Life-Cycle Stages (Modules A1–D)
When one building’s carbon figure looks half another’s, the difference is often not the building at all — it is which slices of the life cycle each number counted. A “cradle-to-gate” material figure and a “whole-life” building figure can differ by more than tenfold, yet both are correct. What makes them comparable, or exposes them as not, is a shared set of labels for every stage of a building’s life.
Those labels are the life-cycle modules. Modules A1–D are the EN 15978 framework that names every stage of a building’s or product’s life cycle — turning vague phrases like “embodied” or “whole-life” carbon into precise, comparable definitions.
The life-cycle modules A1–D are the standardised labels the European standard EN 15978 (and EN 15804 for products) gives to each life-cycle stage: A product and construction (A1–A5), B use (B1–B7), C end of life (C1–C4), and D benefits beyond the boundary. They define exactly what embodied carbon, upfront carbon, operational carbon, and whole-life carbon each include, so figures can be compared like with like.
Definition — A Label for Every Stage
The life-cycle modules are a standardised system of codes that label each stage in the life of a building or construction product. They are defined by the European standard EN 15978 for whole buildings and EN 15804 for individual products, and they run from A1 (raw-material supply) through to D (benefits beyond the system boundary). Each module is a precisely defined slice of the life cycle, so that a carbon assessment can be broken down, reported, and compared stage by stage.
Their purpose is comparability and transparency. Before the modules, “embodied carbon” or “whole-life carbon” meant slightly different things to different people, and figures could not be trusted to cover the same ground. The module framework fixes that: an LCA result or an Environmental Product Declaration states which modules it includes, so a reader knows exactly what is — and is not — in the number. Every headline term in building carbon, from cradle-to-gate to whole-life, is now simply a named group of these modules.
The Full Module Map (A1–D)
The modules are organised into four life-cycle stages — A (product and construction), B (use), C (end of life), and D (beyond the boundary):
| Module | Name | What it covers |
|---|---|---|
| A1 | Raw material supply | Extracting and supplying raw materials |
| A2 | Transport | Transport of materials to the manufacturer |
| A3 | Manufacturing | Making the product (A1–A3 together = cradle-to-gate) |
| A4 | Transport | Transport of the product to the building site |
| A5 | Construction / installation | Installing the product; site activities, waste (A1–A5 = upfront carbon) |
| B1 | Use | Emissions from the product in normal use |
| B2 | Maintenance | Routine maintenance over the service life |
| B3 | Repair | Repairing damage or faults |
| B4 | Replacement | Replacing components that wear out |
| B5 | Refurbishment | Major refurbishment during the building’s life |
| B6 | Operational energy | Energy used to run the building — operational carbon |
| B7 | Operational water | Water used in operation — operational |
| C1 | Deconstruction | Demolition or dismantling at end of life |
| C2 | Transport | Transport of waste for processing/disposal |
| C3 | Waste processing | Processing for reuse, recovery, or recycling |
| C4 | Disposal | Final disposal (C1–C4 = end of life) |
| D | Beyond the boundary | Net benefits/loads from reuse, recovery, recycling, exported energy — reported separately |
In practice a product Environmental Product Declaration usually reports A1–A3, C1–C4, and D; the transport-to-site (A4), construction (A5), and use (B) modules are project-specific — they depend on the building, not the product, so they are added when a whole-building assessment is assembled.
How the Modules Group: The Terms You Know
The familiar names for building carbon are all just defined groups of these modules. This is where the framework earns its keep — each term becomes unambiguous:
| Term | Modules |
|---|---|
| Cradle-to-gate | A1–A3 |
| Upfront carbon | A1–A5 |
| Embodied carbon | A1–A5 + B1–B5 + C1–C4 (everything except operational) |
| Operational carbon | B6–B7 |
| Whole-life carbon | A1–A5 + B1–B7 + C1–C4 (with D reported separately) |
Read against the map above, the definitions are exact: embodied carbon is every module except the operational pair B6–B7; whole-life carbon adds those back; and module D always sits outside the total. When a figure is quoted, the right question is simply “which modules?”.
Module D — Beyond the Boundary
Module D is the one that most often causes confusion, so it is worth isolating. It captures the net benefits and loads that occur outside the assessed system’s boundary — chiefly the value of materials recovered for reuse or recycling at end of life, and any energy exported from the process. Recovering a tonne of steel or aluminium displaces the production of virgin material elsewhere, and module D records that avoided burden.
Because module D reaches beyond the system boundary and depends on assumptions about a future, external system, EN 15978 requires it to be reported as a separate figure — never blended into the A-to-C total. For galvanised steel the module D credit is around -1.11 kg CO₂e per kg [GreenCalculus materials.steel.galvanised.module_d · OEKOBAUDAT 2024 · v2026.203], a real and significant recovery benefit, but it is shown on its own line so a reader can see the gross life-cycle carbon and the potential recovery credit distinctly. This mirrors the wider land-and-removals discipline of never netting a credit into a gross total.
