This guide covers the full path of a cleanroom investment: from the user requirement specification (URS), through HVAC design and construction, to IQ/OQ/PQ qualification. It is written for plant engineers and investors who need to understand what they are buying before they sign — including the air change rates ISO 7 requires, how validation works under EN ISO 14644-1 and EU GMP Annex 1 (2022 revision), and what construction and annual operation actually cost.

This is a technical guide. If you are looking for a contractor rather than theory, see how turnkey cleanroom construction works at Clima Line: scope of work, ISO 5–8 classes, timelines and cost ranges.

1. What a cleanroom is and when you need one

A cleanroom is a space with controlled concentration of airborne particles, in which temperature, humidity and pressure differentials are also held within defined limits. The definition matters because it rules out the common shortcut: a well-filtered ventilation system is not a cleanroom. Without a pressure cascade and validated air change rates, filtration alone does not produce a controlled environment.

You need one when your process is measurably damaged by contamination — pharmaceutical and medical device manufacturing, sterile filling, optics, microelectronics, sensor assembly, automotive glass lamination — or when your customer’s specification demands it regardless of your own view.

2. ISO 14644-1 classes and how they map to GMP

ISO 14644-1 classifies by particle concentration. ISO 7 permits a maximum of 352,000 particles ≥0.5 µm per m³, along with 83,200 particles ≥1 µm and 2,930 particles ≥5 µm. ISO 8 permits ten times more, ISO 5 ten times fewer.

GMP adds two things ISO does not: microbiological limits, and a formal distinction between at rest (installation complete and running, no personnel) and in operation (full production with staff). GMP grade A corresponds to ISO 5 in both states; grade B is ISO 5 at rest and ISO 7 in operation; grade C is ISO 7 at rest and ISO 8 in operation; grade D is ISO 8 at rest with no defined in-operation limit.

The practical consequence: a room designed tightly for the at-rest state falls out of class the moment four operators walk in. Design must target the in-operation state.

3. What a URS is and why it comes before design

The User Requirement Specification defines what the room must achieve, in measurable terms, before anyone draws it. It states the required class per zone, temperature and humidity tolerances, pressure regime, personnel and material flows, equipment to be installed, and the regulatory framework the room must satisfy.

Writing it first is not bureaucracy. The URS is the document against which qualification is later performed — if it does not exist, there is no objective definition of what “working correctly” means, and acceptance becomes a negotiation. Most failed cleanroom investments we are called to repair had no URS, or had one written after the design was frozen.

4. Construction stages — from concept to handover

Weeks 1–2: process analysis and URS. Identifying which operations genuinely require a clean zone, what tolerances the process imposes, and how people and materials will move.

Weeks 3–6: process and detailed design. Heat and moisture balance, air change rates, pressure cascade with airlocks, selection of air handling units, chiller and filtration, controls design. The modular-versus-masonry decision belongs here.

Weeks 7–12: enclosure and installations. Panels, resin floors and hermetic doors in parallel with ductwork, chilled water piping and control wiring.

Weeks 13–16: commissioning, balancing and qualification. Unit start-up, airflow balancing, cascade setting, then IQ/OQ/PQ.

For ISO 7 at 200–500 m² the whole path typically runs 12–20 weeks from detailed design approval. Modular construction shortens it by 4–8 weeks against masonry.

5. Designing the HVAC system for ISO 7

HVAC accounts for 50–60% of a cleanroom budget and effectively determines the qualification result. The core parameters:

• Air change rate — for ISO 7, typically 30–60 ACH. The figure follows from particle generation in the room, which depends on headcount and process, not from a table.
• Pressure cascade — typically 10–15 Pa between adjacent classes, maintained by airflow difference and monitored continuously.
• Airlocks with interlocks — personnel and material, with doors mechanically or electrically prevented from opening simultaneously.
• Temperature and humidity with reserve — sized for the hottest week, not the average, and with dehumidification where the process demands it.
• Recovery time — how quickly the room returns to class after a disturbance; a qualification parameter in its own right.

6. Filtration and integrity testing

ISO 7 requires multi-stage filtration ending in terminal HEPA filters — H13 (99.95% at MPPS) or H14 (99.995%). The decisive detail is where the HEPA sits: mounted terminally at the supply point, it can be integrity-tested in situ by the DOP/PAO method. Mounted inside the air handling unit, it cannot — and every duct joint downstream becomes an unverifiable contamination path. This single decision separates rooms that pass qualification from rooms that argue about it.

Integrity testing is repeated annually. Filter replacement is driven by pressure drop, typically at a 50–100% rise over the initial value, which in practice means every 2–4 years.

7. Cleanroom construction materials

Standard build-up: sandwich panels with PIR or PUR core for walls and ceiling, seamless resin flooring coved up the wall to eliminate dust-trapping corners, hermetic doors with drop seals, and windows mounted flush with the wall face. Every joint is sealed; every horizontal surface is a cleaning liability, which is why cable trays and pipework run above the ceiling or in technical corridors, never exposed in the clean zone.

8. Modular or masonry?

Modular is faster by 4–8 weeks, easier to modify later, and can be dismantled and relocated — which matters if the building is leased. Masonry is cheaper per square metre in the shell, more robust against mechanical damage, and better suited to permanent installations in owned premises. For most industrial ISO 7 applications modular wins on total cost once the shortened build time is priced in.

