What Is a Cleanroom? ISO Classes and Containment Needs

Every cleanroom carries an ISO classification from 1 to 9 that sets its particle limit and drives every design and monitoring choice around it. Any renovation or expansion happening nearby becomes its own project, because the classification only holds while the environment around it does.

At STARC, we've spent years on the containment side of that equation, protecting sterile spaces during buildouts and phased work across life sciences and biotech.

If you're a facility engineer or GC planning work near a classified space, this guide covers how ISO classification works, what separates each class, and what containment must withstand when construction starts next door.

What Is a Cleanroom?

A cleanroom is a room where airborne particle counts stay under a strict, defined limit. The same control usually extends to temperature and humidity, since particles travel more easily when conditions drift, and to pressure, which keeps outside air from pushing in.

Standard cleaning removes visible dirt from surfaces, while a cleanroom strips particles at the sub-micron level, a scale only a particle counter can detect.

Cleanrooms show up wherever airborne contamination puts a process at risk. Semiconductor manufacturing, sterile drug compounding, cell culture work, medical device assembly, and satellite optics all depend on that particle control.

How Cleanrooms Work

Filtered air drives everything a cleanroom does. Supply air passes through HEPA or ULPA filters before it enters the room, and those filters strip particles down to fractions of a micron before staff or equipment touch that air.

Air change rates set how fast that filtered air replaces the air already inside. A standard office might exchange air a handful of times per hour, while a cleanroom can exchange it dozens or hundreds of times per hour, depending on its classification.

Pressure seals the room against outside contamination. Cleanrooms typically operate at higher pressure than the surrounding spaces, so air pushes outward through doorways and seams, keeping hallway dust from drifting in.

That's the mirror image of the negative-air-pressure approach used to contain construction dust in healthcare renovations, where the goal is keeping contaminated air inside the work zone instead of outside the clean one.

Ceiling-mounted filters carry part of that airflow balance, and sealed wall systems carry the rest. Gowning anterooms round out the picture, giving staff a controlled entry point that protects the pressure the room depends on.

What Is a Cleanroom Classification?

The ISO 14644-1 standard sets the specific particle limits behind each class. ISO 1 allows just 10 particles at 0.1 microns per cubic meter, while ISO 9 allows over 35 million particles at 0.5 microns, a level close to normal room air.

Most industrial and pharmaceutical cleanrooms land between ISO 5 and ISO 8. Anything cleaner than ISO 4 requires airflow and filtration far beyond what most processes need, so those classes stay rare outside nanotechnology and aerospace work.

How ISO 14644-1 Classifies a Cleanroom

ISO 14644-1 assigns a class based on particle counts measured by technicians across multiple sample points in the room, then compares those counts against the maximum allowed for each class at specific particle sizes.

Actual measurements determine the final classification, regardless of the room's design or filter type. A few details of the test itself carry as much weight as the particle count:

• Particle size: ISO 14644-1 tracks particles across six size thresholds from 0.1 to 5 microns. A room can pass at one size and fail at another, so every classification report names which size the technician measured.

• Recertification schedule: Airflow patterns and filter wear shift particle counts over time, so facilities recertify cleanrooms on a set cadence rather than relying on the original build test.

• "At rest" vs "in operation": An empty room classifies cleaner than the same room during active production, so a credible report names which condition the test used. A room that passes empty can still fail once staff and equipment are running.

What Each ISO Class Actually Requires

ISO 3 through ISO 5 need unidirectional airflow. These classes typically rely on laminar flow, where filtered air moves in parallel lines across the ceiling or wall, sweeping particles out before they settle. Fan filter unit coverage often reaches full ceiling coverage in ISO 3 and ISO 4 spaces.

ISO 6 through ISO 8 use turbulent, non-unidirectional airflow. Air enters through ceiling-mounted HEPA filters and mixes throughout the room rather than moving in a single direction. This costs less to build and operate, though it caps out below the particle counts laminar flow can reach.

Hardwall construction dominates below ISO 6. Rigid wall panels hold pressure differentials in a way that softwall or curtain-based rooms struggle to match. Above ISO 6, softwall cleanrooms using suspended curtain systems become a viable, lower-cost option.

Gowning requirements tighten as the class number drops. ISO 8 rooms often permit standard cleanroom garments with minimal procedure.

ISO 5 and cleaner classes typically require full-body coveralls, hoods, and a documented gowning sequence performed in an anteroom or buffer room rather than at the cleanroom's main entry, since one uncontrolled entry can compromise an entire batch.

Room size and equipment heat load both affect how much filtered air a space needs to hold its classification. Staff count plays a role too, which together explains why the air change rates above span such a wide range.

Cleanroom Classes vs. the Old Federal Standard

Older documentation may still reference Federal Standard 209E, the US classification system ISO 14644-1 replaced in 2001.

