Consented baseline: assessing a neighbour's unbuilt scheme

Choosing the consented baseline for a daylight assessment changes every number you report, and it is the first thing to settle with the case officer rather than the last. Where the site next door holds a planning permission that has not been built, you have two possible baselines: the buildings that exist today, and the buildings that would exist if that permission were implemented. Assess against the existing situation and your scheme looks worse. Assess against the consented situation and it usually looks better, sometimes dramatically so.

The defensible answer is normally to report both, and to be explicit about which one you regard as the realistic condition.

The two baselines and why the choice matters

The BRE guide Site Layout Planning for Daylight and Sunlight (BRE 209, third edition 2022) sets numerical targets for vertical sky component, no-sky line and annual probable sunlight hours, and it applies most of them as a comparison between the existing and proposed values at a given window. The baseline is therefore inside every single figure in the report.

Take a rear window with a vertical sky component of 31% today. If a permitted but unbuilt block next door would take that to 22% on its own, and your scheme would take it from 31% to 20%, then your reported loss is either 35% against the existing baseline or 9% against the consented one. Both are true statements about the same window. Only one of them describes the harm your scheme actually causes.

That is the argument in a sentence, and it is why officers are rightly suspicious of a report that shows only the consented baseline.

Whether an unimplemented permission counts

An extant permission is a material consideration. It is not a fact on the ground. The weight it carries depends on how likely it is that the development will be built, and that is a matter of planning judgement rather than arithmetic.

Points that push the weight up: the permission is recent, it is within its time limit, it has been implemented by a material operation under section 56 of the Town and Country Planning Act 1990, conditions have been discharged, a demolition contract is live, or the site is in the same ownership as a developer with a track record of building out.

Points that push it down: the permission is close to expiry with nothing done, pre-commencement conditions remain outstanding, the site is marketed for sale without the consent being relied on, or the scheme is of a type and scale that the market no longer supports.

Say which of these apply. A report that asserts a consented baseline without evidence of deliverability invites the officer to disregard it entirely, and that is the worst outcome available to you.

Lapsed, expired and partly implemented permissions

A permission that has expired unimplemented is gone, and it should not form a baseline. It may still be worth a paragraph as planning history, because it shows what the authority once considered acceptable on that land, but it does not describe a future condition.

A partly implemented permission is more interesting. Where a material operation has been carried out within the time limit, the permission generally remains capable of completion without a further time limit, subject to any condition to the contrary and to the limits on abandonment. The practical question for your assessment is what the half-built condition means for massing: a completed substructure and no superstructure still casts no shadow.

Part implementation of a phased consent is the awkward middle case. If phase one is built and phases two and three are consented but not started, the honest baseline is built phase one plus a clearly labelled sensitivity test including the later phases.

Cumulative assessment with an adjoining site

Where two schemes sit side by side and neither is built, each applicant has an incentive to treat the other as absent. Councils in dense urban areas increasingly ask for a cumulative run, and in London the expectation is now routine on larger schemes.

Structure it as three scenarios rather than two.

1. Proposed scheme against the existing surroundings.
2. Proposed scheme against the surroundings including the consented adjoining development.
3. Proposed scheme plus the consented adjoining development, assessed together against the existing surroundings, to show the combined effect on third-party windows.

The third scenario is the one that answers the question a resident actually asks, which is what their kitchen will be like when everything is finished. Our note on roof extensions and light to a neighbour's rear window covers the small-scale version of the same problem.

How much weight a consented baseline carries

There is no policy rule that fixes the answer, and BRE 209 is explicit that its numerical targets are guidance to be applied flexibly according to context rather than mechanical thresholds. The 2022 edition strengthened that framing, which cuts both ways: it gives you room to argue that a small numerical loss is acceptable in a dense urban setting, and it gives the objector room to argue that a technical pass against a consented baseline conceals a real-world loss.

What officers respond to is a report that does the arithmetic honestly and then makes a judgement in plain words. Something like: the existing baseline shows losses beyond the BRE targets at four windows, the consented baseline shows compliance at all of them, the adjoining permission has 14 months to run with no material operation carried out, and on that basis the existing baseline should carry the greater weight.

You have just argued against your own client and kept your credibility. That is usually the trade worth making, because the alternative is a refusal reason you cannot defend at appeal.

Presenting two baselines without burying the answer

Put the existing baseline in the main results tables and the consented baseline in a parallel set, with the same window references, on facing pages. Do not merge them into a single table with a column heading that a reader can miss.

State the basis in the executive summary in one sentence. Identify the reference of the neighbouring permission, its decision date, its expiry date, and whether any material operation has taken place. Include a massing diagram showing the consented envelope in a distinct outline, so a case officer who reads nothing else can see what you have assumed.

Where an Overshadowing Study accompanies the daylight work, keep the baseline consistent across both, and say so. Inconsistent baselines between two documents in the same submission are the sort of thing an objector's consultant will find.

Where the choice changes the conclusion

The baseline decides the outcome most often in three situations. Infill plots between two consented but unbuilt blocks, where the existing condition is an open gap that will not survive whatever happens. Backland sites where the adjoining permission is for a rear extension that has been consented for years and never built. And cleared sites, where the existing baseline is a demolished building and the surroundings are already changing.

In each case the temptation is to pick the baseline that helps and move on. Resist it. A Daylight and Sunlight Assessment that presents both baselines, evidences deliverability and states a view is far harder to attack than one that quietly assumes the answer.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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