Setting a daylight baseline where a neighbour holds consent
Where the neighbouring site holds a permission nobody has built, the existing condition may flatter your scheme or punish it. This sets out when a consented baseline is realistic and how to present both without inviting a double counting objection.
Where the adjoining site holds an unimplemented planning permission, the daylight baseline is a choice, and the choice changes the numbers more than any modelling decision you will make. Assess against the existing condition and your scheme may show material losses to windows that are about to be built out anyway. Assess against the consented scheme and you may show almost no effect at all, while the people living there today lose half their light. The defensible answer is usually to report both, label them clearly, and be explicit about which one the planning judgement should rest on.
This is a judgement call rather than a technical one, and officers treat it that way.
The existing condition is the default
Start there and stay there. BRE 209 is written around the condition of existing buildings, with vertical sky component, no-sky line and annual probable sunlight hours measured against what windows currently receive. The numerical targets are guidance applied flexibly to context, which the guide itself says plainly, and that flexibility is about site character and density rather than about swapping the baseline.
So the existing condition goes in the report in full, every time. A Daylight and Sunlight Assessment that reports only a consented baseline will be read as evasive, and an objector will produce the existing figures within a week.
When a consented scheme is a realistic baseline
The question is not whether a permission exists. It is whether it is going to be built. Evidence that supports a consented baseline:
- Pre-commencement conditions discharged, with reference numbers.
- A commencement notice, demolition under way, or site hoarding and enabling works.
- A section 106 agreement completed and payments triggered.
- A contractor appointed, or the consented scheme being marketed on the strength of the permission.
- A current, unexpired implementation period with time still comfortably in hand.
Evidence that undercuts it: a permission approaching the end of its three year period with nothing discharged, a scheme granted before a significant policy change that would not be granted today, or a site that has changed hands with the new owner promoting something different.
Where the evidence is strong, present the consented scheme as the primary baseline and the existing condition as context. Where it is weak, invert that. Where it sits in the middle, which is most of the time, present them in parallel and say so.
Lapsed, part-implemented and expired permissions
Three situations need separating.
A lapsed permission is irrelevant to the baseline. It cannot be built, and modelling it suggests an advantage the applicant does not have. Mention it in the planning history and move on.
A part-implemented permission is the strongest case for a consented baseline. Once a material start has been made within the time limit, the permission is implemented and the remainder can generally be completed without a further time limit. Model what is built, then what remains capable of completion, and distinguish the two in the drawings.
An expired permission that has been renewed or superseded needs the current consent modelled, not the original. Check the planning register for section 73 variations, because a varied scheme can be materially different in height or massing from the drawings the applicant originally circulated.
Presenting two baselines side by side
Tabulate them against the same criteria, window by window, so the officer can see what the assumption changes rather than having to work it out.
| Baseline | What it models | Use it to show |
|---|---|---|
| Existing | Buildings and windows as they stand today | The effect on current occupiers |
| Consented | The neighbouring permission as approved | The residual effect once that scheme is built |
| Part-implemented | Built works plus the lawful remainder | The realistic future condition on a live site |
Keep one set of modelling assumptions across all three: the same reflectance values, the same room depths, the same window assumptions, the same treatment of balconies and obstructions. If a reader can attribute a difference between tables to anything other than the baseline, the comparison is worthless.
Report the same criteria throughout. Vertical sky component against the 27 per cent reference and the 0.8 former value test, no-sky line area retained, annual probable sunlight hours against the 25 per cent total and 5 per cent winter references, and the 0.8 and 20 per cent reduction tests. Where overshadowing of amenity space is in play, run it in a separate Overshadowing Study using the 21 March sun path rather than burying it in the window results.
How officers weigh the alternatives
Case officers are weighing harm to living conditions against the benefits of the scheme, and the baseline question feeds directly into the harm side. In practice officers tend to do three things.
They anchor on the existing condition, because that is what the complaint will be about. They give weight to a consented baseline in proportion to the evidence of delivery, which is why the implementation evidence belongs in the report rather than in a covering letter. And they look at the character of the area, since the same percentage loss reads differently on a dense urban street than on a suburban cul-de-sac.
