Whole life carbon at planning stage and the data problem

A whole life carbon assessment submitted with a planning application is a forecast made from a building that does not exist yet, using material quantities that will change and carbon factors that mostly come from industry averages rather than from the products that will be bought. That is not a criticism of the method. It is the condition under which the method has to work, and understanding it is the difference between an assessment that informs the design and one that produces a number nobody uses.

The professional standard in the United Kingdom is the Royal Institution of Chartered Surveyors' whole life carbon assessment for the built environment, second edition, published in 2023. It sets the scope, the modules to be reported and the rules for data quality, and it aligns with the European standard for assessing the sustainability of construction works.

Where the requirement comes from

There is no single national requirement in England for a whole life carbon assessment at planning stage. The requirement arises from local policy, and the most developed regime is in London, where the London Plan requires whole life-cycle carbon assessments for referable applications and the Greater London Authority publishes guidance and a reporting template.

Outside London the picture varies. A growing number of authorities require or encourage an assessment through local plan policy, a supplementary planning document or a validation checklist item, usually for major development. Some ask only for embodied carbon rather than the full life cycle. Check the adopted policy and the validation list for the authority rather than assuming a standard requirement exists.

Where no policy requires one, an assessment can still be worth doing, because it is the evidence that supports a design decision to retain an existing structure or to change a frame material.

Assessment stages and what planning stage covers

The standard divides the life cycle into modules. Product and construction stages cover extraction, manufacture, transport and the construction process. Use stage modules cover operational energy and water alongside maintenance, repair, replacement and refurbishment. End of life covers deconstruction, transport, waste processing and disposal. A separate module reports benefits and loads beyond the system boundary, such as reuse and recovery potential.

At planning stage the assessment is normally made at an early design stage, when the structural concept is set but the specification is not. What that supports is a whole-building estimate with a realistic breakdown by element, and a clear statement of the assumptions behind it.

What it cannot support is precision at product level. An assessment claiming three significant figures of accuracy from a stage two design is overstating what the input data can carry, and a reviewer who knows the method will say so.

Data quality and generic factors

Carbon factors come from environmental product declarations for specific products, from industry average declarations for a product type, or from generic datasets. Specific declarations are the most accurate and the least available at planning stage, because the products have not been selected.

The workable approach is to use industry average or generic data for the bulk of the model, to use specific declarations only where a product is already fixed, and to state the source and the data type for every element. Reviewers are far more comfortable with a transparent generic model than with a mixed model that does not say which is which.

Two data problems recur. Quantities at early design stage are derived from area and rate assumptions rather than from a measured schedule, so the quantity uncertainty is usually larger than the carbon factor uncertainty. And declarations vary in their boundaries and reference service life, so combining them without checking produces inconsistency that is hard to spot later.

Say what the uncertainty is. An assessment that reports a central figure alongside the elements driving most of the uncertainty is more useful, and more credible, than one that reports a single number.

Sensitivity to structural choices

The structure and substructure dominate embodied carbon in most buildings, which is where the assessment earns its fee if it is done early enough to influence anything.

The decisions that move the number most are whether an existing structure is retained, the frame material and grid, the substructure solution and its dependence on ground conditions, the façade build-up, and the extent of basement. Retention of an existing frame is usually the single largest saving available and is also the decision most constrained by the planning process, because it interacts with massing, floor-to-floor heights and unit numbers.

Run the comparison and report it. A planning submission that shows three structural options assessed on the same basis, with the chosen one explained, answers the policy question directly. One that reports a single figure for the chosen scheme invites the question of what was compared.

Be careful with end-of-life and beyond-boundary credits. Assumptions about future recycling rates and energy recovery are made about a demolition sixty years away, and authorities increasingly ask for the headline figure to be reported without those credits alongside the figure with them.

Reporting templates authorities expect

Where an authority has a template, use it. The Greater London Authority's reporting template is the most established, it is structured by module and by building element, and submissions that arrive in a different format get sent back.

Report, as a minimum, the assessment boundary and what was excluded, the design stage and the drawings the quantities came from, the modules assessed, the data sources by type, the gross internal area used for normalisation, the results by module and by element, and the comparison against any benchmark the policy names. Benchmarks published by industry bodies are used widely, and where you cite one, name the body, the publication and the version.

Normalisation matters more than people expect. A figure in kilograms of carbon dioxide equivalent per square metre is only comparable if the area definition is the same, so state which area measure you used.

Where the authority also expects a Circular Economy Statement, write the two together. They draw on the same material quantities, and inconsistencies between them are the most common review comment.

Updating at later stages

A planning-stage assessment is a starting point. Most policies that require one also require it to be updated as the design develops, and in London a post-construction assessment is expected.

Build that into the appointment. The quantity surveyor and the design team will need to hold the model in a form that can be updated rather than rebuilt, which means agreeing the element breakdown and the data conventions at the outset. An assessment produced as a one-off report by someone who then leaves the project is expensive to reproduce later.

Conditions sometimes require the updated assessment before a stated stage, so read what the decision notice actually asks for before assuming the planning stage report closes the matter.

Budgeting the work

The cost drivers are the design stage reached, the quality of the quantity information available, the number of options assessed and whether a template and benchmark comparison are required. Of those, the quantity information dominates: an assessor working from a measured schedule spends a fraction of the time of one deriving quantities from drawings.

The saving worth making is to commission the assessment at the stage where it can change the design rather than after the design is fixed. An assessment run at planning stage on a scheme that cannot now change its frame is a compliance cost. The same assessment run two months earlier is a design tool.

Councils expect a suitably qualified author for this work and professional review is strongly advised, because the method choices and the data conventions are contestable. A PlanScope draft of the supporting narrative is a starting point for that professional rather than a substitute for the assessment itself. A Whole Life Carbon Assessment and the accompanying Sustainability Statement should be written to the same assumptions.

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.

See PlanScope pricing if you are costing the supporting documents alongside the assessment work.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.