Turning EPD data into a Scope 3 inventory

If you collect EPDs from suppliers, you hold the highest-quality data available for a Scope 3 inventory: product-specific, independently verified, in a standard format. But the EPD’s module structure does not map one-to-one onto the GHG Protocol’s categories; without a correct mapping you end up either under- or double-counting.

The core mapping

• A1-A3 (product stage) → Category 1: purchased goods and services
• A4 (transport to you) → Category 4: upstream transport and distribution
• A5 (installation, on-site waste) → Category 1 or Category 5, depending on who manages the waste
• B modules (use) → Category 11: use of sold products — for your own product
• C modules (end-of-life) → Category 12: end-of-life treatment of sold products — for your own product
• Module D → maps to no category; it is outside the system boundary and is not counted in the inventory

That last item matters most. Module D reports potential benefits from recovery and is typically negative. Subtracting it from the Scope 3 total in a corporate inventory breaches GHG Protocol rules and will be rejected in verification. Module D can be reported separately as information, but it cannot be netted off the total.

Unit conversion

An EPD reports per declared unit, and that unit is not always a kilogram: it may be one m² of insulation board, one m³ of concrete, one metre of pipe or a thousand bricks. Converting to Scope 3 means expressing your annual purchase volume in the same unit.

Insulation carries an extra trap: the declared unit is usually defined for a specific thermal resistance. Comparing two products’ per-m² values directly compares different performance levels. That performance reference has to be preserved when converting purchase volumes.

Scope and gas alignment

Under EN 15804+A2, GWP is reported in three rows: fossil, biogenic and land use. Scope 3 uses total GWP, but the sign of the biogenic row needs care. If biogenic carbon bound in the product is reported negative and that product is an input in your inventory, carrying that negative straight across is misleading — the carbon is ultimately released at the product’s end-of-life.

The consistent approach in practice is to track biogenic carbon separately and build the headline total on fossil GWP. That aligns both with the GHG Protocol’s expectation of separate biogenic reporting and with EN 15804+A2’s indicator structure.

Filling the gaps where EPDs are missing

No supply chain has an EPD for every line. A hybrid approach is required: lines with EPDs use primary data, the rest are modelled with background database activities. What matters is recording which line came from which source and assigning the data quality score accordingly.