EN 15978 (buildings) vs EN 15804 (products) — which one when?

EN 15804 and EN 15978 are often confused — both regulate life cycle assessment in the construction sector. Actually they operate at different scales: EN 15804 produces an EPD for a single product; EN 15978 aggregates multiple EPDs to assess the life cycle performance of an entire building. Green-building certification (LEED, BREEAM, DGNB) calculations follow EN 15978, taking EN 15804 EPDs as inputs.

Functional-unit difference

EN 15804 functional units are product-specific: 1 m² of insulation at R=1 m²K/W, 1 ton of cement, 1 m³ of C30/37 concrete. EN 15978 functions at the building scale: 1 m² of gross internal area, or 1 m² of grossed-up area, under a "1 year reference service life" frame. Direct addition does not work — a building-level EN 15978 calculation must scale EN 15804 data by quantity and service life. An air conditioner with a 15-year service life equals four replacements over a 60-year building life.

A common modulary alphabet

The two standards share the A1-A5/B1-B7/C1-C4/D module alphabet. The A1-A3 module of an EN 15978 study is the weighted sum of all products' EN 15804 A1-A3 values (each by material quantity). B6 (operational energy) is meaningful at building level — it is typically MND on a product EPD because isolating one product's contribution is impractical. Hence B6 is reported at building, not product, level.

Whole Life Carbon (WLC) — the new term

In the UK and Scandinavia, the term "WLC (Whole Life Carbon)" is gaining ground; it is essentially the market re-naming of EN 15978's building-level GWP. WLC has two components: "Embodied Carbon" (A1-A5 + B1-B5 + C1-C4 + D — carbon embedded in materials) and "Operational Carbon" (B6 + B7 — operating carbon). Green-building platforms increasingly require WLC reporting; EPD data must align with this framing.

Practical implication for manufacturers

EN 15978 is not directly your concern as a manufacturer — it belongs to the architect or certification consultant. But for your EN 15804 EPD to feed cleanly into an EN 15978 calculation, follow a few practices: state the conversion between functional and declared unit explicitly (e.g. 1 m² of 60 mm insulation = X kg of product), report service life explicitly, and indicate how many replacements are needed within the building lifespan. These details help the building team use your EPD without friction.