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

> Cleanroom construction means building rooms whose air is held to an ISO 14644-1 class, a limit on airborne particles at stated sizes. The class is a performance target, not a building specification: the HVAC engineer sets airflow and filtration to meet it, and the room must supply sealed, non-shedding, cleanable surfaces and airtight junctions so pressure can be held.

## 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

| Element | What the class drives | Who decides | What the building must provide |
| --- | --- | --- | --- |
| Airflow and air changes | Dilution and removal of particles | HVAC engineer | Space for ducts, AHUs and return paths |
| Filtration | Terminal filter grade and coverage | HVAC engineer | A ceiling that carries and seals filter housings |
| Pressure cascade | Direction of air between rooms | HVAC engineer with the user | Airtight rooms, airlocks, sealed penetrations |
| Surfaces and finishes | How few particles the room sheds and traps | Designer with the user's QA | Non-shedding, non-porous, coved, cleanable |
| Doors and pass boxes | Transfer without breaking the cascade | Designer with the user | Flush, sealed doors; interlocks where specified |
| Qualification | Evidence the room meets its class | User's QA, tested to ISO 14644-1 | Records, test access, a clean-build process |

## 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](/glossary/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](/materials/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](/guides/pharma-facility-construction-guide)
and on the [pharma and life sciences](/industries/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.

## Frequently asked questions

### What does an ISO class actually measure in a cleanroom?

ISO 14644-1 classifies air cleanliness by the concentration of airborne particles per cubic metre at one or more threshold sizes between 0.1 and 5 micrometres, measured with a particle counter at defined locations. A lower class number means cleaner air. It does not measure microbes, chemicals or the room's construction; those are dealt with by other standards and by the user's quality system.

### Is an ISO class the same as a GMP grade?

No. ISO 14644-1 is a particle classification used across industries. GMP frameworks such as EU GMP Annex 1 and India's revised Schedule M set grades for regulated pharmaceutical manufacture that also cover microbial limits, monitoring and the state of the room in operation. Which grade each room needs is set by the manufacturer's quality team against the regulator's requirements, not by the building contractor.

### How many air changes does a cleanroom need?

There is no figure that can be read off the class. Airflow and filtration are chosen by the HVAC engineer from the class, the process, the heat load, the number of people and the recovery time the user wants, and then proved by testing. A room is classified on measured particle counts, so a number of air changes on a drawing proves nothing on its own.

### Can a cleanroom be built with ordinary drywall?

Some lower-grade controlled rooms are built from boarded partitions with a sealed, cleanable coating, but the joints, corners and penetrations are hard to keep sealed and they crack as the building moves. Prefabricated metal-faced panel systems with sealed joints, flush doors and coved junctions are more common where the class or the cleaning regime is demanding. The designer chooses against the class and the disinfectants used.

### What is a pressure cascade?

It is the arrangement of room pressures so that air always moves from the cleaner room to the less clean one, through door gaps and airlocks, carrying particles away from the critical area. The pressure differences are set by the HVAC engineer and monitored in operation. They only hold if the rooms are airtight: an unsealed light fitting or cable entry can defeat the design.

### Who signs off that a cleanroom meets its class?

Classification is demonstrated by testing to ISO 14644-1, carried out by a competent tester with calibrated instruments, in the occupancy state the specification names. For regulated manufacture the user's quality function then qualifies the facility under its GMP system, and the regulator inspects. The contractor's role is to build to the design and hand over the records that qualification depends on.

## Sources

- [ISO 14644-1](https://www.iso.org/standards.html) — Cleanrooms and associated controlled environments - classification of air cleanliness by particle concentration
- [ISO 14644-4](https://www.iso.org/standards.html) — Cleanrooms and associated controlled environments - design, construction and start-up
- [EN 13501-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Fire classification of construction products - reaction to fire
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/) — Fire and life safety

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Source: https://hagerstone.com/blog/cleanroom-classes-iso-14644-what-they-mean-for-construction