Whole life carbon assessment outline, module by module

A whole life carbon assessment outline is dictated by the module structure of BS EN 15978, and an assessment that reorganises those modules into its own headings is the single most common reason officers send one back. Report module by module, in order, with the same units throughout, and state clearly which modules are excluded and why. That is most of the battle.

The document that follows is not a design narrative. It is a results report with an audit trail, and its readers are a sustainability officer checking coverage and a consultant checking arithmetic. Write for them.

Scope, boundary and assessment stage

Open with the facts that let a reader interpret every number that follows. State the gross internal area in square metres and say how it was measured. State the reference study period, conventionally 60 years for buildings. State the design stage at which the assessment was carried out, because a stage 2 assessment based on outline quantities carries different uncertainty from a stage 4 one built on a measured bill.

Then define the physical boundary. Say whether external works, landscaping, site infrastructure, basements, temporary works and tenant fit-out are inside or outside the assessment. Say how existing structure being retained is treated. If the scheme has several blocks or phases, say whether the figure is aggregated or reported per block.

Units must be fixed here and never varied: kgCO2e for absolute figures and kgCO2e per square metre of gross internal area for normalised ones. A report that mixes tonnes and kilogrammes between tables invites a query that costs a fortnight.

Modules reported and modules excluded

Set out a coverage table before any results. One row per module, one column stating included or excluded, one column giving the reason. It takes half a page and it prevents most officer questions.

Module D is where reports go wrong. Reuse and recycling potential belongs in D, reported on its own line, and it must not be subtracted from the A to C total to produce a headline figure. The same discipline applies to biogenic carbon in timber: sequestration is recorded in the product stage and reversed at end of life, so a report showing the negative without the corresponding release is incomplete.

Data sources and how to describe their quality

Every quantity in the assessment comes from somewhere, and the report has to say where. Use a short hierarchy and apply it consistently: verified product-specific environmental product declarations first, then sector average declarations, then recognised generic datasets.

For each major material, record the source, the declaration number or dataset version where one exists, the declared unit and the date. Where a generic figure has been used because the product is not yet specified, say so in the row rather than in a footnote. A table of twelve materials with honest provenance is worth more than a claim that the assessment used the best available data.

Quantities need the same treatment. State whether they came from a measured schedule, a model take-off or a rate applied to floor area, and give the allowance made for wastage. Uncertainty at stage 2 is normal and declaring it protects the assessment from the accusation of false precision later.

Substructure and superstructure results

Break the embodied results down by building element using a recognised element classification rather than trade packages. Substructure, frame, upper floors, roof, stairs, external walls, windows and doors, internal walls, internal finishes, fittings, services. Give each element its A1 to A5 figure in absolute and normalised form and its percentage share.

This is the section a design team actually uses. It shows whether the answer lies in the frame, the substructure or the facade, and it makes the case for the design changes described later. On a concrete-framed residential block the frame and substructure together usually dominate the A1 to A5 total, and the report should say so plainly rather than treating all elements as equally worth optimising.

Where the scheme retains existing structure, show the retained element as an avoided quantity in the narrative and keep it out of the reported A1 to A3 figure, with the retained fabric's repair and strengthening works counted in.

In use and end of life modules

B4 replacement is the module that carries the most assumptions and gets the least scrutiny. List the service life assumed for each replaceable component, name the source for that service life, and show the number of replacement cycles within the reference study period. A facade cladding system with a 30 year life in a 60 year study period is replaced once, and the difference between assuming 30 and 40 years changes the result materially.

B6 operational energy should be reported from the same model used for the energy strategy, with the carbon factor and its source stated, and the projection basis for grid decarbonisation described. Keep it separate from the embodied total. A Whole Life Carbon Assessment that merges B6 into a single lifetime figure without showing the split cannot be compared against any published benchmark.

End of life modules rest on assumed future practice, so state the assumed treatment route for each material group and the data source for it. Do not present C module results as precise.

Benchmarks and what comparison is worth

Compare against published benchmarks for the building type and say which edition you used, because the Greater London Authority guidance on whole life-cycle carbon and the reporting standards behind it have both been revised. Give the benchmark, the scheme figure and the gap, in the same modules and the same units. A comparison against a benchmark covering A1 to A5 using a figure that includes B and C modules is meaningless, and officers now check.

For London referable schemes the assessment sits alongside the Circular Economy Statement and the Energy Statement, and the three should share quantities and assumptions. Nothing undermines a submission faster than three documents giving three different floor areas.

Reductions achieved and reductions rejected

Close the report with a reduction narrative that has numbers attached. For each measure adopted, state the modules affected and the saving in kgCO2e per square metre. For each measure considered and rejected, say why, whether on cost, buildability, fire performance or programme. Officers read the rejected list carefully, and an honest one is more persuasive than a page of measures with no quantities.

Then state what remains and what will be done at the next stage, including any commitment to a post-construction assessment. Where a condition or obligation requires a post-construction submission, say which template will be used and against which figures the comparison will be made.

An illustrative example: on a five storey residential block assessed at stage 3, substructure and frame accounted for the bulk of A1 to A5, a cement replacement specification took a share out of A1 to A3, and reducing the basement footprint removed more carbon than every finishes change combined. Figures of that kind are scheme-specific and the pattern should be tested, not assumed.

The same schedule discipline applies to other evidence documents, and the approach to laying out assumptions is set out in the note on a viability appraisal inputs schedule. To see how a carbon assessment sits within the wider document set, browse the 66 report types by category.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional 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. For specialist technical reports, qualified professional input may be required.