Daylight modelling against a consented but unbuilt scheme

When a neighbouring site holds a planning permission that has not been built, the daylight baseline becomes a choice rather than a fact. The default under BRE 209 is the existing built situation, because that is what the occupiers of the affected property have now. The consented but unbuilt scheme is a second scenario, reported alongside, and the weight it carries depends on how close that consent is to being implemented. Report both and let the decision-maker weigh them.

Which baseline the assessment should use

BRE 209 is written around the existing situation. Its criteria compare the light a window or an amenity space receives now with the light it would receive after the proposed development, and every threshold in the guidance is framed that way.

That is not an accident of drafting. Planning protects the amenity people actually enjoy, and a resident whose living room loses a third of its vertical sky component has lost it whether or not the site opposite has a permission on it.

So the primary assessment is against the existing built form. Anything else is an additional scenario. Getting that order right in the report matters as much as the numbers, because an assessment that leads with the consented baseline reads as an attempt to shrink the reported impact, even when it is not.

Treating an extant permission as an obstruction

The consented scheme scenario is still worth running, and on some sites it is the more realistic picture of the future.

Model the consented scheme from the approved drawings, not from a massing assumption. Use the approved plans, sections and elevations, check whether any non-material amendment or section 73 variation has changed the envelope, and state the application reference and the date of the permission in the report. A reviewer will check the reference.

Then say where the consent stands. Three facts do most of the work:

1. The expiry date of the permission, and whether the three-year commencement period has been extended or partly relied on.
2. Whether pre-commencement conditions have been discharged, which is a strong signal of intent and is a matter of public record.
3. Whether a material start has been made on site, which converts the consent from a possibility into a near-certainty.

A permission with discharged conditions, a demolition contract and a start on site is close to being existing built form. A permission granted four years ago with nothing discharged is close to being nothing at all.

Testing both scenarios and reporting each

The presentation that survives review is a single table per receptor with three columns of results: the existing value, the value with the proposed development against the existing baseline, and the value with the proposed development against the consented baseline.

That format makes the honest point visible. Where a receptor already faces a substantial loss from the consented scheme, your development's marginal effect may be small, and the table shows that without you having to argue it. Where the consented scheme is irrelevant to that particular window, the table shows that too.

Keep the criteria labels consistent. If a window meets the vertical sky component and no-sky line tests against one baseline and fails against the other, say so in plain terms in the same row rather than in a separate commentary section. The room-by-room question of which windows serve which space still applies, and our note on when a room is served by two windows covers how those cases are handled.

Where the consent may never be implemented

Consents lapse. Sites change hands. Values move, and a scheme consented in one market does not get built in another.

This is the honest weakness in any argument built on a consented baseline, and it should be stated rather than glossed over. An assessment that says "the consented scheme is assumed to be implemented" without qualification invites the obvious response: assumed by whom, and on what evidence?

Better to state the position as a conditional. If the consented scheme is built, the affected windows will see the results in column three regardless of this application. If it is not, column two is the position. Both are true, and the decision-maker chooses how to weigh them against the evidence you have given on implementation.

There is a related but distinct argument worth separating out. Where your own site has an extant permission, that is a fall-back position, and it supports a case that the comparison should be with what you could build anyway rather than with the empty site. That is a different argument from the neighbouring-consent baseline, and mixing the two confuses officers.

Cumulative effects with several consents

On a regeneration site with three or four live consents around it, the scenarios multiply quickly, and running every combination produces a report nobody reads.

Reduce it to three cases. Existing built form. Existing plus all consented schemes that are under construction or have a material start. Existing plus all extant consents whether started or not. That gives a lower bound, a realistic middle and an upper bound, and it is defensible.

State each consent in a schedule with its reference, date, expiry, implementation status and the height and position of the massing used. Where a consent covers only part of a site, model only that part.

Do not include allocations, pre-application schemes or emerging proposals in the massing. A site allocation is not an obstruction, and modelling one as if it were is a mistake an objector's consultant will enjoy finding.

Agreeing the baseline with the officer

This is a pre-application conversation, and half an hour of it saves a modelling cycle.

Ask three questions. Which baseline the authority expects as primary. Which neighbouring consents it wants included, since the case officer knows which of them are live and which are effectively dead. And whether the authority's retained daylight consultant has a preferred reporting format, because many do and matching it speeds the review.

Put the answers in an email and reproduce the substance of it in the methodology section of the Daylight and Sunlight Assessment. A baseline agreed in advance is very hard to reopen at committee. A baseline chosen unilaterally is the first thing a third-party consultant attacks.

Where amenity space and overlooking are also in play, the same agreed set of massing should be used for the Overshadowing Study and for any privacy analysis, which raises the questions covered in our piece on roof terraces and neighbour privacy in flatted schemes.

How the decision is usually reached

Officers and inspectors treat the existing situation as the starting point and the consented scheme as a material consideration whose weight varies with the likelihood of implementation. That is a straightforward application of section 70(2) of the Town and Country Planning Act 1990, which requires regard to be had to material considerations, and section 38(6) of the Planning and Compulsory Purchase Act 2004, which makes the determination plan-led.

In dense urban settings the practical outcome is often a judgement that some loss of daylight is acceptable because the area is already constrained, with the consented baseline used as supporting evidence that the transition was always coming. Inspectors have approached it that way, though appeal decisions are indicative of reasoning rather than binding precedent, and each turns on its own facts.

What tends to lose an appeal is not the choice of baseline but a failure to report the alternative. Give both and the argument is about weight. Give one and the argument is about your method.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Daylight and sunlight modelling is specialist work, so councils expect a suitably qualified author and professional review is strongly advised.

Enter your postcode on PlanScope to see which amenity and daylight reports your scheme is likely to need.