How is an Environmental Product Declaration (EPD) calculated?

The calculation behind an EPD is a life cycle assessment. But it differs from an ordinary LCA in one way that governs everything: an EPD calculation is not free. Product category rules (PCR) fix in advance what you calculate and on which assumptions.

That constraint is not an obstacle but the reason EPDs exist. Two manufacturers’ declarations for the same product are comparable only because both followed the same rules.

Step 1 — Find and read the PCR

Before calculating, establish which product category your product falls into and which PCR applies to it. The PCR sets the declared unit, the mandatory modules, cut-off rules, end-of-life scenarios and the indicators to report. A calculation done under the wrong PCR is rejected outright in verification.

Different program operators can have different PCRs for the same product category. Decide which operator you will publish with at the outset, because that choice changes the rules of the calculation.

Step 2 — Set the declared unit

The PCR usually defines this for you: one m² of tile, one m³ of concrete, one tonne of cement, one metre of pipe. For performance-dependent products such as insulation, the unit also carries a performance reference — one m² achieving a given thermal resistance. Comparisons that do not preserve that reference are invalid.

Step 3 — Decide module coverage

EN 15804+A2 requires the A1-A3 product stage plus the C modules and Module D as minimum coverage; A4-A5 and the B modules are added depending on product type and PCR. Which modules you cover appears in the declaration’s cover information, and the reader’s correct interpretation depends on it.

Step 4 — Build the inventory

Here the expectation differs from an ordinary LCA: EN 15804 requires data on production processes to be site-specific. Energy consumption, raw material quantities, production waste and direct emissions must be primary data. Background database use is legitimate for the upstream chain of purchased inputs — it cannot substitute for your own site data.

Step 5 — Score the data quality

EN 15804+A2 makes a data quality rating (DQR) mandatory. Every significant inventory line is scored on temporal, geographic and technological representativeness and reported in the declaration. Optional in an ordinary LCA, this step cannot be skipped in an EPD.

Step 6 — Produce the result tables

The EN 15804+A2 indicator set is reported by module. Core indicators include GWP in three rows — fossil, biogenic and land use — plus ozone depletion, acidification, three kinds of eutrophication, photochemical ozone, abiotic resource depletion and water scarcity. Resource use, waste and output flow tables are added to these.

Step 7 — Verify and publish

The work does not end when the calculation does. An independent verifier audits PCR compliance, data quality and the report’s completeness; the program operator publishes the declaration publicly. Verification takes two to ten weeks depending on the operator, and typical validity is five years.