Carbon in demolition and site enabling works

Demolition and site clearance sit in module A5 of a whole life carbon assessment, and in the RICS methodology the pre-construction demolition work is reported separately from construction activities on site. That split matters, because demolition phase carbon module a5 figures are where a retain-or-demolish argument is either won or quietly avoided. Most assessments submitted with planning applications treat A5 as a rounded percentage of the product stage and move on. A committee that has read the circular economy policies will ask for better than that.

The honest position is that the data is harder to get than product stage data, and the answer is usually smaller than objectors expect and larger than the design team assumed.

Where demolition sits in the module structure

BS EN 15978 gives the module framework and the RICS Whole Life Carbon Assessment for the Built Environment, 2nd edition, sets out how UK practice applies it. Pre-construction demolition and site preparation are reported within A5, split out from construction activities and from construction waste. The C modules cover the end of life of the building you are proposing, not the end of life of the building you are knocking down.

That distinction trips up a lot of submissions. If you put existing building demolition into C1, the assessment double counts nothing but it does hide the number the planning debate is about. Report it in A5 and label the sub-module.

Enabling works are the other gap. Piling mats, temporary haul roads, site hoardings, dewatering, ground remediation and the diversion of services all have embodied and operational carbon, and they routinely fall outside the assessment boundary because nobody owns them at the point the assessment is written. Set the boundary in writing at the start and state what is excluded.

The data that carries the result

Three inputs carry almost all of the result: the mass of material arising, the distance it travels, and how it is treated at the destination. Everything else is secondary.

1. A pre-demolition audit giving material quantities by type, from a survey rather than an assumption.
2. Plant schedules with fuel type and estimated running hours for breakers, crushers, excavators and dewatering pumps.
3. Vehicle movements: number of loads, payload, round trip distance and whether the return leg runs empty.
4. Destination and treatment route for each material stream, with recovery, recycling and landfill separated.
5. Site electricity and any temporary generation, with the supply arrangement stated.

PlanScope's Whole Life Carbon Assessment report drafts the structure and the policy narrative around those inputs and inserts a to-be-confirmed flag wherever a quantity is missing, which is a useful discipline: it makes the holes visible before the officer finds them. Councils expect a suitably qualified author for this report type, and professional review is strongly advised.

Transport and disposal usually dominate

Concrete and masonry are heavy and low value, so haulage does the damage. A demolition arising crushed on site for reuse as sub-base carries the plant fuel of crushing. The same material taken off site to a recycling facility and replaced with imported aggregate carries two haulage legs plus the crushing, and the round trip distance is often 30 to 50 kilometres in urban areas where local facilities have closed.

On-site crushing is therefore the first measure to test, before anything clever. It reduces both export and import tonnage at the same time. The constraints are noise, dust and space, which is why the crushing proposal has to be consistent with whatever you are telling the environmental health officer about the construction phase.

Waste classification drives the treatment route and the cost. Material that is hazardous, or that cannot be shown to meet end-of-waste criteria, cannot be reused on site whatever the carbon case says. Get the classification right early, because a late reclassification of made ground changes the tonnage going to landfill and with it the A5 figure.

Retention against demolition as a carbon test

The comparison is not symmetrical, and pretending it is will get the assessment picked apart. Retention avoids the demolition arisings and most of the new substructure and frame, and it carries its own burdens: strengthening, new openings, remedial work to the existing fabric, and often a worse operational performance over sixty years.

A defensible comparison needs a stated study period, the same functional unit on both sides, and both embodied and operational carbon shown separately so the crossover point is visible. State the assumed grid decarbonisation trajectory, because the year at which the retained building stops being the better option depends almost entirely on that assumption.

Illustrative example: a 1970s three storey office of 2,800 m2 on a suburban edge-of-centre site, where the frame is sound but the floor-to-ceiling heights are tight. The retention option keeps frame and substructure and adds a new envelope. The rebuild option gains about 15 per cent more lettable area. The carbon answer turns on the study period and the grid assumption, and the planning answer turns on whether the extra area is needed. Figures in this example are illustrative only.

Reduction measures available in practice

Most of the levers are procurement and logistics rather than design.

Crush and reuse on site where the classification allows it. Specify recycled content in the new substructure so the arisings have somewhere to go. Consolidate deliveries and set a minimum payload in the contract. Choose a demolition contractor who will report actual tonnages and haulage distances rather than modelled ones, and write the reporting obligation into the appointment. Retain the substructure and basement slab where the new layout can work with it, because that is the single largest avoidable quantity on most urban sites.

Soft strip reclamation is worth doing for material value and for the circular economy narrative, and it will not move the headline carbon figure much. Be straight about that rather than overclaiming.

Presenting the comparison to a committee

Members do not want module tables. They want to know whether the scheme took retention seriously, and what the alternative would have cost in carbon and in floor area.

Lead with one chart and three numbers: upfront carbon for each option, the crossover year, and the proportion of demolition arisings diverted from landfill. Put the module breakdown in an appendix. Say what is uncertain, because an assessment that claims precision it cannot have invites the objector's consultant to attack the method instead of the conclusion.

Tie it to the rest of the submission. A Sustainability Statement that promises high recycled content while the demolition strategy exports everything to landfill is the sort of inconsistency that gets picked up at consultation. The same applies to phasing: if enabling works start before the main contractor is appointed, the assessment boundary needs to say who reports them. Similar coordination issues come up on large single-building schemes, as our note on energy statements for warehouse and logistics schemes sets out.

And set the reporting condition yourself. Offering a post-construction carbon report as a condition is better than having one imposed with wording you cannot meet.

Enter your postcode on PlanScope to see which reports a demolition and redevelopment scheme at your site is likely to need. 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.