In cleanroom and controlled environment projects, documentation drives outcomes.
Yet, not all documents serve the same purpose, and confusing them can create costly gaps between what the owner intends and what the facility ultimately delivers.

A common misconception in the cleanroom industry is to treat the User Requirement Specification (URS) as the blueprint for design. While the URS is crucial, it’s not the starting point.
According to ASHRAE Guideline 0 and ASHRAE Standard 202, every project begins with a clearly defined Owner Project Requirements (OPR) document, the foundation of the commissioning process and the reference point for all subsequent design and verification activities.

Let’s break down the difference, and why getting this sequence right is essential for any cleanroom project that aims to perform as intended.

Owner Project Requirements (OPR): The Foundation of Intent

The OPR defines why the project exists and what the owner expects from it — not just in terms of cleanliness or temperature, but also performance, reliability, energy efficiency, budget priorities, and operational flexibility.

It includes:

• Project purpose and functional goals
• Performance and compliance expectations (e.g., GMP, ISO 14644)
• Energy, maintenance, and lifecycle cost targets
• Budget and schedule priorities
• Future scalability or adaptability objectives

In practice, the cleanroom EPC provider or engineering team often leads and facilitates the OPR development.
Owners and end users bring process knowledge and business intent, but they rely on the provider’s technical and regulatory expertise to structure the OPR properly, ensuring it captures measurable, verifiable performance goals.

In short:

The EPC or cleanroom provider leads the OPR process, while the owner reviews and approves it, since it represents the project’s strategic vision.

User Requirement Specification (URS): The Voice of the User

Once the OPR defines why the project exists, the URS defines what the facility must do to meet those objectives.

The URS is developed under the leadership of the user or process owner, because it contains details that extend beyond engineering, touching on operations, production processes, safety, ergonomics, and regulatory compliance.

It covers:

• Cleanliness classifications and zoning (ISO Class levels)
• Environmental conditions (temperature, humidity, pressure differentials)
• Equipment layouts and utilities
• Material and personnel flows
• Gowning, safety, and process-specific protocols

The cleanroom designer or EPC contractor supports this process, validating the URS for technical feasibility, constructability, and regulatory alignment.
But ultimately, it is the user’s responsibility to define what’s required for their product and process integrity.

In short:

The user leads the URS, and the cleanroom provider refines and validates it technically.

The Sequence That Many Miss: OPR ➜ URS ➜ Design ➜ Commissioning

When projects skip the OPR and jump directly to a URS, they risk building a facility that meets specifications — but not the owner’s actual goals.

Without an OPR:

• The URS becomes a wish list rather than a requirements document.
• Design intent drifts, because no strategic benchmark anchors it.
• Energy and lifecycle costs can escalate unnecessarily.
• Commissioning outcomes become harder to verify, since there’s no documented performance baseline.

This confusion is widespread in the cleanroom sector, where “URS-driven design” is often presented as the cornerstone of good practice, but in reality, that’s only half the story.
A properly commissioned cleanroom starts with the OPR, then evolves into the URS, ensuring every technical decision aligns with the owner’s purpose, not just user preference.

Real-World Example: When URS Lacks an OPR

Imagine a process user requests ±2°C temperature control in their URS, believing tighter control equals better performance.
Without an OPR defining why this is necessary, no one questions the intent.
Designers proceed to specify oversized HVAC systems, adding capital cost and operational energy use.

If the OPR had clarified that the process is non-temperature-sensitive (e.g., packaging or assembly work), a ±4°C range might have been perfectly acceptable, saving thousands annually in operating costs while maintaining product quality.

This is a small example of how an unanchored URS can drive overdesign, while a structured OPR brings balance, efficiency, and alignment.

Integrating Both in the Cleanroom Catalyst EPC Framework

At Cleanroom Catalyst, we begin every project with an OPR facilitation workshop, helping owners translate their strategic objectives into measurable performance criteria.
Only after the OPR is established do we move into the URS phase, guided by the process users and validated by our engineering team.

This method ensures:

• Traceability between intent, design, and performance
• Balanced solutions, technically sound, cost-conscious, and compliant
• Smooth commissioning, since performance targets are defined early and verified later

This standards-based approach (aligned with ASHRAE and GMP Annex 15) bridges engineering rigor with process understanding, something that generic “URS-only” approaches often miss.

Conclusion

A User Requirement Specification is not a replacement for the Owner Project Requirements, and it’s certainly not the starting point.
The OPR defines the “why”, while the URS defines the “what”

Together, they create the bridge between vision and execution, ensuring your cleanroom performs exactly as intended.

In cleanroom projects, success begins long before design drawings.
It begins with asking the right questions ,and documenting the right answers in the right order.

At Cleanroom Catalyst, we help clients develop clear Owner Project Requirements and structured User Requirement Specifications that align with their operational and compliance goals.
If you’re planning a new cleanroom or upgrading an existing one, let’s start from the top, with your true project intent.

Let’s Talk: www.cleanroomcatalyst.com