System boundary: cradle-to-gate, -grave, -cradle — which when?
System-boundary choice defines which life cycle modules your study includes. The three core scopes and selection criteria.
By clca Editorial TeamLast updated
The system boundary is the most consequential methodological decision in an LCA — it defines what is included and what is left out. The wrong boundary distorts results systematically. EN 15804+A2 supports three main scopes: cradle-to-gate, cradle-to-grave and cradle-to-cradle.
Cradle-to-gate (A1-A3)
From raw materials to the factory gate. Includes A1 (raw material supply), A2 (transport) and A3 (manufacturing). It is the default scope for construction materials because the product passes out of "manufacturer responsibility" beyond this point — installation, use, and end-of-life rest with the contractor or building owner. Cradle-to-gate is the minimum EPD scope; A4-D modules are flagged MND in the modulary table.
Cradle-to-grave (A1-C4)
From raw materials to disposal — covers the entire life cycle. A1-A5 (production and construction), B1-B7 (use), C1-C4 (end of life). Green-building certifications (LEED, BREEAM, DGNB) require cradle-to-grave scope; building-level LCA (EN 15978) depends on it. Module D is optional within this scope — reported if available, MND otherwise.
Cradle-to-cradle (A1-D)
Cradle-to-cradle extends cradle-to-grave with Module D — reporting beyond-system-boundary benefits (the recycle credit). The term references circular-economy thinking — emphasising that the product creates value in its second and third lives. Recycle-heavy products like steel and aluminium prefer this scope because Module D yields a positive credit. For plastics, Module D contributions are modest, so the gap to cradle-to-grave is smaller.
Choosing the right scope in 4 questions
- 1. What is my EPD use case? Marketing (cradle-to-gate suffices), building certification (cradle-to-grave required), environmental claim (cradle-to-cradle preferred)
- 2. Is the production geography the same as installation/end-of-life geography? If different, averages are insufficient and local data is needed
- 3. Is there a real secondary market for Module D? If not, stopping at cradle-to-grave is safer
- 4. What does the PCR Part B require? Some categories mandate cradle-to-grave (e.g. wood)
Tags
- system boundary
- cradle-to-gate
- cradle-to-grave
- cradle-to-cradle
- LCA scope
- A1-A3 modules
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