Retaining existing structure rather than demolishing
Where a council applies a retrofit first expectation, the application turns on an options appraisal comparing retention and demolition on the same basis. The structural testing has to come first.
Retrofit first planning policy is not a national requirement in England, and on a growing number of schemes it decides the application anyway. Where it applies, the council expects an options appraisal that compares retention, partial retention and demolition on structural feasibility and embodied carbon, and it expects the comparison to be done before the design is fixed rather than justified afterwards. The evidence sits in a structural appraisal, a whole life carbon comparison and a pre demolition audit. Get the sequence wrong and you are defending a demolition you have already designed.
Where the expectation comes from
There is no national policy that says retain before you demolish. The pressure comes from three directions.
In London, the London Plan requires referable applications to submit whole life carbon assessments and circular economy statements, and its design policies ask applicants to demonstrate that the proposal makes the best use of the site, which in practice invites the retention question. A number of boroughs have gone further in their own local plans and supplementary documents, setting an explicit expectation that retention is tested first.
Outside London the driver is usually a local plan climate policy, a design code, or a heritage policy where the building is locally listed or contributes to a conservation area. Some authorities apply it through a design review panel rather than a written policy, which is harder to plan for because the expectation is not written down anywhere you can quote.
The third driver is the planning balance itself. Once an officer has read that demolishing and rebuilding releases substantially more embodied carbon than adapting the existing frame, that finding becomes a material consideration whether or not a policy compels the analysis.
The options appraisal councils expect
An options appraisal that lists two choices, retain or demolish, and concludes demolition, will be read as a formality. Three or four options with a consistent basis of comparison reads as an assessment.
The options normally worth testing are full retention with internal remodelling, retention of frame and core with new facade, retention of substructure and lower floors with new build above, and full demolition with new build. Each has to be tested against the same brief, because an appraisal that measures retention against a reduced floor area and demolition against the optimised scheme has answered a different question.
Say what the brief is. Net internal area, floor to ceiling heights, servicing strategy and target rating all constrain what retention can deliver, and being explicit about them is more persuasive than a conclusion that retention is unfeasible.
What a structural appraisal actually has to test
A desk review of as built drawings is a starting point and nothing more. Records of existing buildings are frequently wrong, and the difference between the drawn slab and the built slab decides whether the scheme works.
A structural survey supporting a retention case should cover the grid and its compatibility with the proposed layout, existing floor loadings against the intended use, slab and beam capacity with any strengthening required, the condition of the concrete including cover, carbonation and reinforcement corrosion, lateral stability and the effect of new openings, foundation capacity for any added storeys, and whether the frame can accept the alterations without wholesale replacement.
Concrete testing is the part most often deferred and most often decisive. Core sampling for strength, cover meter surveys and half cell potential testing tell you whether the frame has the life the scheme needs. Deleterious materials matter too, since high alumina cement, woodwool shuttering and asbestos containing materials all change the cost and programme of a retention option.
For added storeys, the load path down to the foundations governs. A geotechnical review of the original design assumptions, and where necessary a geotechnical assessment, tells you whether the existing footings can take the additional load or whether underpinning and piling make retention uneconomic.
Comparing embodied carbon without cheating
A whole life carbon comparison is only useful if the two cases are drawn on the same basis. The RICS methodology sets the framework, and the assumptions that move the answer are the study period, the treatment of the existing structure, and whether benefits beyond the system boundary are reported separately.
Four assumptions deserve scrutiny in any comparison you submit or review.
- The study period. A 60 year reference period is conventional. A shorter period flatters new build by understating replacement cycles.
- The existing structure's carbon. It is already in the atmosphere, so a retention option should not be credited with it, and a demolition option should carry the end of life emissions of removing it.
- Module D. Benefits from future reuse and recovery sit outside the main total and should be reported separately rather than netted off.
- Operational carbon. A new building may perform better in use, and the comparison has to show the operational difference over the same period rather than asserting it.
