Upfront carbon in modules A1 to A5

Upfront carbon covers modules A1 to A5 of a building's life cycle: the product stage, the transport of materials to site, and the construction process itself. Under BS EN 15978 those modules are A1 raw material supply, A2 transport to the factory, A3 manufacturing, A4 transport to site and A5 the construction and installation process. Everything in A1 to A5 is emitted before anyone occupies the building, which is why it has become the figure planning authorities compare schemes on.

Operational carbon can be improved later by changing the heat source or the grid. Upfront carbon cannot. Once the concrete is poured, that number is fixed for the life of the building.

What the modules cover

A1 to A3, taken together, are the product stage: extraction, processing, transport between production steps and manufacture, reported for each material in the building. Most published product data covers this cradle-to-gate scope.

A4 is transport from factory gate to site, which depends on distance and mode. It is often small in proportional terms and occasionally large, as with imported stone or a long haul of excavated material.

A5 is the construction process. The RICS whole life carbon methodology subdivides it so that pre-construction demolition and site clearance, on-site construction activities including plant and temporary works, and construction waste are each reported separately rather than bundled into one figure. That split matters on a redevelopment, because demolition of an existing structure can be a large part of the total and gets lost if A5 is reported as a single number.

The rest of the life cycle sits outside upfront carbon. B1 to B7 cover use, maintenance, repair, replacement and operational energy and water. C1 to C4 cover end of life. Module D sits outside the system boundary altogether.

Why upfront carbon is the comparable figure

Two schemes on the same site can be compared on A1 to A5 because the modules rest on decisions already made: structural system, foundation type, facade build-up, whether the existing building is kept.

Later modules depend on assumptions nobody can verify. A 60-year service life with two facade replacements is a projection, and small changes to replacement cycles swing the B modules more than any design decision. Operational modules depend on grid decarbonisation forecasts.

So when an application compares demolition and rebuild against retention and retrofit, the honest comparison is upfront carbon first, with the later modules reported but treated as a sensitivity. The full set of modules and how they fit together is set out in our piece on embodied carbon and the lifecycle modules from A1 to D.

Data sources and their quality

There is a hierarchy, and reviewers look for it:

1. A product-specific Environmental Product Declaration from the manufacturer, verified to the European standard for construction product declarations
2. An industry average or sector declaration for the material type
3. A generic database figure with a stated source and date
4. An estimate by analogy, which should be flagged as such

Mixing the levels is normal. Reporting which level each material used is what separates a credible assessment from a spreadsheet exercise. A data quality statement listing the main elements and the source for each takes a page and answers most of a reviewer's first questions.

Dates matter too. Product declarations expire, and a figure drawn from a withdrawn declaration is not evidence. Cement and steel data in particular have moved as producers change fuel and recycled content.

Module D and why it sits outside targets

Module D covers benefits and loads beyond the system boundary: the carbon credit claimed for materials that will be reused or recycled after the building's life, and for energy exported from on-site generation.

It is reported separately and never netted off A1 to A5. The reason is double counting. If a steel frame carries a recycled content benefit in A1 because it was made from scrap, and then claims a further credit in module D for being recyclable at end of life, the same benefit has been counted twice across the supply chain.

Biogenic carbon follows a similar logic. Sequestered carbon in timber is reported, with the end-of-life release reported in the C modules, so a timber building's apparent advantage depends on what happens to the material afterwards rather than on the storage alone.

Treat module D as context for a circular economy argument, which is where it does useful work, and keep it out of the headline figure. That reasoning belongs in a circular economy statement rather than in the carbon total.

Reporting conventions and units

Report in kilograms of carbon dioxide equivalent per square metre of gross internal area, state the floor area used, and state the reference study period even when reporting upfront carbon only.

Name the assessment stage honestly. A figure produced at concept design, before the structural grid is fixed, carries wide uncertainty, and presenting it as a verified result invites a condition requiring a post-construction reassessment.

A whole life carbon assessment prepared for planning should follow the RICS methodology where the local policy calls for it, and the Greater London Authority's reporting template where the scheme is referable. Councils usually expect a suitably qualified author for this work, and professional review is strongly advised.

An illustrative comparison of two structural options

Take a six-storey residential block on a cleared site, assessed at RIBA Stage 3, compared as a reinforced concrete flat slab frame against a cross-laminated timber frame with a concrete transfer structure at ground level.

The concrete option carries most of its upfront carbon in A1 to A3 for the frame and in the piled foundations. The timber option reduces the frame contribution and reports sequestered carbon, but it needs a different foundation solution, more fire protection and a heavier facade fixing strategy, so the saving is smaller than the frame comparison alone suggests. The A5 figures also differ, because the timber option has a shorter site programme and fewer wet trades.

This comparison is illustrative and gives no figures, because the answer depends on span, grid, soil conditions and the data sources used. The point is the shape of the comparison: compare whole systems at the same design stage, not materials in isolation.

What a reviewer checks first

In order, from experience of reading these:

The gross internal area and whether it matches the planning drawings. The scope, specifically whether substructure, external works and MEP services are included. Whether A5 separates demolition from construction activities. The data quality table. Whether module D has been netted off anywhere. And whether the comparison baseline, if one is claimed, is a real alternative design rather than a notional worst case.

The last of those is where assessments most often fail. A retention option dismissed as unviable in one sentence, with no carbon figure attached, will not satisfy a council that has a policy requiring the option to be tested. Price the comparison properly or do not claim it, and keep a pre-redevelopment audit alongside it where material reuse forms part of the case.

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This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.