.
Clause 12.5.3:
| Commodity category | Position | Maximum horizontal spacing | Horizontal x vertical product |
|---|---|---|---|
| Category I or II | Longitudinal flue, every second transverse flue intersection, staggered relative to the row above | 3.75 m | 9.8 m² |
| Category III or IV | Longitudinal flue, every transverse flue intersection | 1.9 m | 4.9 m² |
Clause 12.5.4: the number of sprinkler rows per level is determined by the total rack width; one row is provided for every 3.2 m of rack width. For racks placed back to back, the total width is the sum of the widths of the racks plus the distance between them.
Clause 12.5.5, for ST4 palletized racks and multiple row drive-through storage: single row racks not exceeding 3.2 m are protected by a single row of sprinklers; double row racks not exceeding 3.2 m by sprinklers centrally in the longitudinal flue space and at the ends of the stack; double/multiple row racks wider than 3.2 m but not exceeding 6.4 m by two rows of sprinklers spaced not more than 3.2 m apart.
Clause 12.5.6 and Table 21 (TS p.84-85 / EN p.81-82), for ST5 and ST6 solid/slatted shelving:
| Shelf width s | Sprinkler rows | Maximum spacing along the row | Maximum distance between rows |
|---|---|---|---|
| ST5: s ≤ 1.0 m | 1 | 2.8 m | - |
| ST6: 1.0 < s ≤ 3.0 m | 1 | 2.8 m | - |
| ST6: 3.0 < s ≤ 6.0 m | 2 | 2.8 m | 2.8 m |
The distance from the end of the rack parallel to the range pipes to the nearest sprinklers is half the sprinkler spacing along the range, or 1.4 m, whichever is the smaller. The vertical distance between rows shall not exceed 3.5 m.
Sprinkler selection: sensitivity, pressure, water shield
- Sensitivity: Table 38 (Clause 14.5.1, TS p.109 / EN p.106) permits only Quick response for in-rack sprinklers; Standard 'A' and Special shall not be used in racks. The same clause requires that, where sprinklers are installed in racks, the sensitivity of the ceiling sprinklers be equal to or slower than that of the rack sprinklers.
- Pressure: Clause 13.4.4 (TS p.105 / EN p.102): 1.00 bar for K115 in-rack sprinklers and 2.00 bar for K80 in-rack sprinklers.
- K-factor: Table 37a (TS p.107 / EN p.104) gives conventional, spray and flat spray types for HHS intermediate sprinklers in high piled storage, with a K-factor of 80 or 115.
- Water shield: Clause 14.7 (TS p.109 / EN p.106): sprinklers installed in racks or beneath perforated shelving/platforms shall be fitted with a metal water shield of at least 0.075 m diameter. On upright sprinklers the water shield shall not be attached directly to the deflector or yoke; bracket supports shall be designed to interfere as little as possible with the water distribution.
- Spacing exception: Clause 12.3 (TS p.75 / EN p.72) prohibits sprinklers being spaced closer than 2 m; intermediate sprinklers in racks are the exception to that prohibition.
Special cases in Annex G
Annex G (normative) tightens the in-rack rules for certain commodities:
- Pallet storage, Table G.6 (TS p.153 / EN p.150): pallets of timber and cellulosic material, and non-expanded high density polyethylene pallets with solid platforms, are protected as Category IV, with ceiling sprinklers rated 93 °C or 100 °C. For all other plastic pallets, in-rack protection is provided to Category IV, including one level above the topmost storage level, using K = 115 sprinklers at a minimum operating pressure of 3 bar; the ceiling requirement is 25 mm/min over 300 m².
- PP/PE containers, Clauses G.8.2 and G.8.3 (TS p.154 / EN p.151): polypropylene and polyethylene storage containers are classified as HHS Category IV. On ST4 palletized racks the horizontal spacing of the in-rack sprinklers shall not exceed 1.5 m and the vertical spacing shall not exceed 2 m; ceiling sprinklers shall be of 'Special' sensitivity and in-rack sprinklers of 'Special' or 'Quick' sensitivity.
- Garment storage on hangers, Clause G.3.4 (TS p.149 / EN p.146): the number of operating rack sprinklers is taken as 3 rows, 3 levels, 3 sprinklers per row.
Does ESFR remove the need for in-rack protection?
EN 12845-2:2024, Clause 6.6.1 (EN p.36) gives the ceiling only protection design tables for ESFR, while Clause 6.6.2 of the same standard covers in-rack arrangements used together with ESFR; for example, Clause 6.6.2.1.1 allows commodities up to HHS4 at ceiling heights up to 13.7 m to be protected with K200 and larger pendent ESFR ceiling sprinklers plus a single level of in-rack sprinklers in the longitudinal flue space. The Introduction to EN 12845-2 likewise states that ESFR is generally used for ceiling only protection, but that ESFR schemes using in-rack heads also exist. TS EN 12845+A2:2026, Annex P (TS p.167 / EN p.164) requires EN 12845-2 to be applied together with this document for ESFR systems.
