Whole life carbon modules C and D at end of life

Modules C and D sit at the end of a whole life carbon assessment and they are the two most often misused. Module C is the carbon of taking the building apart and dealing with the material: demolition, transport, processing and disposal. Module D is everything beyond the system boundary, meaning the benefits and loads that arise elsewhere because your materials get reused, recycled or burned for energy. Module D must be reported separately and must never be netted off the rest.

Where a scheme claims a low whole life figure, module D is usually where the claim is hiding.

What modules C and D each represent in the assessment

Module C divides into four stages under BS EN 15978, applied in the United Kingdom through the RICS whole life carbon assessment methodology:

• C1, deconstruction and demolition, covering plant fuel and site energy
• C2, transport of waste from site to the receiving facility
• C3, waste processing for reuse, recovery or recycling, meaning sorting, crushing, shredding and preparation
• C4, disposal, meaning landfill or incineration without energy recovery

Module D stands outside the system boundary. It records the avoided emissions elsewhere in the economy attributable to material leaving your building in a usable state, plus any energy exported from the site over the study period.

Module C is normally modest against upfront embodied carbon, often in the low single digits as a percentage of the total for a new build. That is not a reason to skip it. It is where the assumptions about what happens to your materials get written down, and those assumptions are what module D then trades on.

Demolition, transport and waste processing carbon

C1 is calculated from plant fuel use, and on most assessments it comes from a rate per tonne or per square metre of demolished structure rather than from a plant schedule. State which.

C2 depends on distance and vehicle type, and it is the stage where default assumptions do most of the work. Where the receiving facility is unknown, assessments apply a default haulage distance, and that default should be stated rather than buried. On a scheme where the concrete will be crushed on site and reused, the distance is effectively zero and the assessment should say so with the site waste strategy as the evidence.

C3 covers the energy of processing. Crushing concrete to a graded aggregate has a carbon cost, and so does sorting mixed waste at a materials recovery facility. Where a scheme claims high recycling rates, the processing carbon that makes those rates possible belongs in C3 rather than being quietly omitted.

The evidence base for all three sits in the demolition and waste documentation. A Pre-redevelopment Audit establishing what is in the existing building, by material and quantity, is what turns C1 to C4 from a per-square-metre estimate into a calculation, and a Site Waste Management Plan records what will actually happen to each stream.

Disposal assumptions and landfill treatment

C4 is where end-of-life scenarios show their teeth.

The methodology expects current end-of-life practice rather than aspirational future rates, unless a departure is justified. An assessment assuming 95 per cent recovery of a composite cladding panel, on the basis that recycling technology will have improved by 2085, is making a claim about the future rather than assessing the building. Use present-day rates, state them, and if you want to show an optimistic scenario, show it as a sensitivity.

Biogenic carbon is the substantive issue and it is regularly got wrong. Where sequestered carbon in timber has been reported as a negative figure in the product stage, that carbon has to be reversed at end of life in C3 or C4 unless the material is demonstrably retained in long-term use. A timber-framed building that books the sequestration benefit upfront and then assumes the timber vanishes at end of life has counted a benefit that never existed. Landfilled timber also generates methane, which carries a higher warming effect than the carbon dioxide originally absorbed.

So the honest treatment is symmetrical. Report the sequestration, report the reversal, and state the assumed end-of-life route for each biogenic material. Where the timber is assumed to be reused, that assumption belongs in module D with the reasoning attached.

Why module D is reported separately

Because it is not the building's carbon. It is a projection about someone else's process, decades from now, and the methodology treats it as information rather than as performance.

Three practical consequences:

1. Local authority benchmarks are set on upfront carbon, meaning modules A1 to A5, so a module D benefit does nothing for compliance with a policy target expressed that way.
2. A single net figure combining A, B, C and D is not a reportable output, and presenting one invites the reviewer to recalculate.
3. Comparing two schemes on net-of-D figures compares two sets of assumptions rather than two buildings.

Where a design team wants credit for designing for disassembly, module D is the right place to show it, alongside the design measures in a Circular Economy Statement that explain how the material will actually be recovered. Bolted connections, mechanically fixed cladding, avoidance of composites and material passports are what make a module D claim credible.

Reuse, recycling and recovery potential

Module D distinguishes between three routes and they carry very different values.

Reuse of a component in its existing form, such as steel sections carefully deconstructed and re-certified, avoids the entire production process and is the largest benefit available. It is also the hardest to substantiate, because it depends on connection design, on testing at the point of reuse, and on a market existing at the time.

Recycling, meaning reprocessing the material into new feedstock, avoids primary production but incurs the processing burden. For steel and aluminium the avoided burden is substantial. For concrete, crushed material usually displaces primary aggregate rather than cement, so the benefit is much smaller than the tonnage suggests.

Recovery, meaning energy from waste, gives a benefit only where the displaced energy is carbon-intensive. As the grid decarbonises, the avoided emissions from burning material for electricity shrink towards nothing, and an assessment using today's grid factor for a combustion event in 2080 overstates the benefit heavily.

Avoiding double counting with reuse claims

This is the error a reviewer looks for first.

Steel is the standard case. If the product stage figure for your steel already reflects recycled content, using an environmental product declaration based on a high scrap input, then claiming a further module D benefit for the same steel being recycled at end of life counts the same avoided production twice. The methodology handles this through the allocation approach, and the assessment has to be explicit about which approach it uses.

The same trap appears with retention. Keeping an existing structure produces a benefit in the product and construction stages, because you buy less new material. It does not also produce a module D benefit for the material you did not demolish. Where an assessment shows both, the baseline problem in a refurbishment assessment is usually the underlying cause.

Check three things in any assessment claiming large module D values. Does the product stage data already account for recycled content? Is the end-of-life recovery rate drawn from current practice? And does the grid factor used for energy recovery follow a decarbonisation trajectory?

Presenting end of life results honestly

Report by module, in a table, with A1 to A5, B, C1 to C4 and D as separate lines and no net total. Give the study period. State the end-of-life scenario for each main material with its source. State the biogenic carbon treatment and where the reversal appears. State the allocation approach for recycled content. State the grid trajectory used for any energy recovery benefit.

Then say what the numbers mean. A scheme with high upfront carbon and a large module D benefit is a scheme betting on the future, and a planning authority is entitled to know that is the position. Saying so plainly is better received than a net figure that collapses under a single question.

Councils usually expect a suitably qualified author for a Whole Life Carbon Assessment, and professional review is strongly advised before the figures support a planning condition. Where the assessment sits alongside a Sustainability Statement, keep the material claims consistent across both.

This is general guidance rather than 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.