Arguing against demolition on carbon grounds

Arguing retrofit first means arguing that the carbon already locked into an existing building is a material consideration weighing against demolition, and that the applicant has not properly tested retention. The argument only works when it is quantified. A committee can be persuaded by a whole life carbon comparison between a refurbishment option and a demolish-and-rebuild option, run over the same study period on the same functional unit. It will not be persuaded by an assertion that reuse is better in principle.

That is the opening position for anyone promoting retention, and also for anyone defending a demolition scheme. The side with the modelled comparison usually prevails, and the side without one looks unprepared.

Why demolition became a planning question

For most of the past three decades, demolition of an unlisted building outside a conservation area attracted very little planning scrutiny. Operational energy was regulated through the Building Regulations and embodied carbon was not regulated at all.

That has changed through policy rather than through legislation. The Framework supports making effective use of land and existing resources. In London, the London Plan 2021 requires whole life-cycle carbon assessments and circular economy statements for referable applications, and the Mayor's guidance expects applicants to demonstrate that retention and refurbishment options have been explored before demolition is accepted. A growing number of authorities outside London have adopted similar local policy or supplementary guidance, with varying rigour.

The practical consequence is that embodied carbon is now a material consideration in many authorities. How much weight it carries is a matter for the decision maker, and that is where the argument happens.

Comparing options on whole life terms

A credible comparison follows the whole life carbon method set out in the RICS professional standard, second edition, which reports emissions by life cycle module.

The modules do different work in this argument. A1 to A3 cover product manufacture and are where a new structural frame concentrates its emissions. A4 and A5 cover transport and construction, including demolition and waste. B1 to B5 cover maintenance, repair and replacement over the study period. B6 and B7 cover operational energy and water, which is where a deep retrofit of a poorly insulated building can lose ground to a new build. C1 to C4 cover end of life, and module D covers benefits beyond the system boundary such as reuse and recovery, reported separately.

Two methodological points decide whether a comparison survives scrutiny. The study period has to be the same for both options, and 60 years is the conventional figure. The functional unit has to be comparable, which is the hard part: if the retrofit option delivers 20 per cent less floorspace, the comparison per square metre is not the comparison the applicant is actually proposing, and that difference has to be stated openly rather than buried.

Operational carbon assumptions deserve the same scrutiny. A new building modelled against a decarbonising grid over 60 years shows much lower operational emissions than one modelled against today's carbon factors, and the choice of factor can reverse the conclusion. Ask which grid decarbonisation trajectory has been used and whether both options use the same one.

What an option appraisal must contain

An appraisal that an authority can rely on has six components, and a scheme missing any of them invites a request for further information.

1. A condition survey of the existing building, with the structural capacity, the services condition and the presence of deleterious materials recorded.
2. A statement of the functional brief, so the reader knows what each option has to deliver.
3. At least three tested options: light refurbishment, deep retrofit including fabric and services, and demolition with rebuild, plus any partial retention option the structure allows.
4. A whole life carbon assessment of each option on the same basis, with the modules reported separately.
5. An operational energy assessment of each option against the same assumptions.
6. A reasoned conclusion that explains why the preferred option was chosen, including where carbon was traded against something else.

The sixth is the one most often skipped, and it is the one a committee reads. An appraisal that concludes demolition is preferable on carbon grounds alone is rare. An appraisal that concludes demolition is preferable because retention cannot deliver the floorspace, the floor-to-ceiling heights or the accessibility standards required, and that quantifies the carbon cost of that choice, is defensible.

The documents themselves are a Whole Life Carbon Assessment and, where the policy requires it, a Circular Economy Statement setting out material reuse, recycling rates and the pre-redevelopment audit of what is already on site.

Structural capacity as the limiting factor

Most retention arguments stand or fall on the frame, and the answer is usually knowable before any carbon modelling is done.

The questions are specific. What imposed load was the floor designed for, and what does the new use require? What is the floor-to-floor height, and does it allow the services zone a modern fit-out needs? Is the grid usable for the proposed layout? What is the condition of the concrete, and does testing show carbonation or chloride attack that limits remaining life? Is there a lateral stability system that can take any added storeys? Are there deleterious materials, high alumina cement, asbestos or woodwool shuttering, that make intervention expensive?

A 1960s office frame designed for a light imposed load will not take residential loading without strengthening, and the carbon cost of that strengthening belongs in the retrofit option rather than being left out of it. Equally, a 1980s frame with generous floor-to-floor heights and a usable grid is often a better starting point than the design team's first instinct suggests. A proper Structural Survey early on settles the argument for less money than a sequence of carbon models based on assumptions.

An illustrative example

This example is illustrative. A 1970s concrete-framed office of 8,000 m2 is proposed for demolition and replacement with 11,000 m2 of mixed use. The applicant's whole life carbon assessment shows the new build at a lower figure per square metre over 60 years, driven by operational savings. An objector's reviewer points out that the retrofit option was modelled with the existing single glazing retained and no heat pump, which is not a deep retrofit at all. Re-modelling the retrofit option with a full fabric upgrade and air source heat pumps brings it below the new build on total emissions, though it delivers 2,400 m2 less floorspace. The argument then becomes a planning balance about floorspace against carbon, which is a better argument for everyone than a dispute about the model.

How objectors use the carbon case, and what persuades a committee

Objectors use the carbon case in two ways. The first is to attack the adequacy of the appraisal, which is usually the stronger route, because an appraisal with an unrealistic retention option is easy to discredit. The second is to argue weight, which depends entirely on the local policy position.

What persuades a committee, in rough order of effect:

• A side-by-side table of total emissions per option, with the modules shown, on one page.
• Evidence that the retention option was tested with a design team, not estimated.
• An independent review of the assessment, where the authority has commissioned one.
• A clear statement of what retention cannot deliver and why that matters in planning terms.
• Material reuse commitments secured by condition, with a pre-redevelopment audit behind them.

What does not persuade: a claim that the new building is net zero in operation, which answers a different question; a comparison against a notional baseline building rather than against the actual existing one; and a circular economy statement that recites policy without quantities.

Where heritage sits alongside carbon, the arguments reinforce each other. A non-designated heritage asset attracts a balanced judgement about the scale of harm, and the carbon case gives that judgement additional substance. The detailing side of a deep retrofit, particularly where insulation meets an existing structure, is where retrofit schemes most often come unstuck, and our note on thermal bridging detail at planning stage covers what to resolve early.

Model the retention option properly, even if you intend to demolish. Enter your postcode on PlanScope to see which energy and carbon reports your scheme is likely to need.

This is general guidance, not legal advice. Check the policy position with the 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.