9. IQ/OQ/PQ qualification

IQ (Installation Qualification) verifies that what was installed matches the design: equipment, materials, documentation, calibration certificates.

OQ (Operational Qualification) verifies that the installation performs as specified with no product present: airflow volumes and velocities, pressure differentials, particle counts at rest, filter integrity, recovery time, temperature and humidity stability.

PQ (Performance Qualification) verifies performance under real production conditions, with staff and process running — particle counts in operation, and for GMP applications microbiological monitoring.

Requalification under ISO 14644-2:2015 is risk-based rather than fixed-interval; in practice ISO 5 is requalified every 6 months, ISO 7 and ISO 8 every 12.

10. Construction and operating costs

For ISO 7 in Polish conditions, construction runs roughly 3,500–8,000 PLN/m² (about 800–1,900 EUR/m²), split approximately into HVAC at 2,000–5,000 PLN/m², enclosure at 800–2,000 PLN/m², and the remainder for automation, validation and utilities. Higher classes rise steeply: ISO 5 typically 7,000–12,000 PLN/m².

Operating cost is dominated by air handling. At 30–60 ACH the units run continuously, so every unnecessary air change is a permanent charge. Over-specifying by one class raises investment by 40–80% and annual running cost by 150–300%. Add the recurring cost of requalification and filter replacement, and the case for sizing from the process rather than “with a margin” becomes financial rather than technical.

11. The most common mistakes

• air change rate calculated for at rest, so the room fails in operation,
• HEPA filters in the air handling unit instead of terminally — no in-situ integrity testing,
• pressure cascade that collapses whenever an airlock door opens,
• no cooling reserve, so temperature tolerance is lost in a heatwave,
• thermal bridges producing condensation and microbial growth on wall surfaces,
• monitoring without continuous recording — no evidence of compliance between qualifications.

12. Case study: 400 m² ISO 7 for automotive

Total airflow above 100,000 m³/h, absorption dehumidifiers rated 18,000 m³/h, an 800 kW chilled water plant with capacity reserve, final H14 filtration, minimum 15 Pa overpressure. Full description: case study of the 400 m² ISO 7 cleanroom. Process-specific requirements per automotive operation: cleanrooms for the automotive industry.

13. Why Clima Line

We have delivered cleanrooms since 2013 — five above 1,000 m² of combined area and around ten retrofits of operating facilities. The technology side is led by Marcin Sompoliński, PhD Eng., co-owner of the company. We grew out of industrial refrigeration and process ventilation, so the air design is done in-house rather than subcontracted, which is why we take responsibility for the qualification result and not only for the installation. Documentation can be issued in English for international audits.

14. Frequently asked questions

Which ISO class corresponds to GMP grade A?

Grade A corresponds to ISO 5 in both the at-rest and in-operation states — the most demanding requirement in the pharmaceutical classification, typically applied to aseptic filling zones under unidirectional airflow.

How long does an ISO 7 cleanroom take from design to handover?

Typically 12–20 weeks for 200–500 m² from detailed design approval, plus qualification. Modular construction shortens this by 4–8 weeks against masonry.

Does validation have to be repeated annually?

ISO 14644-2:2015 moved from fixed intervals to a risk-based monitoring plan. In practice ISO 5 is requalified every 6 months and ISO 7 and ISO 8 every 12. GMP grades A and B follow the 6-month cycle.

Which is more expensive — modular or masonry?

Masonry is usually cheaper per square metre in the shell alone, but modular typically wins on total cost once the 4–8 week shorter build and easier future modification are priced in.

Does an ISO 7 cleanroom need unidirectional (laminar) airflow?

Generally no. Unidirectional flow is characteristic of ISO 5 and GMP grade A. ISO 7 is normally achieved with turbulent mixed flow at an appropriate air change rate, with laminar modules used only above specific critical workstations.

How much energy does a 200 m² ISO 7 cleanroom use?

Consumption is dominated by continuous air handling at 30–60 ACH plus dehumidification where the process requires it. The single largest lever is the air change rate — which is why sizing it from the process rather than from a table is a financial decision, not just a technical one.

Can an existing ISO 8 cleanroom be upgraded to ISO 7?

Often yes. It usually requires increasing the air change rate, adding a filtration stage and reworking the pressure cascade — and sometimes uprating the cooling plant. We start with measurements to establish what the existing infrastructure can carry.

What is EU GMP Annex 1 and does it apply to me?

Annex 1 governs the manufacture of sterile medicinal products in the EU. The 2022 revision introduced the Contamination Control Strategy as a superior document, made smoke studies a standard part of qualification, and reinforced the preference for RABS and isolator technology. It applies if you manufacture sterile products for the EU market. Details: pharmaceutical cleanrooms (GMP).

What auxiliary installations does a cleanroom need beyond HVAC?

Sealed electrical installations with flush ceiling luminaires, a BMS controlling units and dampers and holding the 10–15 Pa cascade, and a separate RMS recording temperature, humidity, differential pressure and particle counts with an audit trail. Separating BMS from RMS is a practical requirement: an auditor will not accept evidence from the system that also sets the parameters. Details: HVAC automation and BMS.

15. Planning a cleanroom project?

Send us your process description and hall layout — we will prepare a concept with air balance, proposed class and a quotation broken down into enclosure, HVAC, automation and validation. Call +48 32 450 56 66 or write to biuro@clima-line.pl.

Related pages: cleanroom construction · pharmaceutical cleanrooms GMP · controlled environments for defence · industrial HVAC service.