Whole life carbon assessment: which modules a council expects

A whole life carbon assessment is structured by lifecycle module, and the first question a council asks is which modules you reported. The RICS professional standard on whole life carbon assessment for the built environment sets the module structure, and it is the reporting framework that planning authorities have adopted where they require the assessment at all. Get the module coverage wrong and the number you present cannot be compared with anything.

The short answer for most English authorities that require one: report the product and construction stages, the use stage, the end of life stage and the benefits beyond the system boundary, each separately, with a single total that states what it includes.

What the lifecycle modules cover

The modules follow the European standard structure for sustainability assessment of construction works, which the RICS standard applies to buildings and infrastructure in a UK context.

Module D sits outside the building's own total by design. It records the benefit available to the next system from materials recovered at end of life, and it is reported separately rather than netted off, because doing otherwise lets a scheme claim a reduction for something that has not happened yet.

Operational energy under B6 overlaps with what the energy statement reports, and the two documents should use the same model and the same assumptions. Where they do not, the assessor has usually run one against a different baseline than the other.

Product and construction stage reporting

Modules A1 to A5 are where design decisions show up most clearly, and they are the modules with the best data.

Report the quantities by material from the cost plan or the model, with the unit carbon factor used for each and its source. Environmental product declarations specific to the proposed product are the strongest evidence. Generic database factors are acceptable at planning stage provided you say which database and which version, and provided you do not mix a manufacturer declaration for one material with a generic figure for another without saying so.

Module A5 deserves more attention than it usually gets. It covers site activities, and in the second edition of the RICS standard that includes pre-construction demolition and site clearance. On a brownfield site with a building to remove, A5 can carry a substantial share of the total, and it is the module that makes the retention case visible. If demolition emissions are reported inside A5, say so, because comparing a total that includes them against one that does not is meaningless.

Substructure is the other place the number moves. Piled foundations on poor ground can outweigh a great deal of careful specification in the superstructure, which is one reason the assessment belongs alongside the ground investigation rather than after it.

Use stage replacement cycles

Modules B2 to B5 depend almost entirely on the service life you assume for each component, and assumed service life is the least examined input in most assessments.

State the assumed service life for each major element and its source. A facade assumed to last sixty years and a facade assumed to last thirty produce very different totals over the same assessment period, and the difference is invisible unless the assumption is written down. The reference study period is normally sixty years for buildings, and any departure from that needs stating.

Two honest difficulties. Service life data for newer systems is thin, so the assumption is often an estimate rather than a measured figure. And a component with a shorter service life may still be the better choice on a whole life basis if it is lighter, simpler to replace or recyclable. Report both the figure and the reasoning.

Where the scheme uses offsite manufacture, the replacement and disassembly assumptions change, and the wider argument is set out in modern methods of construction and the carbon case.

End of life and beyond the system boundary

Modules C1 to C4 are modelled rather than measured, and everyone knows it. The value of reporting them lies in the comparison between design options rather than in the absolute figure.

State the end of life scenario assumed for each material: reuse, recycling, energy recovery or landfill, with the proportion assumed for each. Where the assumption is optimistic, say so. An assessment that assumes ninety per cent recycling of a composite panel system that cannot currently be separated is not credible, and an officer who has read a few of these will notice.

Module D then reports the potential benefit from those recovered materials. Keep it visibly separate from the total.

Infrastructure is frequently left out entirely. Roads, drainage, retaining structures and utility diversions carry real embodied carbon, and on a large site they can rival the buildings, as carbon in the infrastructure a scheme has to build sets out. State whether they are in or out of your assessment boundary.

Benchmarks and how to use them honestly

Published benchmarks exist for embodied carbon in buildings by type, expressed in kilogrammes of carbon dioxide equivalent per square metre of gross internal area, and industry bodies publish target and limiting values.

Three rules for using them. Compare like with like on module coverage, because a benchmark covering A1 to A5 cannot be compared against a total that includes B and C. State the floor area definition you used. And do not present a benchmark as a policy requirement unless the local plan actually adopts one, because most do not.

Where a local plan or supplementary guidance does set a figure, cite it directly and report against it. Where it does not, report against the published industry benchmarks and say that is what you are doing.

Assumptions that need stating

The assessment is only as useful as its assumption schedule. Put it at the front rather than in an appendix.

• The reference study period and why.
• The modules included, and any excluded with the reason.
• The carbon factor database and version, and any product-specific declarations used.
• The floor area definition and the measured area.
• Assumed service lives for major elements.
• End of life scenarios by material.
• The treatment of demolition and site clearance.
• Whether external works, infrastructure and fit-out are inside the boundary.
• The design stage at which the quantities were taken, since a stage two estimate carries different confidence from a stage four one.

Officers who read many of these can tell within a page whether the assessor has been careful, and the assumption schedule is what tells them.

Where the assessment changes a design decision

The point of running it at planning stage is that it can still change something.

Retention against demolition is the decision with the largest carbon consequence available on most sites, and it is the one the assessment exists to inform. Structural frame selection is second. Foundation solution is third, and it is often the one nobody looks at. Facade specification and service life come fourth, and the choice between a long-life simple facade and a shorter-life complex one is a real argument.

Run the assessment early enough to matter. A whole life carbon assessment produced two weeks before submission documents a decision that has already been made. One produced at concept stage changes it.

Draft it alongside the energy statement so that the operational and embodied positions are consistent, and alongside the circular economy statement where the borough requires one, since the material recovery assumptions have to match across both.

For specialist technical reports, qualified professional input may be required. This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.