The two systems use different measurement scales, but a common approximation aligns ISO 5 with the old Class 100 and ISO 7 with Class 10,000, since those pairings fall within the same particle-count range under both standards.

FED-STD-209E carries official cancellation status now, yet legacy equipment specs and older facility drawings still reference it in plenty of active buildings.

Treat any FED-STD-209E class number in older paperwork as an approximation, then confirm the actual required class against current ISO 14644-1 particle limits before designing or certifying a space.

Choosing the Right Classification for a New Space

For a facility team speccing a new cleanroom, the right class is the one the process calls for and survives actual operating conditions.

• Start with what the process actually requires. An overspec on the cleanroom's class drives up construction and operating costs without adding any real benefit. Match the containment level to the actual risk the process presents.

• Check whether a regulatory body already sets the requirement. Industry-specific standards often dictate the required ISO class for pharmaceutical compounding, medical device manufacturing, and semiconductor fabrication, which settles the decision before design begins.

• Confirm the class holds up once the room goes live. Design specs on paper mean little if the room can't hold its rating with a full crew and running equipment inside it.

• Plan for recertification from day one. Build a monitoring and recertification schedule into the facility's operating plan before construction finishes.

Where Cleanroom Standards Intersect With Biotech Construction

Life sciences and biotech facilities apply the same particle-control logic ISO 14644-1 uses to construction happening near active manufacturing, since a single breach can compromise an entire production run rather than just one batch.

A renovation next to a sterile compounding suite or a biologics production line turns airborne particle risk in life sciences and biotech facilities into a contamination event that can shut the line down. That overlap becomes concrete on projects that expand a cleanroom inside an active facility.

Medtronic expanded its cleanroom manufacturing space at a Massachusetts facility, and the construction team needed an airtight barrier between the active build-out and the operating cleanroom next door, since standard drywall took too long to seal without risking contamination during installation.

The contractor used STARC's RealWall™ panels, sealed with foam ceiling gaskets and dual inter-panel seals, to hold that barrier for the length of the project. The panels come down intact for reuse, and the same construction team went on to use STARC's walls on more renovations at the Danvers facility.

Cleanroom-Grade Containment for the Renovation Next Door

A cleanroom's classification only survives when the containment around any nearby construction stays airtight. Which temporary wall does that work turns on the project's air quality and sensitivity profile, and STARC builds that containment for facilities that can't risk contamination during a renovation:

• RealWall™ and LiteBarrier™ both exceed ICRA Class IV/V requirements for healthcare-adjacent construction, including work around airborne infection isolation rooms (AIIRs) during patient-adjacent renovations.

• FireblockWall™ adds a one-hour fire rating for projects where code requires it alongside particle control.

• StackBarrier™ extends that same sealed containment up to 40 feet, which covers cleanroom expansions with tall ceilings or overhead mechanical runs.

Across the whole line, every panel meets ASTM E84 for surface burning characteristics, and each system is built for reuse: RealWall can be reused more than 50 times, and FireblockWall pays for itself in as few as 2 to 4 uses. The same panels that seal one cleanroom expansion can move to the next renovation instead of ending up in a dumpster.

RealWall also ships through Sunbelt Rentals, which gives a short-term cleanroom project a path that skips a full purchase commitment.

Planning a renovation next to a classified space? Request a quote from our experts about the containment level the project actually needs.

Frequently Asked Questions

What is the most common cleanroom classification?

ISO 7 and ISO 8 are the most common cleanroom classifications, since they need only 60-90 and 5-48 air changes per hour, a fraction of the 240+ changes ISO 5 rooms need to sustain laminar airflow.

What is the difference between ISO 5 and ISO 7 cleanrooms?

The difference between ISO 5 and ISO 7 cleanrooms lies in airflow patterns and particle counts. ISO 5 needs unidirectional laminar flow, while ISO 7 uses turbulent airflow that mixes rather than sweeps particles out.

Do all cleanrooms need HEPA filters?

Yes, virtually all classified cleanrooms use HEPA filters, rated to capture 99.97% of particles at 0.3 microns. ISO 4 and cleaner often need ULPA filters instead, rated to 99.999% at 0.12 microns.

How often does a cleanroom need to be recertified?

A cleanroom needs recertification on a schedule set by its class under ISO 14644-2. ISO 5 and cleaner rooms require testing every 6 months, while ISO 6 through ISO 9 rooms follow a 12-month interval.

Does a research lab count as a cleanroom?

No, a general research lab doesn't carry an ISO 14644-1 classification the way a manufacturing cleanroom does, but pharma and biotech facilities that compound sterile products or manufacture cell and gene therapies do hold one, most often ISO 7 or ISO 8.