The baseline problem in a refurbishment carbon assessment

A whole life carbon refurbishment assessment fails review more often on its baseline than on its arithmetic. The standard reporting template assumes a new building on a cleared site, where modules A1 to A5 capture everything that goes into it. A refurbishment starts with a structure that already exists, was built decades ago and carries no product-stage carbon within the assessment boundary. Decide how you are treating that structure, say so in the first page, and half the reviewer's objections disappear.

The rest of this is about the decisions you have to make and the ones you have to defend.

Why the standard template does not fit

Whole life carbon reporting follows the modular structure familiar from the European standard on building sustainability: product and construction stages, use stage, end of life, and benefits beyond the system boundary.

For a new build, every element passes through A1 to A3. For a refurbishment, the retained frame, foundations and often the facade do not. They were manufactured and installed long before the assessment period begins, and the accepted convention is that their product and construction stage carbon sits outside the boundary.

That convention produces a number that looks extraordinary. A deep retrofit can report an upfront figure a fraction of the equivalent new build, and a reviewer who has seen fifty new build assessments will assume an error. The answer is to state the boundary in plain terms at the front of the report, with the retained elements listed, rather than leaving it to be inferred from an appendix.

Treating retained structure properly

Excluded from the product stage does not mean excluded from the assessment.

Retained elements still carry end of life carbon at the close of the study period, so they appear in modules C1 to C4. They carry maintenance, repair and replacement over the period, so they appear in modules B1 to B5. And anything done to them now, including strip-out, local demolition, structural strengthening and making good, is new work with its own product and construction stage carbon.

Strip-out is the item most often missed. Removing partitions, services, finishes and part of a facade generates transport and waste processing carbon that belongs in the construction stage, and on a heavy commercial retrofit it is not a rounding error. An assessment that shows a refurbishment with almost no construction stage carbon has usually forgotten it.

List the retained elements, the elements being removed and the new elements in three columns. Reviewers read that table before they read anything else.

Choosing a comparison baseline

Here is the part where practitioners disagree, and where I would rather state an opinion than pretend there is a settled answer.

There are three candidate baselines. Do nothing, which is honest but useless because the building does not meet the brief. Demolish and rebuild to the same area and specification, which is the comparison planning committees actually want. And a notional compliant new build, which is what most benchmark data describes.

The defensible approach is to report the refurbishment absolutely, by module and in kgCO2e per m² of gross internal area, and then present the demolish-and-rebuild comparison separately as a clearly labelled sensitivity. Do not blend them. A single headline saving figure that quietly embeds a counterfactual is the thing that gets picked apart.

If you are presenting the comparison, say what the notional new build is: same area, same use, same storey height, current Building Regulations compliance, and whether the demolition of the existing structure is included in it. It should be, and including it is usually what makes the refurbishment case.

Benchmarks that apply, and those that do not

Published benchmarks for upfront embodied carbon are overwhelmingly derived from new build projects. Applying them to a refurbishment and reporting compliance is close to meaningless, because the boundary differs.

Two more useful moves. Report the refurbishment against its own new build counterfactual, calculated on the same basis by the same assessor. And report the operational element, module B6, against the relevant standard, because that comparison is like for like and is often where a retrofit looks weakest.

Where a scheme sits in London and is referable, the Greater London Authority's whole life carbon guidance sets out the reporting format and the benchmarks expected, and the circular economy requirements run alongside. Check the current guidance rather than a version saved two years ago, since the templates have been revised.

Replacement cycles in an old building

Module B4 is where refurbishment assessments quietly go wrong in the other direction.

Reference service lives are published for new components. A retained window, roof covering or cladding panel installed in 1978 does not have a full service life ahead of it. If the study period is 60 years and a retained flat roof has perhaps eight years left, the assessment needs two replacements in that period rather than one.

Be explicit. Tabulate each retained component, its estimated remaining service life, the assumed replacement interval and the source of the assumption. A condition survey is the right evidence base, and where one exists it should be cited. Assuming that everything retained behaves like a new component is the single most common way a refurbishment assessment overstates its case.

The same discipline applies to services. Retained plant rarely survives a 60 year period without full replacement, and B6 depends on what is installed after that replacement.

Presenting the saving credibly

Four things make the report persuasive to a case officer who is not a carbon specialist.

1. A boundary statement in plain language on the first page, naming what is retained and why it sits outside the product stage.
2. Results by module, in a table, in kgCO2e/m² gross internal area, with the total for the study period and the upfront figure shown separately.
3. The counterfactual as a labelled sensitivity, with its own assumptions stated.
4. A short note on what would change the answer, such as the structural capacity of the retained frame or the condition of the facade.

Avoid the single dramatic percentage. It invites a challenge you cannot fully answer, and the underlying case is strong enough without it.

The Whole Life Carbon Assessment should also be consistent with the operational case. If the Energy Statement assumes a fabric upgrade that the carbon assessment has not costed in embodied terms, the inconsistency will be spotted.

Criticisms reviewers make, in order of frequency

The boundary for retained elements is unstated or inconsistent between the narrative and the model. Strip-out and local demolition are omitted from the construction stage. Retained components are given full reference service lives. The comparison baseline is undefined or shifts between sections. New build benchmarks are applied to a refurbishment figure. Floor area definitions differ between the carbon report and the planning drawings.

That last one sounds trivial and is not. A gross internal area taken from an early scheme and never updated makes every per-square-metre figure in the report wrong.

Where the existing building is listed or in a conservation area, the fabric measures available are constrained in ways the carbon model has to respect, which is the problem set out in external wall insulation in a conservation area. And the structural argument for retention sits alongside the material choices discussed in modern methods of construction and the carbon case.

Councils normally expect whole life carbon work from a suitably qualified assessor, and professional review before submission is strongly advised.

Browse the 66 PlanScope report types to see how the carbon, energy and circular economy documents fit together in a submission.

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.