Daylight where the neighbouring site is consented but unbuilt

When the site next door holds a planning permission that has never been built, the daylight baseline stops being obvious. BRE guidance takes the existing situation as the normal starting point, so the primary assessment runs against the buildings that stand there today. But an officer weighing a daylight consented unbuilt scheme against yours will usually want a second set of results showing what happens if that permission is implemented, and an objector certainly will. Run both, present them separately, and say which one you regard as the realistic case.

The mistake is running only the one that suits the answer.

Which baseline the assessment should use

The existing condition is the baseline. That is what BRE guidance on site layout planning for daylight and sunlight is built around, because the test is about the effect of a proposal on the amenity people actually enjoy now.

A consented but unbuilt scheme changes nothing about that today. It does, however, create a foreseeable future condition, and a decision maker is entitled to take foreseeable circumstances into account as a material consideration. So the consented scheme belongs in the assessment as a second scenario rather than as a replacement baseline.

Say this explicitly in the Daylight and Sunlight Assessment. Where an assessment quietly adopts the consented massing as the baseline, an objector will point out that the numbers understate the loss against the real world, and the credibility of the whole report suffers for what is usually a defensible methodological choice badly explained.

Extant permissions and the weight they carry

Not every unimplemented permission deserves the same treatment. Weight follows likelihood of implementation, and there are questions that settle it.

How long is left on the permission. A consent with four years to run is a different proposition from one expiring in eight months. Whether conditions precedent have been discharged, because a scheme that has done none of that work in two years is not moving. Whether any material operation has been carried out, since a permission that has been lawfully implemented can be completed at any time. Whether the site is in the hands of a developer with a track record of building, or of a land trader. Whether the scheme is viable at current costs, which is often the real answer where a consent has sat unbuilt through a period of cost inflation.

State your view on these points and the reasons for it. An assessment that reports a consented scenario without commenting on the likelihood of it happening leaves the weighting entirely to whoever is arguing against you.

Where the neighbouring permission is itself for a site clearance and redevelopment, the related question of the mirror image baseline and existing obstructions usually arises at the same time.

Running the assessment on two scenarios

The structure that works is four models, not two.

The third model is the one people leave out, and it is the one that wins arguments. Where a receptor already fails against BRE criteria because of the consented scheme alone, your proposal is not the cause of that failure, and showing the effect of the neighbouring permission in isolation makes the point without having to argue it.

Report each scenario in its own table with its own commentary rather than interleaving them. Percentage retained figures for Vertical Sky Component and annual probable sunlight hours belong in the same row as the absolute values, since a room dropping from 8 per cent to 6 per cent reads very differently as a ratio and as a level.

Allocated sites without permission

A site allocation in an adopted local plan is a weaker proposition again. It establishes a principle and usually a broad capacity, and it rarely fixes a massing that can be modelled with any confidence.

Assessing against an allocation is normally not required, and a modelled allocation involves assumptions about height, footprint and window positions that nobody has approved. Where a council asks for it anyway, model a reasonable worst case built to the plan's own parameters, label every assumption, and present it as a sensitivity test rather than as a scenario carrying the same status as a consented scheme.

Where a development plan document or area framework does fix parameters, that is different, and those parameters should be used.

How officers treat a cumulative failure

A cumulative failure is not automatically a reason for refusal, and it is not automatically survivable either. What officers look for is whose scheme causes what.

Three positions come up. Where the proposal causes the failure and the consented scheme is immaterial, the case turns on the primary assessment. Where the consented scheme causes the failure on its own, the proposal adds little and the argument is about marginal harm. And where neither causes a failure alone but together they do, the question becomes one of sequencing and of whether the cumulative effect is acceptable in the context of a changing area.

That last point carries real weight in town centres and opportunity areas, where BRE guidance itself recognises that target values may be applied flexibly in dense urban contexts provided the reasoning is set out. Flexibility has to be argued from local context and adopted policy, not asserted. Presenting the reasoning so that a committee can follow it is a separate skill, covered in presenting daylight results a committee can read.

Sequencing when two schemes are live

Where both applications are undetermined at the same time, neither can assume the other. Assess against the existing condition, run the cumulative scenario on the other scheme as submitted, and say plainly which application was registered first.

Watch for the situation where your cumulative model uses a neighbouring scheme that is itself amended during determination. Fix the drawing reference and the revision number of the neighbouring scheme you modelled, and record the date you downloaded it from the public register. Otherwise the results are unreproducible, which an objector will notice.

One tactic worth considering on a constrained site is early engagement with the neighbouring applicant. Two schemes designed with knowledge of each other frequently perform better than two schemes designed in ignorance, and the massing adjustments that resolve a cumulative failure are usually small. Early testing of the geometry, as in obstruction angles and the early massing test, makes that conversation concrete.

Presenting both results clearly

Lead with the primary assessment. Give the cumulative scenario its own section with its own heading and a one-paragraph explanation of why it is included and what status you invite the decision maker to give it.

Four things make the difference in the written report. A plan showing the consented scheme's footprint and height alongside the existing buildings, so a reader can see what is being added. A statement of the drawing references and permission reference modelled. A short assessment of the likelihood of implementation with reasons. And a clear conclusion for each scenario separately, rather than one conclusion blending both.

Where the effect falls on gardens or amenity space rather than windows, an Overshadowing Study covers ground the daylight report does not.

Enter your postcode on PlanScope to see which amenity documents a scheme is likely to need, then have the modelling carried out by a suitably qualified consultant.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.