Calculation appendices in a whole life carbon assessment

Whole life carbon appendices exist so that someone else can check your arithmetic. That is the whole purpose. A reviewer should be able to open the appendix, pick any line in the headline result, and trace it back through a quantity, a carbon factor and a stated assumption to a source they can verify.

Most assessments fail that test for a dull reason. The modelling is fine and the appendix is a PDF of a summary table. If the formulas are gone and the factors are unattributed, the review stops at the first question.

What the appendix has to make checkable

Four things, and they map onto the four ways a reviewer will challenge the result.

The quantities, so that a reviewer can confirm the model reflects the drawings. The carbon factors, so that the source of each emission rate can be identified. The boundary, so that the reviewer can see what was left out and why. And the scenario assumptions, so that the later-life modules can be understood as choices rather than facts.

Everything else in the appendix is supporting material. If those four are present and traceable, the assessment survives scrutiny even where a reviewer disagrees with an assumption, because the disagreement can be quantified.

Module by module reporting

Report against the modular structure in the European standard for assessing the sustainability of construction works, which the professional methodology for whole life carbon assessment follows.

Module D is the one to be careful with. Benefits beyond the system boundary, such as the reuse value of recovered materials, are reported separately and are not deducted from the total. An assessment that nets module D into a headline figure to show a lower number will be sent back, and rightly.

Report results in kilograms of carbon dioxide equivalent per square metre of gross internal area, state the floor area used, and state the reference study period. Sixty years is the conventional period for buildings, and if a different period is used the reason belongs in the appendix.

Quantities take-off and its source

The quantity schedule is the single largest source of error and the easiest thing for a reviewer to check against the drawings.

State where each quantity came from: a model export with the software and model version named, a measured take-off with the drawing numbers and revisions listed, or a cost plan with its date. Where quantities were estimated by rate, say which rate and on what basis.

Then include the schedule itself, as a working spreadsheet with the formulas live. Element, material, quantity, unit, and a cross-reference to the drawing or model element. A reviewer who can select a cell and see the calculation will raise one query. A reviewer who sees a printed number will raise five.

Keep a reconciliation line showing total quantified floor area against the planning drawing schedule. If the two do not match, explain it in the appendix rather than leaving a reviewer to find a discrepancy.

Carbon factors and product data

Each factor needs three pieces of information: the value, the source, and whether it is generic or product specific.

Environmental product declarations, verified to the relevant European standard, are the preferred source for product stage emissions. Where one exists for the specified product, use it and cite the declaration number and its date. Where it does not, use a recognised industry dataset and say which version, because these are revised and a factor from an older edition can differ materially.

Three practical points. Declaration data has a validity period, so a declaration that has expired should be flagged. Factors expressed per tonne and per cubic metre are easy to confuse, and the unit conversion belongs in the spreadsheet rather than in someone's head. And a factor for a product with a specified recycled content applies only if that content is actually specified, so the appendix should cross-refer to the specification clause.

Where the assessment feeds a Circular Economy Statement, the reuse and recycled content assumptions have to be consistent across both documents, and inconsistency between them is a familiar line of challenge.

Assessment boundary and exclusions

State the boundary positively, then state the exclusions as a list with a reason for each.

A typical boundary statement covers the building or buildings assessed, the external works included, whether below-ground structure and remediation are inside the boundary, whether demolition of existing structures is included and under which module, and whether fit-out and loose furniture are in or out.

The exclusions list should name each omitted element and give the reason, whether that is a lack of data, immateriality, or a convention in the methodology. An exclusion with a stated reason is a judgement a reviewer can accept or query. An unstated exclusion reads as an omission.

Where an existing building is being demolished, that demolition carbon is one of the most contested numbers in the assessment, and a Pre-redevelopment Audit recording what is on site and what can be reused gives the demolition and reuse assumptions an evidence base. The related note on pre-redevelopment audit content for material reuse goes into what that audit should record.

Scenario assumptions for later life modules

Modules B and C are scenarios, not measurements, and the appendix should present them as such.

Set out, in a table, each assumption and its basis: the replacement interval assumed for each major element, the maintenance regime, the end-of-life route assumed for each material with the recovery rate, and the grid decarbonisation trajectory applied to operational energy in module B6.

The grid trajectory is where results move most. A projection that assumes rapid decarbonisation reduces modelled operational carbon substantially across a sixty year period, so name the projection, name its publisher and its vintage, and run a sensitivity case with a slower trajectory. Reviewers in London in particular will ask.

Replacement intervals deserve the same treatment. An assumption that a facade system lasts the full study period without replacement is a claim, and it should be stated as one.

File formats a reviewer can open

This is mundane and it decides whether the appendix works.

Supply the calculation as a spreadsheet with live formulas, in a format that opens without specialist software. Where the authority publishes a reporting template, use the template and supply it completed rather than converting the output into your own format. Provide the quantity schedule and the factor library as separate tabs or files rather than embedded images. Name files so that a version is identifiable.

What does not work: a locked spreadsheet, a PDF print of a dashboard, a proprietary model file with no export, or a summary that reports only the total. All four produce the same response, which is a request for the information you should have supplied.

A PlanScope Whole Life Carbon Assessment draft can structure the reporting, set out the module framework and the assumptions table, and flag each figure that needs a sourced input, inserting a marker rather than inventing a factor. The calculation itself needs a suitably qualified assessor, and councils expect one, so professional review is strongly advised before submission.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.