Assessing daylight against a consented scheme next door
An extant permission next door changes what your daylight results mean. Assess against the built situation first, then add the consented case and label both.
When a neighbouring site holds an unimplemented planning permission, the daylight baseline question is whether that unbuilt scheme counts as part of the existing situation. The practical answer is to assess against the built situation as the primary baseline, then present a second set of results with the consented scheme in place, and label both clearly. BRE 209 treats the existing situation as the starting point while recognising that permitted development on adjoining land may also be relevant, and an extant permission is in any event a material consideration the decision maker can take into account.
What goes wrong is presenting only the second set. Results that quietly assume a building that does not exist look like an attempt to flatter the scheme, and officers treat them that way.
Whether an unbuilt consent forms part of the baseline
Two readings are defensible and they produce different numbers.
The existing situation reading says the neighbours' windows currently enjoy the light they enjoy, and that is what your scheme will take from them. If the consented building is never built, the harm is real and permanent.
The future situation reading says the neighbouring owner can lawfully build and probably will, so comparing against a condition that is about to disappear overstates the harm your scheme causes.
Both readings matter to the decision maker, which is why the sensible submission contains both. The existing baseline tells the officer the worst case. The consented baseline tells them how much of that worst case is attributable to your scheme rather than to development already permitted.
Where the consented scheme would itself remove most of the light, say so plainly and show the figures. That is a legitimate point and it carries weight when it is presented transparently rather than buried in an assumption.
Checking the status and expiry of the neighbouring permission
Do this before any modelling, because the answer determines how much weight the second baseline can bear.
- Find the permission on the authority's online register and download the decision notice and the approved drawings. Model from the drawings, not from a planning statement description.
- Check the time limit. The default under section 91 of the Town and Country Planning Act 1990 is three years from the date of permission, though conditions sometimes vary it.
- Check whether the permission has been lawfully begun. A material operation under section 56 keeps it alive indefinitely, so a permission with a trench dug and a notice served is a much stronger baseline than one untouched.
- Check the pre-start conditions. A permission with several undischarged conditions and nine months left on the clock is closer to lapsing than its expiry date suggests.
- Check for a later section 73 or section 96A application, since the scheme you should be modelling may be a revision of the one originally approved.
Record the answers in the report with the application reference numbers. An officer who has to go and find the neighbouring permission themselves will assume the worst about why you did not include it.
A permission that has lapsed, or that is weeks from lapsing with no site activity, should not form a baseline at all. Mention it, and leave it out of the results.
Assessing with and without the consented scheme
Model three states rather than two.
The existing built situation. The existing situation plus the consented neighbouring scheme. And each of those with your proposal added. That gives four result sets and two comparisons, which sounds heavy and is actually the only way to keep the attribution clear.
Run the same tests throughout, meaning vertical sky component, daylight distribution and annual probable sunlight hours where the orientation calls for it, reported room by room. Do not switch methods between baselines. And keep the room naming and the window references identical across all four sets, because an officer comparing tables needs the rows to line up.
Where a room is served by more than one window, the treatment has to be consistent in both baselines, and that is easier to get wrong than it sounds. Our note on when a neighbour's room is served by two windows sets out the approach.
Where both schemes are under consideration together
This is the harder case. Two applications in the same authority, neither determined, each affecting the same receptors.
The authority has to decide them in some order, and whichever is determined first becomes part of the baseline for the second. That creates an obvious incentive to be first, and it is not a race worth running on daylight grounds alone, because an officer who notices the manoeuvre will assess cumulatively anyway.
The better approach is to propose a cumulative assessment openly. Ask the case officer, in writing, to confirm which baseline they want and whether they are treating the two schemes cumulatively. Then model what they ask for, plus the existing situation, and present both.
Cumulative effects on amenity space are a separate exercise, and sun-on-ground results across two schemes belong in an Overshadowing Study rather than in the window tables.
Agreeing the approach with the case officer
Raise it at pre-application. The question to put is narrow and officers can usually answer it quickly: does the authority accept the extant permission at number 12 as a baseline, and if so, do you want the existing situation reported as well.
Get the answer in writing and quote it in the report. Two benefits follow. The methodology stops being arguable, and if an objector challenges the baseline later, the report shows the approach was agreed rather than chosen.
Where the officer declines to commit, default to the existing situation as primary. It is the conservative choice, and a scheme that performs acceptably against the existing baseline does not need the second one at all.
Presenting two sets of results clearly
Formatting decides whether this is persuasive or confusing.
| Receptor | Existing baseline | With consented scheme | Proposal, existing baseline | Proposal, consented baseline |
|---|---|---|---|---|
| 12 Elm Road, living room | 32 per cent | 24 per cent | 22 per cent | 21 per cent |
| 12 Elm Road, bedroom | 29 per cent | 26 per cent | 25 per cent | 24 per cent |
The figures above are illustrative only. What the layout does is show at a glance that most of the loss in the first room is attributable to the consented scheme rather than to the proposal, which is the argument the table exists to make.
Then write two short paragraphs of conclusion, one for each baseline, and say which you regard as the primary comparison and why. Do not average the two. Do not present a single set of figures described as "cumulative" without saying what is in it.
A Daylight and Sunlight Assessment structured this way is longer than one baseline would need, and it survives scrutiny at committee and on appeal. Sensitive receptors such as hotel and care home bedrooms need their own treatment within it, which we cover in daylight to hotel and care home bedrooms.
Conditions that manage the sequencing
Developers sometimes ask whether a condition can deal with the uncertainty, requiring one form of development if the neighbouring consent is implemented and another if it is not. In practice that is very hard to draft enforceably, and a condition whose operation depends on a third party's decision on their own land will struggle against the tests in the Planning Practice Guidance on the use of conditions.
Two things do work. A condition securing mitigation within your own scheme, such as window positions, obscure glazing or balcony screening, which is enforceable because it concerns your land. And a condition requiring a revised assessment before a later phase is built out, on a multi-phase scheme where the phasing is within your control.
Beyond that, the honest position is to design to the existing baseline where the site can take it. Privacy and overlooking raise their own version of the same sequencing problem, which we look at in roof terraces and neighbour privacy in flatted schemes.
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 rather than legal advice, so check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Can I treat an unbuilt neighbouring permission as the baseline?
You can present it as a second baseline, but the existing built situation should remain the primary comparison. BRE 209 starts from the existing situation while recognising that permitted development on adjoining land may be relevant, and an extant permission is a material consideration. Submitting only the consented baseline looks like an attempt to flatter the results.
How do I check whether the neighbouring permission is still alive?
Download the decision notice from the authority's register, check the time limit condition against the default three years under section 91, establish whether a material operation under section 56 has been carried out, review how many pre-start conditions remain undischarged, and look for any later section 73 or section 96A application.
What if both schemes are undetermined at the same time?
Ask the case officer in writing which baseline they want and whether they will assess the two schemes cumulatively, then model that plus the existing situation. Whichever application is determined first becomes part of the baseline for the second, but an officer who notices an attempt to win that race will assess cumulatively anyway.
How many result sets should the report contain?
Four. The existing built situation, the existing situation plus the consented neighbouring scheme, and each of those with your proposal added. That keeps attribution clear, showing how much of the loss at each receptor comes from your scheme rather than from development already permitted next door.
Can a condition deal with the uncertainty about the neighbouring scheme?
Not usefully. A condition whose operation turns on a third party's decision about their own land is very hard to draft enforceably and sits badly with the tests on the use of conditions. Conditions securing mitigation within your own scheme, or requiring a revised assessment before a later phase you control, do work.
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.