Embodied carbon modules A1 to A5, explained

Embodied carbon modules A1 to A5 are the life cycle stages covering everything emitted before a building is handed over. A1 to A3 form the product stage: raw material supply, transport to the factory gate and manufacturing. A4 is transport from the factory to site. A5 is the construction process itself. Added together they are upfront carbon, and on most new buildings they are the largest part of the whole life figure.

The modules come from the European standard on assessing the sustainability performance of buildings, and in the United Kingdom they are applied through the RICS whole life carbon assessment standard, which sets the scope, the study period and the reporting conventions a planning submission is expected to follow.

What the modules cover

The full set runs from A through D, and the A modules are only the beginning.

Module A0 was added in the current edition of the RICS standard and covers the pre-construction activities that earlier versions left out. It is small in most assessments and its absence is noticeable to a reviewer who is checking the scope.

Module D is the one most often misused. It captures the potential benefit of reuse, recovery and recycling beyond the building's life, and it is reported separately rather than deducted from the other modules. A submission that nets module D against A1 to A5 to reach a lower headline figure will be challenged.

Product stage against construction stage

A1 to A3 are usually reported as a single combined figure, because that is how environmental product declarations present them. The three sub-modules cover extraction and processing of raw materials, their transport to the manufacturing plant, and the manufacturing process including energy, water and factory waste.

A4 is transport to site, which depends on distance, mode and vehicle load factor. It is much smaller than people expect for most materials and much larger for heavy, low-value products moved a long way. Sourcing aggregate from 200 kilometres away instead of 30 changes A4 materially and changes A1 to A3 not at all.

A5 in the current standard is broken into three parts, and keeping them separate is what makes the figure useful. Pre-construction demolition sits in one, which matters on any site with existing structures. Construction activities cover site accommodation, plant, temporary works, energy and water use during the build. Material wastage covers offcuts, over-ordering, damaged goods and packaging, which is where the specification and the procurement approach show up.

That third part is the one a contractor can influence most directly, and it is routinely assessed using default wastage rates rather than project data. Say which you used.

Why upfront carbon dominates

Two things have made A1 to A5 the centre of attention.

The electricity grid has decarbonised substantially, which has reduced the operational carbon of a new building over its life. Meanwhile the materials have not changed much. The result is that on a new, well-insulated building with an efficient heat source, upfront carbon can exceed the whole of the modelled operational emissions over the assessment period.

The second reason is timing. Upfront carbon is emitted now, during construction, rather than spread over 60 years. In a policy environment concerned with near-term emissions, an emission today is not equivalent to the same emission in 2060, and that argument is increasingly made in decision-taking.

The practical consequence is that the design decisions with the biggest effect are made early: whether to retain an existing structure, how deep to go below ground, and what the frame is made of. By the time a scheme reaches technical design, the large moves are gone and only the specification remains.

Data sources and their quality

An assessment is only as good as the carbon data behind it, and data quality is the first thing a competent reviewer checks.

The best source is a verified environmental product declaration for the specific product from the specific manufacturer, prepared to the relevant European standard on product declarations. Next best is an industry-average declaration for the product type in the relevant market. Below that come generic databases and, at the bottom, figures taken from another project's assessment.

What matters for credibility is stating which you used, element by element, and being honest about the mix. Most assessments at planning stage are necessarily generic, because the products have not been selected, and a reviewer accepts that when it is declared. What they do not accept is a precise-looking total with no indication of its provenance.

Two further points. Declarations have a validity period and a geographic scope, so a declaration from another market for a product with different manufacturing energy is a weak substitute. And where a low-carbon option is assumed, such as a cement replacement level, the assumption has to be deliverable and worth securing in the specification.

Boundaries and what is left out

Every assessment draws a boundary, and the exclusions are as informative as the inclusions.

The RICS standard sets a minimum scope covering the main building elements: substructure, superstructure, finishes, fittings where fixed, and building services. Furniture, loose fittings and equipment are typically outside scope. External works are sometimes included and sometimes not, depending on the reporting requirement, and on a scheme with extensive landscaping and hard surfacing that choice moves the total.

State the exclusions explicitly and give the floor area basis. The result is normally expressed as kilogrammes of carbon dioxide equivalent per square metre of gross internal area, and a difference in how area was measured produces an apparent difference in performance that has nothing to do with the building.

Also state the study period. Sixty years is the convention, and comparing a 60-year assessment with a 100-year one without saying so is misleading even if unintentional.

Reporting conventions

A Whole Life Carbon Assessment that a reviewer can check has a predictable shape. This report type is one where councils expect a suitably qualified author, so professional review is strongly advised.

Report by module and by building element, so that a reader can see where the carbon sits rather than only the total. Give the upfront figure for A1 to A5 separately from the whole life figure. Keep module D separate and clearly labelled. State the standard and edition applied, the data sources by element, the floor area and its basis, the study period, and every exclusion. Where the scheme sits in London, use the reporting template the Greater London Authority requires for referable development, because a non-standard format will be returned.

Keep the operational energy module consistent with the Energy Statement. Two documents giving different operational figures is among the easiest inconsistencies for a reviewer to spot.

Using the results to change a design

An assessment that arrives after the design is fixed is a compliance document. One that arrives early is a design tool, and the difference is worth insisting on.

1. Test retention of any existing structure against demolition and rebuild, including the module A5 demolition figure and the pre-redevelopment audit findings.
2. Test the substructure, because basements and deep foundations carry a large share of upfront carbon for little floor area.
3. Test the frame options at concept stage, when changing them is still possible.
4. Reduce material quantity before changing material type, since a lighter structure beats a lower-carbon heavy one in many cases.
5. Address the facade, which is often the second largest element after the structure.
6. Set wastage targets and procurement requirements that the contractor can be held to.
7. Re-run the assessment at the end of technical design and again as built, so the figure reported is the figure delivered.

Where the scheme also needs a Circular Economy Statement or a Pre-redevelopment Audit, keep the reuse assumptions identical across all three, because they all feed the same numbers.

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