C categories or A–D classes — what should go in the specification?

The C category under PN-EN ISO 12944-2. The A–D letter from PN-EN 13964 tells you which environment the supplier declares the set for, but not what protects the structure — the same letter can cover both a lacquered steel grid and a stainless-steel one. The C category describes the aggressiveness of the environment, and system manufacturers assign the product to it based on testing (Ecophon: NORDTEST NT MAT 003). If the client requires a letter, give both and attach the data sheet.

Is ordinary stainless steel enough at a swimming pool?

No. Grades without molybdenum, such as 1.4301, crack under stress corrosion cracking in a chlorine atmosphere — without visible rust and without warning. Load-bearing elements in swimming pool halls are made from high-alloy grades (1.4529, 1.4547, 1.4565). Ordinary stainless steel can stay where nothing hangs from it above the water and where it can be cleaned regularly.

Why isn't there a C2 category in the catalogues?

Because system manufacturers split their range where the difference is real. Ecophon classifies the Connect grid into C1, C3 and C4 — for interiors that fall into C2 under the standard (unheated halls, warehouses with periodic condensation), a C3-rated product is used instead. It costs little and removes any debate at handover.

Is a moisture-resistant panel enough in a humid room?

No, because the panel and the grid are two independent decisions. A tile rated for 95% relative humidity hung on a standard galvanised grid gives a ceiling with the service life of that grid — the weakest element sets the durability of the whole. The whole set is chosen together: panel, profiles, hangers and fittings.

How much does a higher category cost?

Moving up one category at the costing stage is usually a few percent of the ceiling's value, because the difference lies in the profile coating and the fitting material, not in the surface area itself. Replacing a ceiling in an operating building means material cost, labour and taking the room out of use — plus a risk that can't be captured in a cost estimate.

For contractorsFor designers

Corrosion resistance classes for the ceiling structure vs. room type

Which corrosivity category C1–C4 applies in an office, kitchen, changing room and swimming pool hall — and how the grid, hangers and fittings must be protected accordingly.

Opublikowano 23 August 2026

For designers and specifiers: choosing the corrosion protection of the suspended-ceiling structure to match room conditions.

The lifespan of a suspended ceiling is decided not by the visible panel but by the structure you never see. A ceiling tile in a humid room will, at worst, change dimension or shade — a corroded hanger, rod or wall angle means the ceiling stops holding. That's why anti-corrosion protection for the grid and fittings is chosen to match the room, not the budget.

We select them by the corrosivity category of the environment under PN-EN ISO 12944-2: from C1 for dry, ventilated interiors to C4 for wet, heavily polluted environments. In the systems we work with (Ecophon acoustic ceilings), the Connect grid is classified in exactly these categories — C1, C3 and C4 — and the assignment is confirmed by testing to NORDTEST NT MAT 003, which is stricter than the requirements of ISO 12944-2 itself. A C category is therefore not a goodwill declaration but the result of testing a specific profile.

Below are two tables we use in quotes and coordination meetings: the first explains categories C1–C4, the second starts from where the decision really begins — the room type. After that: why we don't specify by classes A–D, a ready-made paragraph to paste into a specification, and the most important point of all — why "stainless steel" is not a sufficient answer in swimming pool halls.

Four categories: C1, C2, C3 and C4

Corrosivity categories under PN-EN ISO 12944-2 — environment, typical rooms and the required structural protection
Category	Environment	Typical rooms	Structure and fittings
C1	Dry, ventilated, heated interiors without contaminants that accelerate corrosion.	Offices, classrooms, consulting rooms, shops, hotels, corridors and lobbies in heated buildings.	Standard galvanised grid and galvanised fittings — the baseline level that every system meets. There's no reason to pay extra.
C2	Unheated interiors with periodic condensation; atmosphere with light pollution.	Unheated halls and warehouses, seasonal buildings, buffer spaces.	In system catalogues, C2 usually doesn't appear as a separate item (Ecophon offers C1, C3 and C4) — for such interiors a C3-rated product is used instead.
C3	Humid interiors with low air pollution, subject to regular cleaning and periodic condensation.	Catering kitchens, dishwashing rooms, laundries, changing rooms with showers, food processing, dairies.	A grid and fittings with increased resistance — coatings and materials chosen for washing; in the system catalogue this is an item with a declared C3 category, not a "similar" substitute.
C4	Wet interiors with high pollution — constant moisture, aerosols, disinfectants, chlorides.	Swimming pool halls, wet spa zones, wash bays, chemical plants, coastal buildings, garages with salted water run-off.	The highest resistance available in the system: aluminium or stainless steel, with fittings in the same material. In swimming pool halls this is still not enough for load-bearing elements — see the box below.

