Cumulative effects chapters: which schemes to include
The EIA Regulations 2017 require cumulation with other existing and approved projects, but set no radius or cut-off date. Here is how to build, agree and defend the scheme list.
A cumulative effects assessment includes the schemes that a reasonable assessor would expect to interact with yours, and the list is a judgement you have to defend rather than a search result you can print off. The Town and Country Planning (Environmental Impact Assessment) Regulations 2017 require the Environmental Statement to describe the likely significant effects arising from the cumulation of effects with other existing and approved projects. They do not tell you the radius, the cut-off date or the status threshold. Those you agree with the local planning authority, in writing, before the assessment work starts.
Get that wrong and the consequence is practical. A cumulative chapter built on the wrong list invites a request for further information under regulation 25, which stops the clock on a determination period that was already 16 weeks.
What cumulation means in the Regulations
Two ideas travel under the same word and it pays to separate them in the chapter's opening paragraph.
Inter-project cumulation is the effect of your scheme added to the effects of other development: two housing sites feeding the same junction, three wind turbine clusters in one view. Intra-project or in-combination cumulation is the effect of several of your own residual impacts landing on the same receptor at the same time, such as construction noise, dust and loss of outlook on one row of houses.
Schedule 4 of the 2017 Regulations covers the first. Schedule 3, which sets the screening selection criteria, also lists cumulation with other existing and approved development among the characteristics of development that a screening opinion must weigh. So the question arrives before you have a single technical chapter, at the point where you ask whether an Environmental Impact Assessment is needed at all.
Define both terms in the chapter. Inspectors and officers read a lot of these and they should not have to work out which meaning you are using.
Building the committed development list
The list is assembled from public registers and then filtered. Start with the local planning authority's own application search and pull everything validated, resolved, permitted or under construction within your outer radius. Then add the sources people forget.
- Site allocations in the adopted local plan and in any plan at examination
- Resolutions to grant subject to completion of a section 106 agreement, which are not yet decisions
- Appeals allowed by the Planning Inspectorate in the past two years that have not started
- County-level minerals and waste permissions, held by a different authority from the district
- Development consent orders for major infrastructure projects
- Applications in adjoining authorities, which your site search will miss entirely
Record each scheme with a reference number, a short description, the quantum, the decision status, the distance and bearing from your site, and the date you checked. That table becomes an appendix and it is the thing a consultee will interrogate.
Status matters more than proximity. A scheme under construction belongs in the baseline, not in the cumulative assessment, because its traffic and its habitat loss have already happened. A permission with three years left to run and no material start is a live cumulative scheme. An allocation with no application is usually too uncertain for quantitative work but may still warrant a paragraph of qualitative comment.
Search radius and the cut-off date
There is no single radius, and a chapter that applies one distance to every topic is doing it wrong.
| Topic | What sets the radius |
|---|---|
| Transport | The extent of the modelled network and the junctions where flows overlap |
| Air quality | Distance to relevant receptors and the dispersion modelling domain |
| Noise and vibration | Construction plant screening distances and shared receptor groups |
| Landscape and visual | The zone of theoretical visibility and the agreed viewpoint set |
| Ecology | Functional connectivity of habitat for the species recorded on site |
| Socio-economic | The catchment for schools, health provision and labour supply |
The cut-off date is a single freeze point for the register search, stated in the chapter and repeated in the appendix. Pick a date close enough to submission that the work is current, and far enough back that the technical modelling can actually be completed against it. Six to eight weeks before submission is workable on most schemes. Say what it is and say what you did about anything permitted after it.
In-combination effects across topics
This is where cumulative chapters usually go thin. The mechanism is simple: take the residual effects table from every technical chapter, identify the receptors that appear in more than one, and then form a view about the combined experience at that receptor.
A terrace of six houses 40 metres from a site access may face a moderate adverse construction noise effect, a minor adverse dust effect and a moderate adverse visual effect over an 18-month programme. None of those alone triggers a refusal recommendation. Together they describe a household that has a hard year and a half, and the honest assessment says so, then points at the mitigation that shortens or shifts the overlap.
Do not add significance categories arithmetically. Two minor adverse effects are not one moderate adverse effect. Describe the overlap, explain the duration, and reach a reasoned conclusion.
