Can I publish an EPD with both a reference unit and a functional unit?

Yes. EN 15804 allows dual reporting, but you must explain why and ensure both units sit inside the same system boundary.

Do reviewers ever reject an EPD solely for a bad unit definition?

Absolutely. Under GPI 5.0.0 reviewers can flag unclear or missing performance parameters as a major non-conformance, halting publication.

Is the reference unit always per kilogram?

No. It can be mass, area, volume, or a single piece. Follow the PCR example list for your category.

Will the choice of unit change my product’s LEED contribution?

Indirectly. LEED calculators read the values you report. If your unit type mismatches the calculator assumption, the contribution might read as zero even if the impacts are low.

Functional Unit vs Reference Unit: Get Them Right

Why the fuss about units?

A life-cycle assessment crunches thousands of data points, yet all results are divided by one tiny denominator. Pick the wrong denominator and the math misleads. Pick the right one and your product story snaps into focus. Simple, but not easy.

Functional unit in plain English

Think of the functional unit as the job description. It defines the service a product delivers (what, how much, for how long). Example: Providing thermal resistance of R-3.5 for 50 years over 1 m² of wall. EN 15804+A2 now demands a fuller description exactly because buyers want performance certainty (IGBC, 2024). If your EPD includes use-phase impacts, you almost always need a functional unit.

Reference (declared) unit when function is fuzzy

Many products have multiple end uses or are sold long before the design team decides how they will be installed. In that case the program operator lets you swap in a reference unit, often called a declared unit: 1 kg of coating or 1 m³ of ready-mix concrete. The new Dutch NMD guidance spells out when this shortcut is acceptable and what extra notes must accompany it (NMD, 2025).

Same product, two lenses

Picture a cement board panel. A cradle-to-gate EPD might declare impacts per kilogram. Add installation and 60-year service life, and the functional unit could become covering 1 m² of facade for 60 years. Numbers change, rankings shift. Recent comparative studies show as much as a 40 percent swing in global warming potential once you switch units (IJLCA, 2024).

What specifiers really compare

Project teams filter EPDs in digital tools by mass, area, or service life. If your unit type mismatches the competitor list, you are invisible. Re-publishing an EPD just to fix units costs weeks and reviewer fees. Better to choose right first.

Quick decision tree for manufacturers

Does the PCR or operator force a functional unit? If yes, stop here.
Is the primary application known and stable? Choose functional.
Are there several credible applications? Go reference unit, add clear installation assumptions in the annex.

2025 operator checkpoints

Program operators are raising the bar. EPD International’s GPI 5.0.0 flags incomplete unit definitions as a high-risk non-conformance and allows reviewers to reject at pre-verification (EPD International, 2024). Expect tighter wording and cross-checks against service life tables.

Key takeaways for busy teams

Units rule comparability and credibility.
Functional unit equals performance, reference unit equals quantity.
Read the PCR first, then draft the unit line, not the other way round.
Double-check against operator checklists before data crunching starts.

Its easy to mix them up, but getting them right saves rework and keeps your product on the spec sheet.