Field note: the "4 m" dimension in footnote c to Table 2 is not breached at the design stage but in service; as the warehouse fills the stack rises, and an ST4 warehouse built without in-rack sprinklers quietly falls outside the rules. That is precisely why Clause 20.3.2.2 (TS p.123 / EN p.120) requires the quarterly routine to review the effect of any change in storage configuration on the hazard class.
Frequently Asked Questions
How many in-rack sprinklers are assumed to operate in an EN 12845 hydraulic calculation?
Clause 7.2.3.3 (TS p.40 / EN p.37): at each in-rack level, 3 sprinklers in the hydraulically most remote position are assumed to operate simultaneously, and no more than three levels are taken into account. Where the aisle width is 2.4 m or more a single rack is considered, between 1.2 m and 2.4 m two racks, and below 1.2 m three racks. The worst case is therefore 3 sprinklers x 3 levels x 3 racks = 27 sprinklers. The NOTE to the same clause states that it is not necessary to assume that more than three rows operate simultaneously in the vertical plane, nor more than three rows in the horizontal plane.
What is the minimum operating pressure for in-rack sprinklers?
Clause 13.4.4 (TS p.105 / EN p.102): 1.00 bar for K115 in-rack sprinklers and 2.00 bar for K80 in-rack sprinklers. The NOTE to Clause 7.2.3.4 also cites 2.0 bar as the minimum pressure at any operating sprinkler and refers to 13.4.4.
In which ST configuration do in-rack sprinklers become mandatory?
Under Table 2 (TS p.37 / EN p.34), in-rack (intermediate level) protection is required for ST6 in high hazard; for ST4/HH the solution without in-rack sprinklers applies to aisle widths of 1.2 m and above, while below 1.2 m intermediate level sprinklers are required. In addition, footnote c to Table 2 restricts solutions without in-rack sprinklers to risks where the ceiling sprinklers are less than 4 m above the top level of the goods; above 4 m, intermediate level in-rack sprinklers are used.
What horizontal and vertical spacing applies to in-rack sprinklers?
Clause 12.5.2 (TS p.81 / EN p.78): the vertical distance from the floor to the lowest intermediate level, and between levels, shall not exceed 3.50 m or two tiers, whichever is the smaller. Clause 12.5.3: for Category I or II goods the horizontal spacing shall not exceed 3.75 m and the product of horizontal and vertical spacing shall not exceed 9.8 m2; for Category III or IV goods the horizontal spacing shall not exceed 1.9 m and the product shall not exceed 4.9 m2.
Can in-rack sprinklers be fed from the same control valve set as the ceiling sprinklers?
Clause 7.2.3.1 (TS p.40 / EN p.37): where more than 50 intermediate level sprinklers are installed in racks, they shall not be fed from the same control valve set as the roof or ceiling sprinklers. There is no such prohibition at 50 or fewer.
Can pre-calculated pipe sizing be used on a system with in-rack sprinklers?
No. Clause 13.1 (TS p.85 / EN p.82) requires the fully calculated method to be used at all times for arrangements with intermediate level HHS sprinklers and for gridded or looped arrangements. Clause 7.2.3.4 repeats that in-rack sprinklers and their associated ceiling sprinklers shall always be fully calculated.
References
- TS EN 12845+A2:2026 Clause 6.3.2 - Storage configuration ST1-ST6 (TS p.36 / EN p.33)
- TS EN 12845+A2:2026 Table 2 and footnotes a-h (TS p.37 / EN p.34)
- TS EN 12845+A2:2026 Clauses 7.2.2.2, 7.2.2.3 (TS p.39-40 / EN p.36-37)
- TS EN 12845+A2:2026 Clauses 7.2.3.1, 7.2.3.2, 7.2.3.3, 7.2.3.4 (TS p.40 / EN p.37)
- TS EN 12845+A2:2026 Table 5 (TS p.42 / EN p.39)
- TS EN 12845+A2:2026 Clause 12.3 (TS p.75 / EN p.72)
- TS EN 12845+A2:2026 Clauses 12.5.1-12.5.6 and Table 21 (TS p.81-85 / EN p.78-82)
- TS EN 12845+A2:2026 Clause 13.1 (TS p.85 / EN p.82)
- TS EN 12845+A2:2026 Clause 13.4.4 (TS p.105 / EN p.102)
- TS EN 12845+A2:2026 Table 37a (TS p.107 / EN p.104)
- TS EN 12845+A2:2026 Clause 14.5.1, Table 38 (TS p.109 / EN p.106)
- TS EN 12845+A2:2026 Clause 14.7 (TS p.109 / EN p.106)
- TS EN 12845+A2:2026 Clause 20.3.2.2 (TS p.123 / EN p.120)
- TS EN 12845+A2:2026 Clause G.3.4 (TS p.149 / EN p.146), Table G.6 (TS p.153 / EN p.150), Clauses G.8.2-G.8.3 (TS p.154 / EN p.151)
- TS EN 12845+A2:2026 Annex P (TS p.167 / EN p.164)
- TS EN 12845-2:2024 Introduction (EN p.4), Clauses 6.6.1 and 6.6.2.1.1 (EN p.36 et seq.)
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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.