Daylight baseline choice when the site is already cleared

When a site has been cleared, the daylight baseline cleared site question decides the result before any modelling starts. Assess the proposal against open sky and almost any building will show large reductions to neighbouring windows. Assess it against the building that stood there and the same proposal may show modest change. Both are defensible positions, and the choice of baseline is the most common point of dispute in a daylight and sunlight case on a cleared site.

The answer is not to pick one. It is to report the primary baseline that the guidance supports, then show the alternatives as clearly labelled scenarios so the decision maker can see the difference.

Why the baseline choice changes everything

The BRE guidance on site layout planning for daylight and sunlight works by comparison. A neighbouring window's vertical sky component, or its daylight distribution, is calculated for the existing condition and again for the proposed condition, and the proportional change drives the assessment. The commonly applied figures, 27 per cent vertical sky component and a retained ratio of 0.8, both depend on an existing value.

On a cleared site the existing value is at its theoretical maximum. A window facing an empty plot may have a vertical sky component in the high twenties. Put a four-storey building opposite and the figure drops steeply, and the retained ratio falls well below 0.8 even though the proposal is no taller than its neighbours.

Run the same calculation against the three-storey warehouse that was demolished eighteen months earlier and the existing value may already be in single figures, so the proposal's additional effect is small.

Same building, same window, two completely different conclusions. Which is why a report that gives one figure without naming the baseline is close to useless.

Assessing against the cleared condition

This is the primary baseline, and the reason is simple: it is the physical condition that exists. The guidance compares the proposal with what is there, and a decision maker assessing effects on a neighbour's amenity is concerned with the change that neighbour will experience.

Councils and objectors will press for this baseline, and they are entitled to. An occupier who has enjoyed open sky for two years has a real amenity position, whatever its origin.

Two refinements make the cleared-site case fairer to the applicant. First, report absolute values alongside ratios, because a drop from 29 per cent to 24 per cent reads very differently as a ratio of 0.83 than as five percentage points. Second, say how long the site has been cleared, since a plot cleared last month and one cleared a decade ago sit differently in the planning balance.

Assessing against the building that stood there

The demolished-building scenario is a legitimate and useful additional analysis, provided it is built on evidence rather than recollection.

What makes it credible:

• Measured survey information for the former building, or a topographic survey carried out before demolition.
• Approved drawings from a planning or building control file, with the reference quoted.
• Dated aerial or street-level photography showing the building's height and footprint.
• A statement of what has been assumed where the record is incomplete, and a sensitivity test on that assumption.

What makes it fail is a massing model reverse-engineered from a photograph with no dimensional control, presented as if it were survey data.

The weight this scenario carries depends heavily on why the site was cleared. A building demolished because it was structurally unsound, or cleared under a prior approval years before the scheme was conceived, is part of the site's ordinary history. A building demolished shortly before an application, where the effect was to improve the daylight baseline, invites the obvious inference, and inspectors are alert to it.

Where a lawful fallback supports a baseline

A stronger version of the same argument rests on what could lawfully be built now, rather than on what used to stand.

An extant unimplemented planning permission on the site, within its time limit, gives a genuine comparator. So does a permitted development right that would allow a building of a given envelope. The test the courts apply to a fallback is whether there is a real prospect of it being carried out, which is a question of evidence rather than theory, and the Court of Appeal has set out how that is assessed.

Where a real fallback exists, modelling it is worthwhile. It shows the decision maker the daylight effect the neighbour cannot prevent, which puts the proposal's additional effect into proportion. Report it as a fallback scenario, state the permission reference or the permitted development class, and set out why the fallback is deliverable.

Where no real fallback exists, do not dress up a theoretical one. An inspector who concludes that a fallback is unrealistic tends to discount the rest of the analysis along with it.

Policy-compliant notional baselines

In dense urban areas, a third scenario is sometimes modelled: a hypothetical building on the site that complies with the development plan's height, massing and separation policies. The logic is that a neighbour cannot reasonably expect better than a policy-compliant development on an allocated or otherwise developable site.

Used carefully, this is informative. It answers the question an officer often asks, which is whether the scheme is worse for neighbours than a reasonable alternative would be.

Used carelessly, it becomes circular. A notional baseline built to the maximum of every policy parameter at once is not a realistic scheme, and modelling it proves only that a large building affects daylight. If the notional case is used, constrain it to a plausible development that respects the plan's design policies as a whole, state every assumption, and present it as a sensitivity test rather than as the baseline.

Local plan policies vary in how they incorporate the BRE figures, and some fix on ratios in ways that make the baseline choice decisive, which is covered in how local plan amenity policies use BRE 209.

Stating the baseline so the report survives scrutiny

Put the baseline question in its own short section near the front of the Daylight and Sunlight Assessment, not buried in the methodology appendix.

1. State the physical condition of the site, with the date it was cleared and the evidence for that date.
2. Identify the primary baseline as the existing cleared condition, and say so plainly.
3. List the additional scenarios modelled, each with its evidential basis: the former building, any extant permission, any permitted development fallback, any notional policy-compliant case.
4. Give results for each scenario in the same table format, with absolute values and retained ratios side by side.
5. Draw the conclusion from the primary baseline, then explain what the additional scenarios add to the planning judgement.

Reporting it this way removes the argument. An objector cannot claim the assessment hid the cleared condition, and the applicant is not confined to a baseline that overstates the effect.

Where the objection is coming from a neighbour rather than from the council, the same transparency helps, and objecting on daylight grounds sets out what carries weight from the other side of the counter.

One further point often missed. Daylight loss during construction is a separate and temporary matter, assessed differently, and conflating it with the permanent assessment muddies both, as temporary loss of daylight during construction explains.

Daylight modelling needs a suitably qualified author and councils expect one. 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.