Whole life carbon: what modules A to D actually cover

Whole life carbon modules a to d are the accounting frame for a building's emissions, borrowed from the European standard on sustainability assessment and adopted by the RICS methodology that most UK planning submissions follow. Modules A cover getting the building built. B covers keeping it running. C covers taking it down. D sits outside the total altogether, which is the part that causes most of the arguments.

Get the module boundaries right and two assessments of the same building become comparable. Get them wrong and the headline figure is meaningless.

The module structure

A1 to A3 is the product stage: extracting raw materials, transporting them to the factory and manufacturing the components. A4 is transport from factory gate to site. A5 covers the construction process itself, including site energy, temporary works and the carbon in construction waste.

B1 to B7 is the use stage. B1 is emissions from materials in use, B2 maintenance, B3 repair, B4 replacement, B5 refurbishment, B6 operational energy and B7 operational water. The RICS methodology adds a module for users' use of infrastructure.

C1 to C4 is end of life: deconstruction and demolition, transport, waste processing and final disposal.

D is separate by design. It reports benefits and loads beyond the system boundary, such as the value of materials that can be recycled or reused after demolition, and energy exported from the site.

Three shorthand terms follow from this. Upfront carbon is A1 to A5, the emissions already released by the time the building opens. Embodied carbon is A1 to A5 plus B1 to B5 plus C1 to C4. Whole life carbon is everything, operational energy and water included.

Upfront carbon and why it dominates

For a new building meeting current energy standards, upfront carbon is usually the largest single portion of the whole life figure, and it is spent before a single occupant arrives.

That has a consequence for planning. Operational improvements pay back over decades. Upfront emissions are irreversible at the point of construction, which is why policy attention has moved towards the substructure, the frame and the facade, where most of the mass sits.

It is also why retention arguments carry weight. Keeping an existing frame avoids most of the A1 to A3 emissions of a replacement, and the assessment should model retention as a genuine option rather than presenting demolition as a given. A Pre-redevelopment Audit that records what is in the existing building and what could be reused gives the reuse case something to stand on.

In use and maintenance modules

B2 to B5 depend entirely on replacement cycles, and replacement cycles are assumptions. A facade sealant assumed to last 25 years against a 60 year study period is replaced twice. Assume 30 years and it is replaced once. The difference across a whole building can be large.

State the service life assumed for each element and where the figure came from. Manufacturer data, published service life tables and professional judgement are all acceptable sources, but an assessment that gives no sources cannot be checked.

B6 and B7 connect to the energy work. Operational energy in the whole life assessment should be consistent with the Energy Statement rather than derived separately, and where the two documents disagree the reviewer will notice. Use the same model outputs and say which carbon factors were applied, including any assumed decarbonisation of the grid over the study period.

Grid decarbonisation assumptions deserve a sentence of their own. A study that assumes rapid decarbonisation reduces B6 substantially and shifts the balance towards embodied carbon. That is defensible, but it should be stated rather than buried in a spreadsheet.

End of life and the treatment of module D

C1 to C4 are modelled on scenarios, because nobody knows how a building will be demolished in sixty years. Use the standard scenarios the methodology sets out and say which were used.

Module D is the one to handle carefully. It captures the potential benefit of materials being recycled or reused beyond the building's life, and it can be a large negative number. It is reported separately and is not netted off the whole life total.

Assessments that present a headline figure with module D already deducted are not comparable with anything, and reviewers challenge them. A steel-framed building can look better than a timber one on that basis, which tells you the presentation is doing the work rather than the design.

Biogenic carbon in timber needs the same discipline. Sequestration is reported at the product stage and the corresponding emission is reported at end of life, so a timber building shows a benefit early and a cost late. Reporting only the first half is not an assessment.

Benchmarks and how to cite them

Planning policy that requires a whole life carbon assessment usually also sets a benchmark or an aspirational target, most commonly expressed as kilograms of carbon dioxide equivalent per square metre of gross internal area for modules A1 to A5.

In London, the London Plan requires whole life carbon assessments for referable applications and the Greater London Authority publishes guidance with benchmark and aspirational figures by building type, plus a reporting template. Take the numbers from the current guidance rather than from a previous scheme, because both the template and the figures have been revised.

Industry design guides publish banded targets that some councils reference outside London. Cite the source, the version and the building type, and state whether the figure is a benchmark to meet or an aspiration to work towards. A Whole Life Carbon Assessment that quotes a target without saying which document it came from invites a request for clarification.

Scope decisions that change the answer

Six decisions move the result more than any design change.

1. The study period, conventionally 60 years, which sets how many replacement cycles fall inside the assessment.
2. The floor area definition used for normalisation, and whether basements and external works are included in it.
3. Which building elements are in scope, particularly external works, landscaping and fit-out.
4. Whether operational modules are included in the headline or reported separately.
5. The proportion of material covered by product-specific environmental declarations rather than generic data.
6. The treatment of biogenic carbon and module D.

Two assessments that differ on any of these are not comparable, and a reviewer comparing a scheme against a benchmark has to know the answers. Put them on the first page.

Presenting results a reviewer can check

A usable submission has a module-by-module table in the RICS format, a normalised figure per square metre with the area definition stated, the study period, the data sources with the share of mass covered by product-specific declarations, the exclusions, and a short section on what the design did to reduce the figure.

Include the comparison that matters: the assessed design against the benchmark, and against at least one alternative the team considered. An assessment that reports a single number with no counterfactual tells a planning officer nothing about whether the design responded to it.

Where the scheme also needs a Circular Economy Statement, keep the material quantities consistent between the two. They are drawn from the same bill of quantities and a discrepancy between them is the first thing a reviewer spots.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Whole life carbon assessment is work councils expect a suitably qualified author to carry out, and professional review is strongly advised. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

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