Cleanroom Classes and ISO 14644: What They Mean for the Building

A cleanroom class is a limit, not a product

Cleanrooms are often bought as if the class were a product: "we need an ISO 7 room." The tender goes out with a class and a floor area, and the contractor is left to decide what that means for walls, ceilings, doors and finishes.

That is the misconception worth correcting first. An ISO 14644-1 class is a limit on airborne particles, measured in a finished room. It says nothing about how to build the room. The class is reached by three things working together: the air system that dilutes and filters particles, the room that stops them being generated or let in, and the people and process inside it.

For a plant head or CFO, getting this wrong does not show up until the end. Classification testing fails, or a room holds its class empty but not in operation, and the fix is rarely cheap: resealing junctions, replacing a shedding ceiling, rebalancing air, or moving a door. Each of those delays the qualification that production is waiting for.

How ISO 14644-1 classifies a room

ISO 14644-1, Classification of Air Cleanliness by Particle Concentration, sets classes from ISO Class 1, the cleanest, to ISO Class 9. Each class is a maximum number of particles per cubic metre of air at or above stated particle sizes, within the range 0.1 to 5 micrometres. The class number works as a power of ten, so each whole step up the scale allows roughly ten times more particles. The limit values themselves are tabulated in the standard; this page explains the method rather than reproducing them.

Three points matter for the building:

• The occupancy state must be named. The standard defines a room as-built (finished, services running, no equipment or people), at-rest (equipment installed, no people) and operational. A room that meets its class as-built may not meet it operational, because people and machines generate particles.
• Classification is by measurement. A particle counter samples at locations set out by the standard. Drawings, air change figures and product data sheets are inputs, not proof.
• It covers particles only. Microbial contamination, which matters most in sterile pharmaceutical manufacture, is handled by GMP frameworks and the user's monitoring programme.

What the class drives, and who decides each part

The HVAC sets the number of air changes, not the class table

The airflow a cleanroom needs is not read from the class. The HVAC engineer derives it from the class, the process, internal heat, the number of people and how quickly the room must recover after a disturbance, and then commissioning proves it. Air changes per hour explains why the figure is a design output for these rooms rather than a rule of thumb.

What the HVAC design asks of the building is physical. Terminal filters sit in the ceiling, so the ceiling grid must carry their weight and seal around each housing. Return air is often drawn at low level, which puts return risers inside or behind the wall panels and fixes their positions early. Large air volumes need plant space and plenum depth above the rooms. A layout that is frozen before the HVAC engineer has placed filters and returns usually gets redrawn.

A pressure cascade needs an airtight room

A pressure cascade keeps air moving from cleaner rooms to less clean ones, so particles are carried away from the critical area through door gaps and airlocks rather than into it. The engineer sets the pressure differences; the building decides whether they can be held.

Air finds every gap. The usual leaks are light fittings not sealed into the ceiling, cable and pipe penetrations left open behind panels, panel joints where sealant was skipped at a corner, and door frames that were not sealed to the wall. A room that leaks needs more air to hold its pressure, and sometimes cannot hold it at all. Sealing is cheapest during construction, before the ceiling closes, and should be inspected as a stage, not left to the end.

Finishes, panels, doors and pass boxes

Coved junctions. Floor-to-wall and wall-to-ceiling junctions are normally coved rather than square, so there is no corner to collect dust or resist a mop. Ledges, exposed fixings and horizontal surfaces are avoided for the same reason.

Non-shedding, sealed surfaces. Every finish must be smooth, non-porous and compatible with the cleaning and disinfecting agents the user will actually use. A coating that softens under a disinfectant fails in service, not at handover. Floors are commonly resin systems with integral coved skirting; PU concrete flooring suits wet and washdown-heavy areas.

Wall and ceiling panels. Prefabricated metal-faced panel systems with sealed joints are widely used because they give flush faces and repeatable junctions. Ceilings may be walkable, allowing maintenance from above, or non-walkable and serviced from below; that choice changes how filters and lights are maintained. Panel cores vary in fire behaviour, so the core's reaction-to-fire class to EN 13501-1 should be stated, and what the building requires is decided by the fire consultant under NBC 2016, Part 4.

Doors and pass boxes. Doors are flush, with flush-glazed vision panels and seals, and are often interlocked at airlocks so both cannot open together. Pass boxes transfer materials between rooms without people moving; whether a static or a ventilated pass box is used is set by the user and the HVAC engineer.

Qualification starts on day one of construction

ISO 14644-4 covers the design, construction and start-up of cleanrooms, including the checklists that link requirements to design and construction. Classification testing to ISO 14644-1 comes at the end, but it depends on decisions made throughout: a clean-build protocol once the room is closed, the order in which trades finish, sealed services, and records of materials and inspections. For regulated manufacture, the user's quality team qualifies the facility under its GMP system, and frameworks such as EU GMP Annex 1 and India's revised Schedule M to the Drugs Rules set the grades and expectations. Which grade applies to each room is the user's and regulator's decision. The wider plant picture is covered in the pharma facility construction guide and on the pharma and life sciences page.

Common mistakes

• Tendering a class instead of a specification. "ISO 7" with no occupancy state, finishes schedule or HVAC basis invites as many interpretations as bidders.
• Fixing the layout before the HVAC engineer has placed filters, returns and airlocks.
• Sealing left to the end, when penetrations are already behind closed panels.
• Finishes chosen without the disinfectant list, so coatings degrade within months.
• No clean-build protocol, so dust from late trades sits in the plenum and shows up at testing.
• Confusing an ISO class with a GMP grade and assuming one answers the other.

What to ask your designer and contractor

• Which ISO 14644-1 class does each room need, and in which occupancy state?
• Who is setting the air changes, filtration and pressure cascade, and on what basis?
• What is the panel system, its core's fire class and the joint sealing detail?
• Which cleaning and disinfecting agents were the finishes checked against?
• How will sealing be inspected before ceilings close?
• What records will be handed over to support qualification?

Standards referenced

Air cleanliness classification by particle concentration in ISO 14644-1; cleanroom design, construction and start-up in ISO 14644-4; reaction-to-fire classification of panel products in EN 13501-1; fire and life safety in NBC 2016, Part 4. GMP grades under EU GMP Annex 1 and Schedule M are mentioned as the regulatory framework only. The class, GMP grade, airflow, pressure regime and finishes for a specific facility must be set by the user's quality team, the HVAC engineer and the project consultants, and confirmed by testing; nothing on this page replaces that design.