Agreeing the list with the authority
Use the scoping request. Regulation 15 lets you ask the authority for a scoping opinion, and the authority must consult the bodies it would consult on the application itself. Put the draft scheme list in the scoping report as a table, with a column showing which topics each scheme is scoped into and which it is screened out of, and a sentence of reasoning for each exclusion.
Ask three specific questions rather than inviting general comment: is the list complete, are the radii acceptable per topic, and is the cut-off date agreed. Copy the highway authority, the Environment Agency and Natural England where their topics are engaged, because they are the consultees who will later say a scheme was missed.
Where the authority adds a scheme you think is irrelevant, assess it and say why the effect is negligible. That costs a paragraph. Arguing about it costs a month.
Updating the list during determination
Between validation and decision, other applications get permitted. The chapter needs a stated rule for what happens next, agreed at scoping: a change note for schemes that do not alter any significance conclusion, and a formal addendum where a conclusion moves.
Set a materiality threshold for re-running quantitative work. For transport, that is usually a percentage change in flow on a link or arm that the modelling is sensitive to, agreed with the highway authority when the Transport Assessment methodology is signed off. For landscape, it is whether a new scheme appears in an agreed viewpoint. Without a threshold, every new permission in the district becomes a reason to reopen the assessment.
Presenting the assessment without duplication
Two structures work. Either each technical chapter carries its own cumulative section and a short collating chapter summarises them, or a single cumulative chapter does all the assessment while the technical chapters cross-refer to it. The first is easier for specialists to write and easier for consultees to check, and it keeps methodology with the topic. The second reads better but tends to lose the modelling detail.
Whichever you choose, the scheme table lives in one place only, the significance criteria are the ones used in the parent chapters, and the visual material follows the agreed methodology, including the same photomontage methodology used for the single-scheme views. Repeating the same assessment in two places is how contradictions get into an Environmental Statement.
Illustrative example: a 180-dwelling scheme on the edge of a market town shares a signalised junction with a permitted 400-dwelling allocation 1.2 kilometres away that has not started, and sits within the visual envelope of a consented poultry unit. The transport chapter models the 400 homes as committed development at full build-out. The landscape chapter includes the poultry unit in two of seven agreed viewpoints. The ecology chapter screens both out, because neither affects the hedgerow network the bat activity survey identified. Figures here are illustrative and are not drawn from a real application.
PlanScope can draft the structure and policy framing of an Environmental Impact Assessment, and its drafts flag missing site facts rather than filling them in. An Environmental Statement must be prepared by competent experts under the 2017 Regulations, so treat any draft as the starting point for those experts rather than a substitute for them. For a first view of which reports a site is likely to need, enter your postcode on PlanScope.
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.
Frequently asked questions
Does the cumulative assessment include schemes already built?
No. Development that is complete and operating belongs in the environmental baseline, because its traffic, emissions and habitat loss are already captured by the surveys. Cumulative assessment covers approved but unimplemented schemes, resolutions to grant, and in some cases allocations. Say explicitly in the chapter where you have drawn that line, because consultees check it.
How far should the search radius extend?
There is no radius in the Regulations, so it is set per topic and agreed at scoping. Transport follows the modelled network, landscape follows the zone of theoretical visibility, ecology follows habitat connectivity for the species present, and air quality follows the dispersion modelling domain. A single distance applied to every topic is difficult to defend.
What happens if a scheme is permitted after our cut-off date?
Agree the rule at scoping rather than improvising later. Normally a change note covers schemes that do not move any significance conclusion, and a formal addendum is produced where one does. Set a materiality threshold with the highway authority for re-running traffic modelling, otherwise each new permission in the district reopens the assessment.
Do allocations in the local plan count as committed development?
Allocations without an application are usually too uncertain for quantitative modelling, but they are rarely ignored altogether. The normal approach is a qualitative paragraph explaining the likely direction of effect and why numerical assessment would be speculative. Authorities promoting a growth area often ask for allocations to be modelled, so raise it at scoping.
Who can prepare a cumulative effects chapter?
The Environmental Impact Assessment Regulations 2017 require the Environmental Statement to be prepared by competent experts, and each topic chapter needs the relevant discipline. In practice the cumulative chapter is collated by the coordinating environmental consultant from the technical authors' residual effects tables, with each author confirming their own conclusions.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.