Evidencing an embodied carbon target in a local plan policy

Where a local plan policy sets a numeric embodied carbon target, the number is almost always expressed in kilogrammes of carbon dioxide equivalent per square metre of gross internal area, covering modules A1 to A5 of the life cycle. Demonstrating compliance means producing a whole life carbon assessment to a recognised methodology, reporting the result against that figure, and then committing to report again once the design is fixed. The policy sets the target. The structural scheme decides whether you hit it.

Where the target comes from

Embodied carbon targets have arrived in local plans by two routes. Some authorities set a numeric figure in a development management policy, usually applying above a floorspace or unit threshold. Others require an assessment and a reduction against a stated benchmark without naming an absolute limit.

Read the policy and the supporting text together, because the supporting text normally tells you which methodology, which modules and which benchmark document the authority has in mind. A policy that says "whole life carbon" and supporting text that references upfront embodied carbon only are asking different questions, and submitting the wrong scope wastes a round of consultation.

Take the number from the policy, not from a national target. The figures in sector guidance, in London's whole life-cycle carbon guidance and in the design profession's own challenge targets are not interchangeable, and they are not all measured on the same basis.

Units, modules and what is actually being measured

The module structure comes from BS EN 15978 and it matters because policies cut it at different points.

Upfront embodied carbon means A1 to A5. A whole life figure means A to C, with module D reported alongside rather than subtracted. The commonest error in submitted assessments is netting module D off the total to hit the target, which assessors spot immediately.

The methodology to use is the RICS whole life carbon assessment standard, second edition, which sets the calculation rules, the data hierarchy and the reporting template. A Whole Life Carbon Assessment prepared to that standard, with the reporting template completed, is what an authority can actually review. One prepared to a bespoke spreadsheet with undocumented factors is not.

Which design decisions move the number

Upfront embodied carbon on a new build is dominated by structure and substructure. On a typical frame building, the superstructure frame, the floors and the foundations together account for the large majority of modules A1 to A5, which is why facade tinkering and specification swaps late in the design produce disappointingly small savings.

The levers that work, roughly in order of effect:

1. Retain and reuse existing structure. Nothing else comes close. A retrofit with a new facade and new services will usually beat a new build on upfront carbon by a wide margin.
2. Avoid or reduce the basement. Excavation, retaining walls and piling are carbon intensive and deliver low value floor area.
3. Rationalise the grid and the spans. Long spans need deeper sections and more material in both the frame and the foundations.
4. Specify cement replacement in concrete, and set the replacement level in the structural specification rather than hoping the contractor offers it.
5. Reduce floor build-ups and finishes, which have short replacement cycles and therefore recur in the B modules.
6. Use lower carbon steel and reused steel where the supply chain can evidence it.

Our note on thermal bridging detail at planning stage makes the related point that envelope decisions made at planning bind the operational performance. Embodied carbon works the same way, except the binding decision is the engineer's, not the architect's.

Reporting at planning and again later

Most policies ask for two assessments. The first accompanies the application and reports the design as submitted. The second follows once the design is developed or the building is complete, and reports what was actually specified and built.

Expect the second to be secured by condition or by obligation, with a trigger tied to practical completion or to a defined period after it. Check the trigger before you accept the wording, because a requirement to report within three months of completion lands at the busiest possible moment and the quantity data is often still being reconciled.

The two assessments need to be comparable. Use the same boundary, the same area measurement, the same module scope and the same reporting template. Where the design has changed, explain the change rather than restating a new baseline, because an authority comparing two incompatible assessments will assume the worse of the two is the true one.

When the target cannot be met

Sometimes it cannot, and the honest submission says so with reasons.

The cases that recur are deep basements driven by a site constraint, long spans driven by a required column-free use, piled foundations driven by ground conditions, and transfer structures driven by a required mix of uses. Each of those is a carbon cost imposed by something other than a design preference.

What persuades an authority is the counterfactual. Show the options you tested, the carbon of each, and why the chosen option was taken. Show the measures adopted to reduce what remains. And show the figure you can commit to, which may be above the policy target but below the benchmark the policy was written against.

What does not persuade is a statement that the target is aspirational. Some policies are drafted that way and some are not, and an assessor will read the wording more carefully than the applicant did.

Conditions and obligations used to secure the outcome

Three mechanisms appear, and they differ in how much risk they leave with you.

A condition requiring a post-completion assessment to be submitted is the lightest. It secures reporting rather than performance, so a shortfall is evidenced rather than penalised. A condition requiring the development to be constructed so as not to exceed a stated figure is far heavier, because it makes a quantity surveyor's reconciliation into a compliance question. And an obligation requiring a payment where the target is exceeded puts a price on the shortfall, which some authorities now use.

Negotiate for reporting plus a commitment to the measures, rather than an absolute numeric cap, unless you are confident of the structural scheme. A Sustainability Statement is the right place to set out which measures are being committed to and how they will be evidenced, alongside the carbon assessment itself. Where the same policy also requires a rating, the credits in a BREEAM pre-assessment that deal with material life cycle impacts should be scored off the same assessment rather than separately.

Keeping the assessment and the structural design aligned

The assessment is only as good as its quantities, and the quantities belong to the engineer and the cost consultant rather than to the assessor.

So agree a single source for areas, a single structural model revision, and a single materials schedule, and date-stamp all three. Where product specific environmental product declarations are being used, keep copies, because an assessor will ask for the ones that drive the largest line items. Where generic data is used, say which database and which version.

As an illustrative example, a seven storey office scheme reporting 780 kgCO2e/m² at planning on a reinforced concrete frame with a single basement level might find the figure rising to 840 at technical design because the piling design changed after the ground investigation. If the condition requires reporting, that is a letter. If the condition caps the figure, it is a section 73 application and a renegotiation.

Set the carbon target conversation with the structural engineer before the planning drawings are frozen. After that point the number is largely decided and the assessment is just arithmetic. This is general guidance rather than legal advice, and for specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.