Introduction
Two suppliers send you an EPD for what looks like the same product, and the carbon figures do not match. Before assuming one is wrong, check the rules each EPD was built on. The Product Category Rules (PCR) behind an EPD govern how it is calculated — and differences in the PCR, the programme or the standard version can produce legitimately different numbers for similar products.
What a PCR Governs
A PCR sets the calculation rules for a product category: the system boundary, the declared or functional unit, the allocation method, the end-of-life scenarios and the reference service life. An EN 15804 EPD must declare the PCR it follows, because without it the result cannot be reproduced or compared.
Why the Same Product Can Show a Different Figure
| Source of difference | Effect |
|---|---|
| Different PCR | Different boundaries, allocation or scenarios — results are not directly comparable |
| Different programme operator | Programme-specific rules and interpretations vary |
| Different EN 15804 version (+A1 vs +A2) | Different indicators and GWP reporting; figures are not on the same basis |
| Different declared unit or reference service life | The number refers to a different quantity or lifespan |
| Different data vintage and geography | Older or different-region data shifts the result |
The Comparability Rule
EPDs are comparable only when they share the same PCR, the same declared/functional unit, the same life-cycle modules and the same EN 15804 version. Where a manufacturer can choose between programmes or PCRs, there is an incentive to select the most favourable basis — so the buyer’s job is to confirm the basis before comparing, not to compare the headline numbers blindly. Read each EPD properly first: see how to read an EPD like an auditor and how Module D can shift a figure.
How to Compare Correctly
- Confirm both EPDs cite the same PCR and EN 15804 version.
- Check the declared unit and modules match.
- Only then compare the GWP — and check the data vintage and geography.
How EPD Polska / Multicert Can Help
We prepare EPDs on a transparent PCR basis and help buyers compare third-party EPDs correctly. Contact us.
FAQ
Can I compare two EPDs from different programmes?
Only if they follow the same PCR, modules, unit and standard version. Otherwise the comparison is not valid.
Does a lower number always mean a better product?
Not if the EPDs are built on different rules. Confirm the basis before drawing a conclusion.