Przewiń w poziomie, aby zobaczyć wszystkie kolumny

Room type — required category

Room type and the required corrosivity category of the suspended-ceiling structure
Room	Category	Grid and fittings material	What to remember
Office, classroom, consulting room, hotel room	C1	Galvanised steel, standard fittings	Upgrading the category here is throwing money away — the budget is better spent on acoustics.
Corridor, lobby, stairwell in a heated building	C1	Galvanised steel	Exception: the entrance zone, where road salt gets tracked in during winter — C3 is worth adopting there.
Sales floor, shopping mall	C1	Galvanised steel	Above the catering zone in a food court, conditions are already like a kitchen — a separate category applies to that zone.
Heated sports hall, gymnasium	C1	Galvanised steel, reinforced structure	A different class decides here — impact resistance 1A/2A/3A under PN-EN 13964, not corrosion.
Unheated hall, warehouse, production hall without wet processes	C2 → C3	A product with a declared C3 category (C2 is usually not a separate catalogue item)	It's not average humidity but nighttime cooling that settles the matter: warm air condenses on the cold grid.
Catering kitchen, dishwashing room, laundry	C3	Grid and fittings in the declared C3 category	Above the dishwasher and the extractor hood, conditions can already resemble C4. Factor in cleaning with alkaline agents.
Changing room with showers, bathhouse, cubicle area	C3	Grid in category C3, fittings of the same class	If effective ventilation is missing or switched off overnight, adopt C4.
Sauna, wet spa zone, steam bath	C4	Aluminium or stainless steel	Condensation is the rule here, not the exception; oils and disinfectants add to it.
Swimming pool hall with chlorinated water	C4	Load-bearing elements in high-alloy stainless steel (1.4529, 1.4547, 1.4565)	The hardest case in the whole table — see the box below. Grades 1.4301 and 1.4401 are not permitted under load.
Car wash, vehicle wash hall	C4	Aluminium or stainless steel, no galvanised steel parts	Aerosol with detergents and salt from wheel arches settles on everything, including above the lights.
Food processing, dairy, abattoir, brewery	C3 / C4	Stainless steel, coatings approved for food contact	The pressure-washing and disinfection regime can be harsher than the humidity itself — that's what tips the balance towards C4.
Chemical plant, electroplating shop, battery room	C4	A bespoke solution, confirmed by the manufacturer	State the specific compounds and their concentrations in the documentation — without that no one can confirm the selection.
Underground garage, multi-storey car park	C3 / C4	Aluminium or stainless steel above traffic lanes	In winter, chlorides from road salt in the water aerosol — an environment closer to a swimming pool than a warehouse.
Exterior soffit, covered walkway, coastal building	C4	Aluminium with a UV-resistant coating, stainless-steel fittings	Even kilometres from the sea, salt aerosol reaches everywhere; galvanised fittings are out of the running.

Przewiń w poziomie, aby zobaczyć wszystkie kolumny

Uwaga

Swimming pool halls: “stainless steel” isn't enough

On 9 May 1985, in Uster, Switzerland, the suspended ceiling of a swimming pool hall came away and fell into the pool, killing twelve people. What failed was not the cladding but the suspension: rods and stirrups in 1.4301 (V2A) stainless steel — a grade without molybdenum. The mechanism is called stress corrosion cracking: chlorine compounds evaporate from the water, condense on the elements above the pool, dry out and concentrate, and the cycle repeats for years. The component looks clean on the outside — the cracks run inside the material and are invisible from floor level. Rust spots found earlier on the stirrups had been mistaken for dirt.

That's why in swimming pool halls, category C4 alone doesn't settle the matter: for load-bearing elements and everything that hangs above the water — ceilings, wall panels, light fittings, ventilation components, signage — high-alloy grades resistant to this phenomenon are used: 1.4529, 1.4547 and 1.4565. The common grades 1.4301 and 1.4401 are suitable for elements that carry no load and can be cleaned regularly. On top of that, three conditions are easy to forget in a design: inspection access to the suspension, an inspection plan recorded in the as-built documentation, and ventilation that prevents vapour from condensing above the water surface.

Why we don't specify by classes A–D

Ceiling documentation also references environmental-condition classes A, B, C and D from PN-EN 13964: A means humidity up to 70% and temperature up to 25 °C, B up to 90% and 30 °C, C above 90% with condensation risk, D “conditions more severe than the above”. The problem is practical, not normative: the letter describes the ENVIRONMENT the supplier declares the set for, but says nothing about WHAT protects the structure or how that was verified.

