Embodied carbon and the lifecycle modules from A1 to D

Embodied carbon is the greenhouse gas emitted in making, transporting, installing, maintaining and eventually removing a building, as distinct from the emissions from running it. An embodied carbon assessment quantifies that across defined lifecycle modules, and in the UK the method that matters is the RICS whole life carbon assessment standard, which builds on the modular structure set out in BS EN 15978. Getting the module boundaries right is the difference between a number a planning officer can use and a number nobody can compare.

Embodied versus operational carbon

Operational carbon is what the meter records: heating, cooling, hot water, lighting, ventilation and the plug loads. It has been regulated for decades through Part L of the Building Regulations and it falls as the electricity grid decarbonises.

Embodied carbon does not fall on its own. It is largely fixed at the moment the concrete is poured and the steel is delivered, and no future grid improvement recovers it. On a new building meeting current fabric standards, the embodied share of lifetime emissions is now the larger part of the total for many building types, which is why planning policy has moved to ask for it.

The practical consequence is a shift in when decisions matter. Structural grid, foundation type, basement extent and whether an existing frame is retained are all settled during concept design, and they set the embodied figure more than any later specification choice.

That is uncomfortable for a design process that traditionally leaves sustainability to a later stage. By the time a services engineer is selecting heat pumps, the carbon that the frame will cost has already been committed. Bringing the assessment forward to concept stage, even as a rough order estimate on quantities from the massing model, is the change that actually reduces emissions rather than merely reporting them.

The lifecycle modules from A1 to D

BS EN 15978 divides the life of a building into stages, and every credible assessment reports against them.

Module D is reported separately and never netted off the total. It is a potential benefit to a future system, and adding it to the headline figure is the most common way an assessment is made to look better than it is. A reviewer checks for that first.

Upfront carbon and why it dominates decisions

Upfront carbon is modules A1 to A5: everything emitted before the building is handed over. It is the figure that policy tends to target, because it is the part you can still change and the part that is emitted now rather than over sixty years.

Substructure and superstructure usually account for the majority of upfront carbon on a new build, which puts the structural engineer at the centre of the exercise rather than the services engineer. Reducing it follows a rough hierarchy: build less, reuse what is there, use less material for the same performance, then substitute lower carbon materials, then optimise transport and site activities.

Concrete deserves specific attention because it is used in such volume. Cement replacement, lower strength classes where the design permits, and reduced slab depths through better structural analysis all move the number. Specifying a headline low carbon mix while retaining a conservative slab thickness usually does not.

Where the RICS methodology sets the rules

The RICS professional standard on whole life carbon assessment for the built environment, second edition, is the reference document for UK practice. It sets the calculation rules, the reporting template, the reference study period, the treatment of sequestration in timber, and the data quality hierarchy that determines whether you may use a generic dataset or must use a product specific environmental product declaration.

Those rules exist so that two assessments of the same building agree. And without them, the choice of dataset alone can move a result by a wide margin. State in the report which edition you followed, the reference study period used, the modules included, the data sources for the main material quantities, and any exclusions. An assessment that omits the exclusions list is not checkable.

A Whole Life Carbon Assessment is one of the report types where councils expect a suitably qualified author and professional review is strongly advised, because the outputs are used to justify demolition and to set carbon reduction targets in conditions.

Retrofit first and the demolition question

The retention question is now asked directly. Where a scheme proposes demolition of a sound existing building, an authority applying a retrofit first policy will want to see the carbon comparison alongside the usual heritage, viability and design arguments.

A defensible comparison sets out the upfront carbon of the new build, the carbon of a retrofit option delivering comparable floor area and performance, and the operational difference over the study period. It also has to state plainly what the retrofit option cannot deliver, whether that is floor to ceiling height, structural capacity, accessibility or the number of homes.

The weakest submissions compare a fully optimised new build against a strawman retrofit. Officers and their advisers have seen enough of these to recognise the pattern. If demolition is the right answer, the comparison will show it.

How London policy asks for the numbers

The London Plan requires whole life-cycle carbon assessments for referable applications, with the Greater London Authority publishing guidance on the template and the reporting stages. Assessments are submitted at planning stage and again post-construction, so the figures you present are checked against what was actually built.

That post-construction step changes behaviour. A planning stage assessment built on optimistic assumptions about cement replacement or steel recycled content becomes a problem when the as-built figures are reported. Where the Energy Statement and the carbon assessment are prepared by different consultants, make sure the same building is described in both, with the same areas, the same structural assumptions and the same services strategy.

Post-construction reporting also creates an evidence trail that a purchaser's technical adviser will ask to see, so keep the model, the quantities and the data sources rather than only the summary report.

Outside London, an increasing number of local plans and supplementary documents ask for embodied carbon information on major schemes. The requirement is not uniform, so check the adopted policy and the validation checklist for the authority rather than assuming.

An illustrative worked example: a five storey residential block with a reinforced concrete frame and a single storey basement. Removing the basement and accepting a smaller plant room, then moving to a hybrid structure above ground, reduces both the A1 to A3 material quantity and the A5 site activity associated with excavation and disposal. The saving comes from the design decision, not from the material specification. This example is illustrative only and any figures for a real scheme must come from a quantified assessment.

This is general guidance, not legal advice, and carbon policy requirements differ between authorities, so check the adopted local plan and validation list 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, and for specialist technical reports, qualified professional input may be required.

Browse the full set of report types on PlanScope if you are scoping the sustainability evidence for a major application.