A life-cycle global warming potential (GWP) calculation under the EPBD follows EN 15978 and covers modules A1 to C — product manufacture, transport to site, construction, use and replacement, and end of life — assessed over a reference study period of 50 years (Delegated Regulation (EU) 2026/52, Union framework for the national calculation of life-cycle GWP). Modules D1 and D2, benefits beyond the system boundary, are required by Annex III and reported separately rather than netted off the headline figure.
The modules are not jargon for its own sake. They are the reason two carbon figures for the same building can differ by a factor of two and both be correct: they were drawn around different boundaries.
The short version
- A1–A3, product stage — extraction, transport, manufacture. Usually the largest single block for a new building.
- A4–A5, construction stage — transport to site, and site activity including waste.
- B, use stage — required: B1 in-use emissions, B2 maintenance, B3 repair, B4 replacement, B6 operational energy. Optional: B5 refurbishment, B7 operational water, B8 user activities.
- C1–C4, end of life — demolition, transport, waste processing, disposal.
- D1 and D2, beyond the boundary — reuse/recycling potential and exported utilities. Required by Annex III, and reported separately rather than subtracted from the headline.
- A1–A5 together are “upfront carbon” — everything emitted before the building is handed over. It is already spent on day one.
- The reference study period is 50 years, which is what makes replacement cycles in B4 material.
Why does the module boundary matter so much?
Because it decides what is counted.
| Module | Stage | Annex III status |
|---|---|---|
| A1–A3 | Product — extraction, transport, manufacture | Required |
| A4–A5 | Construction — transport to site, site activity | Required |
| B1–B4 | Use — in-use emissions, maintenance, repair, replacement | Required |
| B5 | Refurbishment | Optional |
| B6 | Operational energy | Required |
| B7 | Operational water | Optional |
| B8 | User activities | Optional |
| C1–C4 | End of life — demolition, transport, processing, disposal | Required |
| D1, D2 | Beyond the boundary — reuse/recycling potential, exported utilities | Required, reported separately |
Quote a figure covering A1–A3 only and you have described the materials leaving the factory gate. Quote A1–A5 and you have added getting them to site and putting them together. Quote A–C and you have described the whole life. Each is a legitimate number. None is comparable to the others.
This is the single most common source of confusion when comparing buildings, and it is why any credible figure states its modules alongside it. A building “at 400 kgCO₂e/m²” means nothing until you know where the boundary was drawn.
What sits in each module?
A1–A3, product stage. Raw material supply, transport to the factory, and manufacturing. This is what an Environmental Product Declaration (EPD) reports, and for most new buildings it is the largest contributor. Structure and facade dominate — see CLT vs concrete vs steel.
A4–A5, construction stage. A4 is transport from factory to site. A5 covers site activity: plant, temporary works, and — often underestimated — material wastage. A5 is where offcuts and over-ordering appear as carbon.
B1–B7, use stage. B1 is emissions in use, such as carbonation of concrete. B2–B3 are maintenance and repair. B4 is replacement, and over a 50-year period this is where short-life elements become expensive: a facade sealant or floor finish replaced three times carries three times its embodied carbon. B6 and B7 are operational energy and water — the part that has historically dominated, and increasingly does not (embodied vs operational carbon).
C1–C4, end of life. Demolition or deconstruction, transport of waste, processing, and final disposal. Scenario-dependent by nature, since nobody knows how a building will be taken apart in 2076.
D, beyond the system boundary. The credit for materials that go on to be reused or recycled. Reported separately and deliberately kept out of the headline: netting it off lets a building claim benefit for a recycling event that has not happened and may never happen.
How are the unknowable parts handled?
With default scenarios, and this is a feature rather than a fudge.
Modules B and C describe events decades away. No designer knows the 2070 demolition method or the real replacement interval of a sealant. The framework therefore allows default scenarios to fill gaps, so that two assessors calculating the same building reach comparable answers instead of each inventing plausible assumptions.
The practical consequence: A-stage figures are estimates of real quantities; B and C figures are estimates of scenarios. They deserve different levels of confidence, and a well-presented assessment says which is which.
Which modules will actually be mandatory?
Delegated Regulation (EU) 2026/52 requires the calculation to follow the relevant parts of EN 15978. The Directive itself does not name the standard. Precisely which modules become a minimum requirement — and how much latitude Member States retain — is set through the delegated act and national implementation, and remains subject to national roadmaps due 1 January 2027 (full EPBD timeline).
The honest planning position: assume A1–C. If you scope an assessment to A1–A3 because it is cheaper, you are building a baseline you will have to redo.
Where do the numbers themselves come from?
Every module needs two inputs: a quantity and a carbon factor.
Quantities come from the model or the schedule — cubic metres of concrete, square metres of glazing. Factors come either from generic datasets such as the ICE database or from product-specific EPDs. Generic data is appropriate early, when the product is not chosen; EPDs are what a certified assessment expects later.
The quantity side is where early-stage error concentrates. A carbon factor is wrong by a few percent. A missed slab is wrong by a hundred.
What does this mean in practice?
Upfront carbon is the part you control. A1–A5 is spent before handover and cannot be recovered by good operation afterwards. It is also decided early, at concept stage (pre-assessment material intelligence).
B4 rewards durability. Over 50 years, specifying something that lasts twice as long halves its replacement carbon. This rarely shows up in an A1–A3 comparison, which is exactly why A1–A3 comparisons mislead.
C and D reward design for disassembly — but only if the building can actually be taken apart. See circularity pathways.
State your boundary, always. Internally and externally. Most carbon disputes are boundary disputes wearing a disguise.
Frequently asked questions
What is upfront carbon? Modules A1–A5: everything emitted producing and assembling the building, before it is occupied. It is the portion already committed at handover.
Is operational energy included? Yes, as B6, within the whole-life figure. This is why the EPBD number is life-cycle GWP rather than embodied carbon alone.
Why 50 years? It is the reference study period set for the calculation. It is a convention for comparability, not a prediction of how long the building stands.
Can module D offset a high A-stage figure? No. D is reported separately and deliberately excluded from the headline, precisely so that anticipated future recycling cannot mask high upfront carbon today.
Does this apply to refurbishment? The EPBD disclosure duty targets new buildings, but the same module structure applies to any EN 15978 assessment — and retained material carries no new A1–A3 burden at all, which is the whole argument in refurbishment vs demolition.
Where this leaves you
The module structure is what makes carbon figures comparable. Without it, “our building is 380” is a number without a claim attached.
Elementa reports quantities and carbon by building system on the EN 15978 model, so an early figure carries its boundary with it and hands a clean, auditable baseline to whoever performs the certified assessment.
Early figures are indicative and directional. They inform decisions; they do not replace a verified life-cycle assessment.
Sources: European Commission — calculation framework for new building life-cycle GWP; Delegated Regulation (EU) 2026/52 (EUR-Lex); Whole Life-Cycle GHG emission reporting for buildings (EU guidance). Verified August 2026.