Whole life carbon: modules A to C and what gets reported

Whole life carbon modules A to C are the reporting structure, not a methodology, and getting the structure right is most of what a planning officer checks. The modules come from BS EN 15978 and the product-level rules in the associated European standard, and they divide a building's emissions into product and construction (A), use (B), end of life (C), and benefits beyond the system boundary (D).

Whole life carbon is A plus B plus C. Module D is reported separately and does not count towards the total. Treating module D as an offset against module A is the error that gets assessments sent back.

What the modules cover

The A modules cover everything up to practical completion. A1 to A3 are raw material supply, transport to the factory and manufacturing, together often called cradle to gate. A4 is transport from factory to site. A5 is the construction process itself, which the RICS methodology subdivides into site preparation and demolition, construction waste, and construction activities including plant, temporary works and site energy.

The B modules cover the building in use. B1 is emissions from the materials in service, which in practice means refrigerant leakage and the carbonation of concrete. B2 is maintenance, B3 repair, B4 replacement and B5 refurbishment. B6 is operational energy and B7 operational water.

The C modules cover the end of the reference study period. C1 is deconstruction and demolition, C2 transport of waste, C3 waste processing for reuse or recycling, and C4 final disposal.

Module D sits outside the boundary and records the benefits and loads of reuse, recovery and recycling, plus any exported energy.

Two derived terms get used loosely and should not be. Upfront carbon is A1 to A5. Embodied carbon is everything except B6 and B7. Whole life carbon is the lot, excluding D.

Product and construction stage emissions

A1 to A3 usually dominate, and the quality of the assessment depends almost entirely on the data used for them.

The data hierarchy runs from product-specific, third-party verified Environmental Product Declarations, through sector-average declarations for a material group, to generic database figures. An assessment built entirely on generic data is acceptable at concept stage and loses credibility at planning stage for a large scheme, because the design should by then be specific enough to name products for the major elements.

A4 is small and frequently miscalculated by assuming a default distance for everything, including imported stone and steel. A5 is the module most often understated. Site preparation, demolition of existing structures, the carbon in construction waste including the wastage allowance on each material, and the diesel and electricity used on site all belong there, and leaving out demolition on a site with an existing building removes a large number from the answer.

State the assumptions for A5 explicitly. An assessor who reports A5 as 3 per cent of A1 to A3 without saying so has not assessed it.

Use stage, and why B4 dominates it

B4 replacement is usually the largest of the B modules apart from operational energy, and the reason is arithmetic. The reference study period for buildings under the RICS methodology defaults to 60 years. A component with an assumed service life of 30 years is replaced once. A floor finish with a 10-year life is replaced five times, each replacement carrying its own A1 to A5 and C1 to C4.

So the assumed service lives drive the result, and they are an assumption rather than a measurement. Two assessments of the same building can differ by a third on B4 alone. Where a design choice is intended to reduce replacement cycles, say which component and what life you have assumed, and cite the source for the assumption.

B1 deserves more attention than it gets. Refrigerant leakage over 60 years, with a high global warming potential refrigerant in a large system, can be a material number, and the choice of refrigerant is a design decision with a carbon consequence, as the note on refrigerant choice and global warming potential sets out.

B6 operational energy is reported separately from the embodied modules and uses the energy model rather than the materials model. Because it is projected over the study period, it shrinks as grid decarbonisation assumptions are applied, which is why the embodied share of a new building's whole life total has grown relative to the operational share. That shift is the policy reason whole life assessment is now required at all, and it is why the Energy Statement and the carbon assessment have to use the same energy model.

End of life and beyond the boundary

C1 to C4 are typically a small proportion of the total, and they are still worth doing properly because the assumptions about them feed module D.

The temptation is to assume high recycling rates in 60 years' time and to report a large module D credit. Report it, by all means. Do not net it off. The GLA guidance and the RICS methodology both treat module D as separate information, and a total that includes a D credit is not a whole life carbon figure.

Where a scheme retains an existing structure, the comparison that persuades is a like-for-like assessment of the retention option against the demolition and new build option, with both carried through A to C on the same assumptions and the same study period. That comparison, rather than a module D credit, is what makes a reuse case.

What a planning submission has to report

For applications referable to the Mayor of London, policy SI 2 of the London Plan requires a whole life-cycle carbon assessment, submitted on the GLA template, at application stage and again after construction. The guidance sets out which modules to report and publishes benchmarks and aspirational figures by building type in kilograms of carbon dioxide equivalent per square metre of gross internal area. Take those figures from the current guidance rather than from an earlier scheme's report, because they are revised.

Outside London the requirement comes from the local plan. Some authorities require the full A to C set. Many require upfront carbon, A1 to A5, with a target figure. Some require nothing. Read the adopted policy and any supplementary document before scoping the work.

Where the policy requires a Whole Life Carbon Assessment, councils usually expect it to be prepared by an assessor with relevant experience, and professional review is strongly advised before submission. An AI-assisted draft can structure the report, set out the module definitions and assemble the policy context, and the calculation itself needs the assessor and the model.

Presenting results a reviewer can follow

Six things make an assessment checkable, and their absence makes it unreviewable.

1. A module-by-module table reporting absolute emissions and emissions per square metre of gross internal area, with the floor area definition stated and the area figure given.
2. The reference study period and the reason if it is not 60 years.
3. A breakdown by building element using recognised element categories, so substructure, superstructure, facade, services and finishes can be compared against benchmarks.
4. A data quality statement saying what proportion of the A1 to A3 result came from verified product declarations and what came from generic data.
5. The carbon factors and grid projection used for B6, cross-referenced to the energy assessment.
6. Module D reported separately, clearly outside the total.

Add a short section on the design decisions the assessment drove. A whole life carbon assessment produced after the design is frozen is a compliance document. One produced during concept design, with an iteration recorded, is evidence that the policy worked, and reviewers notice the difference.

And where the scheme includes material reuse or a retention strategy, keep the carbon assessment and the Circular Economy Statement consistent. The two documents routinely report different recycled content and different diversion rates for the same building.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. For specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. To see which sustainability documents your scheme needs, enter your postcode on PlanScope.