Daylight baselines: existing, consented or cumulative
Daylight tests are relative, so the baseline decides the result. Here is how to treat existing buildings, cleared sites, unimplemented permissions and committed schemes.
The baseline is the single input in a daylight assessment that a reviewer should check before anything else, because it is the one that can change a conclusion from acceptable to unacceptable without a line of the calculation being wrong. BRE guidance compares the proposed condition against the existing situation. What "existing" means on a site with a building due for demolition, a neighbouring plot with an unimplemented permission, or a cleared plot that had a warehouse on it last spring is a matter of judgement, and different assessors resolve it differently.
State the baseline, justify it, and where a second reading is arguable, report both. That is the whole of good practice, and it is skipped more often than it should be.
Why the baseline choice changes the result
Daylight measures are relative as well as absolute. Vertical sky component has an absolute reference figure, and the guidance also treats a reduction to less than 0.8 times the former value as the point at which a change becomes noticeable. The same relative test applies to daylight distribution and to annual probable sunlight hours.
Relative tests need a "former value". Set that former value low, by assessing against a cleared site, and almost any proposal passes. Set it high, by assessing against a two-storey building that is about to be demolished, and the same proposal may fail.
For a reviewer, that means the baseline is not a preliminary matter. It is the assessment.
Existing built condition as the starting point
The default is what is physically on the application site at the time of assessment.
Where a building is to be demolished as part of the proposal, the comparison is normally against that building as it stands, because the neighbouring properties currently experience the obstruction it creates. A Daylight and Sunlight Assessment that assesses a redevelopment against an empty site overstates the loss attributable to the new scheme, and one that assesses against a taller hypothetical building understates it.
Reviewers should check three things:
- The date of the survey or mapping used to build the existing model.
- Whether any demolition has taken place since, and if so, when and under what consent.
- Whether the existing model includes the building's actual massing, including any later extensions.
Note: on a long-vacant site where the building has been derelict for years, the physical condition is still the baseline. Disuse does not remove an obstruction from the sky.
Unimplemented permissions nearby
An extant permission on an adjoining plot is a material consideration, and it is not the baseline.
The distinction matters. The baseline describes what neighbouring occupiers currently receive. A consented but unbuilt scheme next door describes what they might receive in future, which is a separate question and belongs in a cumulative scenario rather than in the comparison.
Where the consented scheme is under construction, the position shifts. A building with foundations in the ground and a start on site that has lawfully implemented the permission is closer to a reasonable future baseline, and reporting it as an additional scenario is the safer course.
Ask the authority for its list of committed schemes rather than compiling one from the public register alone, because a permission granted subject to a section 106 that has not been completed is not a permission at all.
Cumulative assessment with committed schemes
Cumulative assessment answers a different question: what would a neighbouring window receive if this proposal and the other committed schemes were all built.
It is worth doing on any site where a regeneration area or a cluster of consents surrounds the application. It is also worth doing where the applicant controls adjoining land, because an assessment that ignores the applicant's own second phase invites an obvious objection.
| Scenario | What it compares | When to report it |
|---|---|---|
| Existing versus proposed | Current physical condition against the scheme | Always |
| Existing versus proposed plus committed | Current condition against the scheme and other consents | Where consents cluster around the site |
| Consented versus proposed | An extant scheme on the application site against the current proposal | Where the applicant already holds a permission and is seeking a variation |
The third row is the one that gets misused. Comparing against your own extant permission is legitimate where the question is the change between two schemes, and it should sit alongside the existing condition comparison rather than replacing it.
Sites cleared in advance of application
A site cleared shortly before an application is made is a recurring argument, and reviewers should treat it carefully rather than accusingly.
Buildings are demolished for many reasons, including structural condition, insurance and security. What matters for the assessment is whether the pre-demolition condition can be reconstructed from evidence: survey drawings, previous applications, photographs, aerial imagery.
Where it can be reconstructed, report both. The comparison against the pre-demolition building shows what neighbours were used to, and the comparison against the cleared site shows the change from the condition on the day of the application. Presenting only the second, on a site cleared three months earlier, is the sort of thing an inspector notices.
Where prior demolition was carried out under a separate consent granted some years ago, the argument for using the cleared site is much stronger, and saying so plainly is better than leaving the reader to work out the chronology.
Stating the baseline clearly in the report
A baseline section that survives review contains six things:
- A statement of which condition is treated as the baseline, in one sentence.
- The evidence for that condition, with dates.
- A note of any demolition, with dates and consent references.
- The list of committed schemes considered, with application references, and those excluded with reasons.
- The scenarios reported, and why each was chosen.
- A cross-reference to the geometry and assumptions schedule.
Put it near the front. A reviewer who has to reconstruct the baseline from an appendix starts from a position of suspicion.
Where the assessment supports a wider case, keep it consistent with the Townscape and Visual Impact Assessment, which will have made its own baseline decisions about the existing townscape. Two documents describing different starting conditions is an easy point for an objector.
How inspectors have approached baseline disputes
Appeal decisions are indicative rather than binding, and the pattern across them is consistent enough to be useful: inspectors look for a baseline that reflects what neighbours actually experience, and they are unsympathetic to an approach that appears constructed for advantage.
Two behaviours attract adverse comment. Presenting a single scenario where two were plainly arguable. And relying on an unimplemented permission as the baseline without addressing whether it is likely to be built.
The reviewer's job is to make sure neither is present before the report leaves the office.
One honest uncertainty: there is no settled convention on how much weight an unimplemented permission should carry, and practice varies between assessors and between authorities. Say which approach you took and why, and the disagreement becomes a matter for the decision maker rather than a flaw in the report.
PlanScope drafts the narrative and policy sections around a specialist daylight assessment, structured to UK planning policy, with modelled results left to a qualified assessor. Councils expect a suitably qualified author for daylight work and professional review is strongly advised. See how professional review and sign-off works, or browse the report types.
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
Should a redevelopment be assessed against the existing building or a cleared site?
Against the existing building, in most cases. Neighbouring occupiers currently experience the obstruction that building creates, and the relative tests in BRE guidance need a former value that reflects what they actually receive. Assessing against a cleared site overstates the daylight available before development and understates the effect of the proposal.
Can an unimplemented permission next door be the baseline?
It should normally be reported as an additional scenario rather than as the baseline. The baseline describes what neighbours receive now. A consented but unbuilt scheme describes a possible future, and its weight depends on how likely it is to be built. A permission subject to an uncompleted section 106 is not yet a permission at all.
When is a cumulative daylight assessment worth doing?
Where consents cluster around the application site, in a regeneration area, or where the applicant controls adjoining land and has a further phase in mind. Ignoring your own second phase invites an obvious objection. Ask the authority for its list of committed schemes rather than compiling one from the public register alone.
What if the site was cleared shortly before the application?
Report both readings if the pre-demolition condition can be reconstructed from survey drawings, earlier applications, photographs or aerial imagery. Presenting only the cleared-site comparison on a site demolished a few months earlier is the sort of thing an inspector notices. Where demolition happened years ago under a separate consent, the cleared site is the stronger baseline.
What should the baseline section of a report contain?
One sentence stating which condition is the baseline, the evidence for it with dates, a note of any demolition with consent references, the committed schemes considered and those excluded with reasons, the scenarios reported and why, and a cross-reference to the geometry and assumptions schedule. Put it near the front of the report.
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.