A whole life carbon assessment prepared on that basis gives an officer a number they can rely on. One that reports a single figure with no stated assumptions invites the council's consultant to redo it, which is where applications lose months.
An illustrative example: a 1980s four storey office with a concrete frame on a tight urban site. Core testing showed adequate strength but low cover to the reinforcement on the south elevation. The retention option kept the frame and substructure, replaced the facade, and added one storey after the foundation review confirmed capacity. The carbon comparison used a 60 year period and reported module D separately. The floor to ceiling height on the second floor stayed below the applicant's target, and that was stated in the design and access statement rather than hidden.
Heritage and buildings that are valued locally
Where the building is listed, retention is the starting point and the question is the extent of intervention. Where it is a non designated heritage asset, including a locally listed building or an unlisted building that contributes positively to a conservation area, the Framework requires a balanced judgement having regard to the scale of any harm and the significance of the asset.
Two practical points. A building can be structurally poor and still significant, so the structural case does not answer the heritage case. And demolition in a conservation area needs planning permission in its own right, which means the replacement has to be acceptable before the loss can be considered.
If the building has any claim to local significance, commission the heritage work early. Discovering at committee that the local civic society has applied for local listing is a bad way to find out.
Viability arguments and how they are tested
Applicants often reach for viability when retention is technically possible and commercially unattractive. That argument can succeed, and it is tested hard.
The authority will instruct its own reviewer, usually working to the RICS approach to financial viability in planning, and will probe the existing use value, the benchmark land value, the assumed rents and yields and the abnormal costs attributed to retention. Abnormals are where retention cases are won and lost, so they need to be measured from the structural survey rather than estimated as a percentage.
Expect the reviewer to ask why a lower intensity retention scheme was not brought forward instead. Have an answer.
What to submit alongside the application
The pack for a demolition and rebuild in a policy sensitive area usually comprises the options appraisal, the structural appraisal, the whole life carbon comparison, a pre-redevelopment audit identifying materials for reuse and recycling, a circular economy statement where the authority requires one, heritage evidence where the building has significance, and a design and access statement that explains the option chosen and why.
Sequencing matters more than volume. The structural testing informs the carbon comparison, the carbon comparison informs the options appraisal, and the design and access statement reports the conclusion. Where the scheme involves mass timber in the replacement, the article on mass timber frames at planning stage covers the fire and insurance questions that follow.
This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
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Frequently asked questions
Is retrofit first national planning policy in England?
No. There is no national policy requiring retention to be tested before demolition. The expectation comes from the London Plan for referable schemes, from individual local plan climate and design policies, from heritage policy where the building has significance, and from design review panels. Once the carbon evidence is before an officer it becomes a material consideration regardless.
What should a structural appraisal cover for a retention case?
The grid and its fit with the proposed layout, existing floor loadings against the intended use, slab and beam capacity, concrete condition including cover, carbonation and reinforcement corrosion, lateral stability with new openings, and foundation capacity for any added storeys. Core testing and cover surveys are usually decisive, and as built drawings alone are not enough.
How long a study period should a carbon comparison use?
Sixty years is the conventional reference period, and using a shorter one flatters new build by understating replacement cycles. The comparison should also avoid crediting a retention option with the carbon already embodied in the existing structure, should charge demolition with end of life emissions, and should report module D benefits separately rather than netting them off.
Does demolition in a conservation area need permission?
Yes, demolition of a building in a conservation area requires planning permission in its own right. In practice that means the acceptability of the replacement has to be established before the loss can be considered. Where the building is a non designated heritage asset, the Framework requires a balanced judgement having regard to the scale of harm and the significance of the asset.
Can viability justify demolition where retention is feasible?
It can, and the argument gets tested closely. The authority will instruct its own reviewer, working to the RICS approach to financial viability in planning, and will probe existing use value, benchmark land value, rents, yields and the abnormal costs attributed to retention. Those abnormals need measuring from the structural survey rather than estimating as a percentage.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.