Local policy matters here more than national policy does. The Framework says little about numerical daylight standards, and the work is done by development plan amenity policies and supplementary guidance, which is worth reading closely because how local plan amenity policies use BRE 209 varies considerably between authorities. Some adopt the figures as thresholds, which narrows the argument sharply.
The double counting objection
Expect it, and answer it in the report rather than at committee. The objection runs like this: the applicant is using the neighbour's consent to excuse harm that their own scheme causes, so the occupiers lose light twice and nobody is accountable for either loss.
The answer is attribution. Show the loss your scheme causes to the current condition. Show the loss the neighbouring consent causes on its own. Then show the combined position. Three numbers, each attributed to a cause. An officer can then decide how much weight to give each, and an objector cannot claim the figures were hidden.
What fails is a single table against a consented baseline with a footnote explaining the assumption. That is the version that gets picked apart, and it is also the version that shows up in the daylight arguments objectors make when a scheme reaches appeal.
An illustrative case
Take a six storey infill on a street where the site opposite holds a permission for a five storey block, granted two years earlier, with the demolition condition discharged and the site cleared. Against the existing two storey workshops opposite, the proposal shows vertical sky component losses below 0.8 of former value at eleven windows. Against the consented block, nine of those windows already fall below the reference before the proposal is built, and the proposal adds a further small reduction at two. This example is illustrative, but it shows why the attribution matters: the honest conclusion is that most of the loss is caused by a scheme that is not the subject of the application.
Wording the conclusion
Write the conclusion so that it survives being quoted in isolation, because it will be. Name the baseline you rely on, state the evidence for it in one sentence, give the result against both, and say what the residual harm is in planning terms rather than in percentages alone.
Avoid the two failure modes. Do not conclude that the scheme complies because the neighbouring consent will absorb the loss. And do not bury a material effect on current occupiers in an appendix. Officers remember which consultants do that.
If you want the supporting pack scoped before you commission modelling, you can see which reports your site needs from the postcode and the constraints attached to it.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Councils usually expect a suitably qualified author for daylight and sunlight work, and professional review is strongly advised. 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 BRE 209 say which baseline to use?
BRE 209 is written around the existing condition and does not prescribe a consented baseline. It makes clear its figures are guidance rather than mandatory limits, to be applied flexibly to the context. The use of an existing plus committed baseline is established practice in development control rather than a rule in the guide, so it has to be justified on the facts.
Should the existing condition always be reported?
Yes. Report the existing condition in full, whatever else you add. It is the only baseline that describes what the occupiers currently receive, and officers and objectors will ask for it. Presenting a consented baseline alone reads as an attempt to hide the real effect, and it tends to be given short shrift at committee.
What makes an extant permission a realistic baseline?
Evidence that it will be built. A permission with conditions discharged, a commencement notice or demolition under way, a contractor appointed, or a developer actively marketing the consented scheme all point one way. A permission granted five years ago, with no conditions discharged and nothing on site, points the other, and should be reported as a sensitivity rather than the main case.
How do you handle a part-implemented permission?
Model what has actually been built plus whatever remains lawfully capable of completion, and say which parts fall into each category. A permission is generally implemented by a material start, so the remainder can be completed without a time limit. That makes a part-implemented scheme a far stronger baseline than an untouched one.
Is a consented baseline double counting the neighbour's loss?
Only if you use it to excuse an effect your scheme alone causes. The honest presentation separates the two: the effect of your scheme on the current occupiers, and the residual effect once the neighbouring consent is built. Keep both numbers visible and attribute each loss to the scheme that causes it.
What about a neighbouring site with an allocation but no permission?
An allocation in the development plan is weaker than a permission and rarely supports a baseline on its own, because the form and massing are unknown. Where a site allocation includes parameters or a design code, a sensitivity test showing the effect of a compliant scheme can be useful context. Do not present it as the baseline.
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.