One Material Across the Modules
Seeing real numbers by module makes the framework concrete. Here is the live per-module carbon of one kilogram of galvanised steel, as a product EPD reports it — production (A1–A3), the end-of-life modules (C1–C4), and the beyond-boundary credit (D):
| Module | Stage | kg CO₂e / kg |
|---|---|---|
| A1–A3 | Product (cradle-to-gate) | 2.48 |
| C1 | Deconstruction | 0.0377 |
| C2 | Transport | 0.00721 |
| C3 | Waste processing | 0 |
| C4 | Disposal | 0.00048 |
| D | Beyond boundary (recovery) | -1.11 |
Galvanised steel, kg CO₂e per kg by module (ÖKOBAUDAT, live). Production (A1–A3) dominates; the end-of-life modules (C1–C4) are tiny for steel; module D is a substantial recovery credit (negative), shown on its own because it is reported separately from the A-to-C total. Bar width is magnitude; the D label keeps its negative sign.
Common Confusions
- Assuming “embodied carbon” means A1–A3. Cradle-to-gate (A1–A3) is only the product stage. Embodied carbon also includes construction (A4–A5), maintenance and replacement (B1–B5), and end of life (C1–C4).
- Netting module D into the total. The reuse/recovery credit (D) is reported separately, beyond the system boundary — never subtracted from the A-to-C figure.
- Comparing figures with different modules. A cradle-to-gate number and a whole-life number cover different modules and are not comparable. Always check which modules each includes.
- Forgetting that A4–A5 and B are project-specific. A product EPD’s A1–A3 is not the whole building; transport to site, installation, and use depend on the project and are added at building level.
- Treating B6–B7 as embodied. Operational energy and water (B6–B7) are operational carbon, not embodied — they are the one part of the use stage that sits outside embodied carbon.
Dataset — the full factor set behind this term, versioned with source provenance and downloadable as CSV with a citable Zenodo DOI, is published as the Ökobaudat embodied carbon factors dataset.
Frequently Asked Questions
They are the standardised labels that the European standards EN 15978 (buildings) and EN 15804 (products) give to every stage of a building’s or product’s life cycle. They are grouped into four stages: A covers product manufacture and construction (A1–A5), B covers the use phase (B1–B7), C covers end of life (C1–C4), and D covers benefits and loads beyond the system boundary such as reuse and recycling. Each module is a defined slice of the life cycle, which lets a carbon assessment state exactly which stages it counts and lets two figures be compared only when they cover the same modules.
They are progressively wider boundaries. A1–A3 is the product stage, or cradle-to-gate — raw material supply, transport to the factory, and manufacturing. A1–A5 adds transport to site (A4) and construction/installation (A5), and is known as upfront carbon — everything emitted before the building is occupied. A–C extends all the way through the use stage (B) and end of life (C) to give whole-life carbon. Embodied carbon sits between them: it is A1–A5 plus the material use modules B1–B5 plus C1–C4, excluding only the operational modules B6–B7. Module D, the reuse/recovery credit, is always reported separately from all of these.
Module D captures the net benefits and loads that occur beyond the assessed system’s boundary — mainly the value of materials recovered for reuse or recycling at end of life, and any energy exported from waste processing. Recovering steel or aluminium, for example, displaces the production of new virgin material elsewhere, and module D records that avoided emission as a credit — around -1.11 kg CO₂e per kg [GreenCalculus materials.steel.galvanised.module_d] for galvanised steel. Crucially, EN 15978 requires module D to be reported as a separate figure and never blended into the A-to-C total, because it depends on assumptions about a future, external system. It lets a reader see the gross life-cycle carbon and the potential recovery benefit distinctly.
Embodied carbon is every module except the operational ones. In module terms it is A1–A5 (product and construction), plus B1–B5 (maintenance, repair, replacement, refurbishment — the material events during use), plus C1–C4 (end of life). The only modules it excludes are B6 and B7, the operational energy and water use, which are operational carbon. Whole-life carbon is embodied plus operational — that is, all of A, B, and C together. Module D, the beyond-boundary recovery credit, is reported separately and is not part of either the embodied or the whole-life total.
Because some modules depend on the building, not the product. A product Environmental Product Declaration typically reports A1–A3 (production), C1–C4 (end of life), and D (recovery), because these are properties of the material itself. But transport to site (A4), installation (A5), and the whole use stage (B) depend on where and how the product is used — the distance to the specific site, the construction method, the building’s design life and maintenance regime. These project-specific modules are added when a whole-building assessment is assembled from the individual products, which is what a tool such as the whole-building LCA calculator does.
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