Modules A1 to A5 in a Whole Life Carbon Assessment

Whole life carbon modules a1 to a5 are the upfront half of the assessment: everything emitted before the building is handed over. A1 to A3 covers the products, A4 covers getting them to site, A5 covers what happens on site including demolition and waste. Together they are the numbers a planning officer looks at first, because they are the emissions a decision can still influence.

The later modules matter for the whole life figure. They do not change if the scheme is redesigned in the way that A1 to A5 do.

Which modules the planning assessment reports

The module structure comes from BS EN 15978, and the RICS professional standard on whole life carbon assessment for the built environment, now in its second edition, sets out how to apply it in the UK. A Whole Life Carbon Assessment submitted with a planning application reports every module, with A1 to A5 given separately as upfront carbon.

Module D is reported separately and is never netted off the total. That rule exists because reuse and recovery benefits accrue to a future project, not to this one, and a scheme that subtracts them flatters itself.

A1 to A3 and the data quality question

Product stage emissions usually make up the largest share of upfront carbon, and they are calculated by multiplying quantities by carbon factors. So the assessment is only as good as the quantity take-off behind it.

At planning stage the take-off is necessarily approximate. State that plainly, and state the basis: floor areas by element, assumed structural grid and slab depths, assumed façade build-up, assumed foundation type. An assessment that reports a single figure without the element breakdown cannot be reviewed by anyone.

Carbon factors follow a hierarchy. Product-specific environmental product declarations prepared to EN 15804 sit at the top, followed by sector average declarations, then generic database values. Early-stage assessments lean on generic data, and that is acceptable provided the report says so and identifies the elements where a specific declaration would change the answer.

Biogenic carbon in timber is reported according to the RICS method rather than treated as a free reduction. Sequestered carbon is recorded at the product stage and the corresponding release appears at end of life, so a timber building does not simply score a negative number.

A4 and the transport assumptions

Module A4 is small in proportion but easy to get wrong, and it is where reviewers find unsupported assumptions.

Report the distance and mode for each major material stream: concrete from a batching plant, steel from the rolling mill or the stockholder, timber including any sea leg, façade units from the fabricator. Where the supplier is unknown, use the standard default distances from the RICS standard rather than an optimistic guess, and say which defaults you used.

Two things move A4 materially. Imported material with a long sea and road leg, and heavy low-value materials such as aggregate and concrete where the tonnage is large even if the distance is short.

A5 and what the second edition changed

The second edition of the RICS standard subdivides module A5 so that the site stage is no longer a single lump. In broad terms it separates the carbon of pre-construction demolition and site preparation, the carbon embodied in construction waste, and the carbon of construction activities themselves such as plant, temporary works, site accommodation and energy use.

That subdivision matters for planning. Demolition carbon becomes visible, which strengthens the case for retention and reuse and connects the whole life carbon work directly to the retrofit-first argument in local policy. It also means that a scheme demolishing an existing building carries that carbon in its own assessment rather than treating the site as a clean slate.

Construction waste is the other half. Waste rates by element feed straight into A5, so a design with high off-site prefabrication and low wet trades reports lower waste carbon, and the assessment should state the waste rates assumed rather than accepting a default silently.

Where a scheme involves demolition, a Pre-redevelopment Audit records what is in the existing building and what can be reused, and the reuse quantities should be consistent between that document, the Circular Economy Statement and the A5 figures.

Reporting units and benchmarks

Results are reported in kilograms of carbon dioxide equivalent per square metre of gross internal area, written kgCO2e/m2 GIA, and the area basis has to be stated because a figure calculated on GIA is not comparable with one calculated on net internal area or on a habitable room count.

Report upfront carbon as A1 to A5 and whole life carbon as A to C, with module D shown alongside. Give the figure for the structure separately from the façade and the services, because that is the breakdown a reviewer needs to see where the carbon sits.

Benchmarks are published in the Greater London Authority guidance for referable schemes, with aspirational and target figures by building type, and other bodies publish their own. Take the current numbers from the source document rather than from a secondary summary, because they have been revised and will be again.

Illustrative example: concrete against timber

Illustrative example. A six-storey residential block is assessed twice at concept stage, once with a reinforced concrete frame and once with a cross-laminated timber frame on a concrete transfer structure.

The timber option reports lower A1 to A3 for the superstructure and higher A4, because the panels travel further. Its A5 figure falls, since a prefabricated frame generates less site waste and a shorter programme with less plant. Substructure carbon barely moves, because the ground conditions dictate the piling either way.

Treat that as a comparison rather than a verdict. It only holds if both options carry the same substructure assumptions, the same façade and the same service life, and if the biogenic carbon is reported to the same method in each. The moment one option quietly uses a lighter façade, the comparison stops meaning anything. All figures in this example are illustrative.

Why B, C and D stay separate

Use stage carbon, particularly module B4 replacement, can rival upfront carbon over a 60-year study period, and it is driven by assumed service lives for façade elements, finishes and plant. Those assumptions are judgement calls, so mixing B4 into a headline upfront figure hides the uncertainty.

End of life modules C1 to C4 depend on waste treatment scenarios decades away, which are unknowable in any precise sense. Reporting them separately keeps the honest part of the assessment honest.

For planning purposes, the useful discipline is to treat A1 to A5 as the number the design team can act on now, and the rest as context. The Energy Statement deals with operational carbon under the energy hierarchy, and the two documents should share the same floor areas and the same building description.

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