Retrofit or demolish: making the embodied carbon case at planning

The retrofit first embodied carbon planning argument is now decided on an options appraisal rather than on assertion. If your scheme involves demolishing an existing building, expect the authority to ask why retention was not possible, and expect the answer to be judged on whole life carbon evidence covering both the embodied carbon locked into the existing structure and the operational performance of each option. London applies this most formally, and authorities outside London increasingly ask the same question through design and sustainability policies.

The practical consequence is that the appraisal has to exist before the design is committed. An options study produced after the demolition drawings are complete reads as a justification exercise, and officers recognise one when they see it.

Where the expectation comes from

Three strands converge. National policy supports making effective use of land and existing buildings, and the current National Planning Policy Framework, published on 17 August 2026 with policy-coded chapters, carries design and climate policies that authorities cite in support of retention. Verify the relevant policy codes against the published Framework at the time you write, because the coding replaced the older paragraph numbering.

The second strand is local. The London Plan requires whole life carbon assessment and circular economy reporting for referable schemes, and boroughs apply the guidance the Greater London Authority publishes. Several authorities outside London have adopted local plan policies with a similar effect.

The third is professional. The RICS Whole Life Carbon Assessment for the Built Environment, second edition 2023, provides the method most assessments now follow, and using a recognised method is what makes a comparison arguable. An appraisal built on a bespoke spreadsheet with undisclosed assumptions persuades nobody.

Comparing options on a like for like basis

The comparison has to be fair, and most weak appraisals fail here rather than on the arithmetic.

• Same assessment boundary for every option, stated explicitly by life cycle module
• Same study period, normally 60 years, applied consistently
• Same functional unit, whether that is floor area, bed spaces or occupancy
• Same grid decarbonisation assumptions across all options
• Same treatment of maintenance and replacement cycles
• Same end of life assumptions

The awkward case is where retention delivers less floor area than redevelopment. Comparing a retained 4,000 m² building against a new 6,000 m² one on total carbon flatters retention, and comparing them per square metre flatters the new build. The honest approach is to present both, say which comparison you consider decisive and why, and let the officer see the working. Hiding the mismatch in a single normalised figure is the error most likely to be spotted.

At least three options should be tested: full retention and refurbishment, partial retention with extension, and demolition and rebuild. Two-option appraisals read as binary choices that were never open.

Structural condition evidence that carries weight

The commonest reason given for demolition is that the existing structure cannot take the loads or the layout the scheme needs. Sometimes true. Often untested.

What carries weight is a structural appraisal from a chartered engineer that states what was inspected, what was opened up, what testing was done and what the residual capacity is. What carries little weight is a paragraph asserting that the frame is inadequate. Officers in authorities that take this seriously now ask for the intrusive survey, and a Structural Survey that has looked inside the fabric is worth considerably more than a visual walkover.

Three findings do support demolition when properly evidenced: contamination or deleterious materials whose removal requires dismantling, floor to floor heights that cannot accommodate the required servicing even with a reduced strategy, and structural capacity that cannot be upgraded at proportionate cost and carbon. Note the last one has a carbon test as well as a cost test, because strengthening interventions carry their own embodied carbon and sometimes lose the argument on their own terms.

A pre-redevelopment audit of materials in the existing building supports both the carbon case and any reuse strategy, and the related circular economy comparison is worth reading alongside the structural work.

Operational and embodied carbon together

Retention usually wins on embodied carbon and loses on operational carbon, at least against a new building designed to current standards. The appraisal has to show both, over the study period, and the crossover point is the number that decides the case.

Two factors have moved that crossover in recent years. Grid decarbonisation reduces the operational penalty of a less efficient envelope, because the carbon per kilowatt hour keeps falling. And deep retrofit has improved, so the performance gap between a well-retrofitted existing building and a new one is narrower than it was.

State the grid carbon factors used and their source, and apply the same projection to every option. An appraisal using a fixed present-day factor across 60 years overstates the operational penalty of retention, and a reviewer will say so.

Heritage and viability in the balance

Where the building is listed or in a conservation area, the statutory duties under the Planning (Listed Buildings and Conservation Areas) Act 1990 apply and the heritage balance is separate from the carbon balance. A Heritage Statement addressing significance and harm has to sit alongside the carbon work, and where the two point the same way the case is strong.

Viability is the weaker argument and the more scrutinised. An assertion that retention is unviable needs an appraisal prepared to the Planning Practice Guidance on viability, and authorities publish it for consultation in many cases. Running a viability argument on retention means accepting that level of scrutiny.

The honest position, and one worth stating in the submission, is that retention often costs more per square metre and produces less lettable area, and that this is a real constraint rather than a reluctance. Officers respond better to that than to an argument that retention is technically impossible when it plainly is not.

Presenting an appraisal officers accept

1. State the question: which option delivers the scheme's requirements at the lowest whole life carbon.
2. Describe the existing building, its condition and the evidence base for that description.
3. Set out the options tested, including the ones rejected at concept stage and why.
4. Present the carbon results by life cycle module for each option, with the method, boundary, study period and factors stated.
5. Present cost and floor area alongside carbon, so the trade-off is visible rather than implied.
6. Reach a conclusion that follows from the numbers, and identify what would change it.

The results belong in the Whole Life Carbon Assessment, with the design reasoning carried through into the design and access statement rather than repeated separately.

When the numbers favour demolition

They sometimes do, and an appraisal that always concludes in favour of the client's preference is not an appraisal. Where demolition wins, the submission should say what the scheme does to mitigate the loss: material reuse on site, off-site reuse of recovered components, reduced structural quantities in the new building, low carbon concrete specification, and a design life that justifies the investment.

Officers are readier to accept demolition from an applicant who has shown the retention case fairly and lost it than from one who never ran it. That is the practical reason to do this work early, and the reason a late options appraisal rarely changes an officer's mind.

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 and structural appraisals are normally expected to be authored by suitably qualified professionals, 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.