The effect shows up in tenders: the same letter can hide a lacquered steel grid just as easily as a stainless-steel one — and in a wet interior the difference in service life is measured in years. The C category under PN-EN ISO 12944-2 is more robust here, because it describes the aggressiveness of the environment to which the manufacturer assigns the product based on testing (at Ecophon, NORDTEST NT MAT 003, stricter than ISO 12944-2 alone). That's why we write the C category into our specifications, and when a client requires a letter from PN-EN 13964, we give both and ask for a technical data sheet showing exactly what protects the profile.

Seven rules that save you from complaints

The room sets the category, not the price list
The designer states the conditions: temperature, relative humidity, condensation risk, aggressive agents and the cleaning regime. Only then is the C category chosen. Missing conditions in the documentation is an invitation to default to C1.
The category applies to the whole set, not just the panel
Hangers, rods, main and cross profiles, wall angles, screws, rivets, anchors and ceiling suspension points — the weakest element sets the durability of the whole. In Uster, it was the suspension that failed, not the ceiling.
Don't mix metals in a humid interior
Aluminium paired with steel in the presence of condensate forms a galvanic couple and corrodes faster than humidity alone would suggest. Either use a single material throughout the set, or insert separating spacers.
Condensation matters, not average humidity
What decides it is surface temperature relative to the dew point. An unheated hall with warm, humid air in the evening can be more aggressive than a constantly humid but warm changing room — and deserves a higher category.
Choose the cleaning regime together with the category
Pressure washing and disinfection can be harsher than the air itself, and manufacturers explicitly tie the permitted cleaning method to the grid's corrosion category. In higher categories, deposits must be rinsed off, and load-bearing elements must remain accessible for inspection.
Cut to size in the factory, not on site
Every cut and drilled hole exposes an uncoated edge. In C1, zinc still provides cathodic protection there; in C3 and C4, improvising on site invalidates the manufacturer's declaration.
Demand a data sheet, not assurances
A data sheet with the declared corrosion category of the profile and fittings, plus the set's declaration of performance. If the supplier only gives a letter A–D, ask what's behind it: the material, the coating and the test method.

Ready to paste into a specification

A paragraph that closes the topic at the tender stage — just fill in the fields and enter the category from the table above.

The suspended ceiling, together with its supporting structure and fittings, forms a set under PN-EN 13964. Required corrosivity category under PN-EN ISO 12944-2: ____ (C1 / C3 / C4).

Room conditions: temperature ____ °C, relative humidity ____ %, condensation risk: yes / no, presence of chlorine or disinfectants: yes / no, cleaning method: ____ .

The required category applies to all elements of the set: hangers, rods, main and cross profiles, wall angles, connectors and fixing elements to the soffit.

In swimming pool halls, load-bearing elements must be made of stainless steel resistant to stress corrosion cracking (e.g. 1.4529, 1.4547, 1.4565); grades 1.4301 and 1.4401 are not permitted for load-bearing elements.

The supplier provides data sheets for the profiles and fittings with the declared corrosion category and the method used to confirm it, plus the set's declaration of performance. Load-bearing elements remain accessible for inspection.

Najczęściej zadawane pytania

C categories or A–D classes — what should go in the specification?
The C category under PN-EN ISO 12944-2. The A–D letter from PN-EN 13964 tells you which environment the supplier declares the set for, but not what protects the structure — the same letter can cover both a lacquered steel grid and a stainless-steel one. The C category describes the aggressiveness of the environment, and system manufacturers assign the product to it based on testing (Ecophon: NORDTEST NT MAT 003). If the client requires a letter, give both and attach the data sheet.
Is ordinary stainless steel enough at a swimming pool?
No. Grades without molybdenum, such as 1.4301, crack under stress corrosion cracking in a chlorine atmosphere — without visible rust and without warning. Load-bearing elements in swimming pool halls are made from high-alloy grades (1.4529, 1.4547, 1.4565). Ordinary stainless steel can stay where nothing hangs from it above the water and where it can be cleaned regularly.
Why isn't there a C2 category in the catalogues?
Because system manufacturers split their range where the difference is real. Ecophon classifies the Connect grid into C1, C3 and C4 — for interiors that fall into C2 under the standard (unheated halls, warehouses with periodic condensation), a C3-rated product is used instead. It costs little and removes any debate at handover.
Is a moisture-resistant panel enough in a humid room?
No, because the panel and the grid are two independent decisions. A tile rated for 95% relative humidity hung on a standard galvanised grid gives a ceiling with the service life of that grid — the weakest element sets the durability of the whole. The whole set is chosen together: panel, profiles, hangers and fittings.
How much does a higher category cost?
Moving up one category at the costing stage is usually a few percent of the ceiling's value, because the difference lies in the profile coating and the fitting material, not in the surface area itself. Replacing a ceiling in an operating building means material cost, labour and taking the room out of use — plus a risk that can't be captured in a cost estimate.

Sources

Wszystkie wpisy Więcej w tej kategorii