Whole life carbon modules A to C explained

A whole life carbon figure means nothing until you know which modules it covers. Two assessments of the same building can differ by a factor of two because one stops at practical completion and the other runs to demolition and disposal sixty years later. The modules are the scope, and stating them is the first job of the assessment.

The module structure comes from the European standard for assessing the sustainability of construction works, which the RICS professional standard on whole life carbon applies in a UK context. Modules are lettered by life cycle stage: A for product and construction, B for use, C for end of life, and D for benefits and loads beyond the system boundary.

What each module covers

The breakdown is worth memorising, because every conversation about carbon scope uses it.

Embodied carbon is usually taken to mean modules A1 to A5 plus B1 to B5 plus C1 to C4. Whole life carbon adds the operational modules. Module D is reported separately and is never netted off the total, because it describes benefits that fall outside the building's own life cycle.

Product and construction stages in practice

A1 to A3 dominate most assessments, commonly accounting for the majority of embodied carbon in a new building. Structure and substructure typically carry the largest share, which is why the structural option appraisal is where carbon reduction is actually delivered rather than in specification tweaks at the end.

A4 is small in comparison, though it becomes material for heavy, low-value materials moved long distances. Aggregates and precast concrete are the usual examples. Recording actual sourcing distances rather than default assumptions is worth doing where a local supply chain is part of the argument.

A5 covers site energy, plant, temporary works, waste arising during construction and, in the current RICS approach, pre-construction demolition. That last inclusion changes the answer for redevelopment schemes and is one reason retention options score better than they used to. Where an existing building is being taken down, a pre-redevelopment audit identifying what can be reused or recovered feeds directly into both the A5 figure and any circular economy commitments.

In use emissions and replacement cycles

The B modules are where assumptions do the heavy lifting, and where two competent assessors can produce different answers in good faith.

Replacement cycles under B4 depend on assumed service lives. A facade system assumed to last 60 years is never replaced within the study period. The same system assumed to last 30 years is replaced once, and its A1 to A3 carbon is counted twice. Publish the service life assumptions in a table, because a reviewer cannot check the result without them.

B6 is operational energy, and it should be consistent with the energy assessment submitted alongside. Where the energy statement models one heating strategy and the carbon assessment assumes another, the inconsistency is the first thing a reviewer will find. Carbon factors for grid electricity change over the study period, and the assessment should say whether a decarbonisation trajectory has been applied and on what basis.

B1 catches refrigerant leakage from heat pumps and cooling systems, which is easy to overlook and can be substantial where high global warming potential refrigerants are specified. Low GWP refrigerant selection is a real carbon decision, not a compliance detail.

End of life and the beyond boundary module

C1 to C4 cover taking the building apart, transporting the material, processing it and disposing of what cannot be recovered. The figures rest on assumptions about future waste treatment that nobody can verify, which is why they are usually modelled from standard datasets rather than project data.

Module D is the one most often misused. It reports the potential benefit of materials being reused or recycled after the building's life, and of energy exported from the site. Because those benefits accrue to a future system rather than to this building, the standard requires them to be reported separately. An assessment that subtracts module D to reach a headline figure has overstated the result, and a reviewer will ask for the total without it.

Design for deconstruction improves module D and is worth describing in the narrative: mechanical fixings rather than adhesives, bolted rather than welded connections, avoidance of composite materials that cannot be separated, and a materials passport. Those choices also support the commitments in a circular economy statement where one is required.

Data sources and their quality hierarchy

Not all carbon data is equal, and the assessment should state which tier each material used.

1. Product-specific environmental product declarations, verified to the relevant standard, for the products actually specified.
2. Manufacturer average declarations covering a range of products from one manufacturer.
3. Industry average or sector declarations.
4. Generic database figures.

Early in design, generic data is appropriate and honest. At the point of a planning submission, the more the assessment relies on generic figures, the less weight it carries, particularly for the structure. Where a product-specific declaration has been used for a material that later changes at procurement, the figure changes with it, which is an argument for conservative assumptions rather than best-case ones.

State the database version and the date. Carbon factors are revised, and an assessment quoting a figure without a source cannot be checked.

Reporting format an officer can read

Officers assessing a whole life carbon assessment are typically looking for four things: the scope, the result against a benchmark, the reduction measures adopted, and the assumptions that could change the answer.

Present results in kg CO2 equivalent per square metre of gross internal area, broken down by module and by building element, over a stated reference study period, normally 60 years for a building. Include the total with and without module D. State the gross internal area used and reconcile it with the accommodation schedule.

Where the London Plan applies, follow the Greater London Authority's whole life-cycle carbon assessment guidance and its reporting template, which sets the required modules, benchmarks and the pre- and post-construction reporting stages. Check the current version, because the template and the benchmarks have been updated since the plan was adopted.

Assumptions that change the answer most

If you have limited time to interrogate an assessment, these are the inputs to test.

The structural option, because structure and substructure usually dominate A1 to A3. The assumed service lives driving B4 replacements. The gross internal area used as the denominator, which can flatter a result if measured generously. The treatment of module D. The concrete specification, particularly cement replacement levels and whether the assumed mix is achievable for the programme. The reuse assumptions for any retained structure, which need survey evidence rather than optimism. And the decarbonisation trajectory applied to grid electricity in B6.

Change any one of those and the headline figure moves. That is not a weakness of the method, but it does mean an assessment without a stated assumption set is a number rather than an analysis. Ask for the assumptions before you ask for the result.

Whole life carbon assessments are normally expected to be prepared by a suitably qualified assessor working to the current RICS professional standard, and professional review is strongly advised before submission.

PlanScope drafts sustainability and carbon documents structured to UK planning policy, with modelled figures and assumptions flagged for your assessor to supply. Browse the report types and start a draft. Reports should be reviewed before submission, and we do not guarantee planning approval.