Daylight and sunlight in a section 73 amendment
Varying a condition under section 73 creates a fresh permission, which reopens the daylight and sunlight assessment. Whether the baseline is the existing situation or the consented scheme decides what the numbers mean.
A section 73 application to vary a condition produces a new planning permission, and a new planning permission means the daylight and sunlight effects are assessed again. That catches teams who assumed a minor material amendment would be a paper exercise. Move a building line by 600mm across an eight-storey elevation and the neighbour's vertical sky component moves with it.
The question that decides a section 73 daylight assessment is which baseline the comparison uses. Get that wrong and the report either overstates the harm, by ignoring what has already been consented, or understates it, by ignoring what is actually on the ground.
Why an amendment reopens the assessment
Section 73 of the Town and Country Planning Act 1990 allows an application for permission to develop land without complying with conditions attached to an earlier permission. If granted, the result is a fresh permission sitting alongside the original, which remains in existence.
Because it is a fresh permission, the authority assesses the development it authorises rather than only the change. In practice officers focus on the difference, but they are entitled to consider the whole scheme, and a neighbour who objects on daylight grounds will be entitled to have that objection considered.
Two boundaries on the power are worth remembering. A section 73 permission cannot alter the description of development, following the Court of Appeal's decision in Finney in 2019, so an amendment that changes what the permission is for needs a different route. And section 73 cannot be used to extend the time limit for implementation, so the new permission carries the original commencement deadline.
The Levelling-up and Regeneration Act 2023 inserted a new section 73B allowing variation where the effect would not be substantially different from the existing permission. Check the commencement position on gov.uk before relying on it, because the route has been brought into force in stages.
Choosing the baseline for comparison
Three candidate baselines exist and they answer different questions.
| Baseline | What it measures | When to use it |
|---|---|---|
| Existing built situation | The total effect of the development on neighbours | Always, as the primary BRE comparison |
| Consented scheme | The incremental effect of the amendment | Where the original permission is extant and implementable |
| Part-built situation | The effect from where construction has reached | Where a scheme is under construction and partly complete |
The BRE guidance assesses against the existing situation, and that comparison belongs in every report. Presenting only the consented baseline is the commonest criticism of section 73 daylight reports, because it hides the cumulative effect from a neighbour who has never seen a formal assessment of the scheme as a whole.
The consented baseline is legitimate as a fallback, and it is often the more informative figure for the officer. Its weight depends on whether the original permission could actually be built: is it extant, have the pre-commencement conditions been discharged, has it been implemented, and is the developer in a position to build it if the amendment is refused?
Where construction is underway, say so and show it. A scheme at fifth-floor slab level has a fallback that is not theoretical, and the officer report should record that.
Present both comparisons side by side and let the decision-maker weigh them. A report that chooses one and hides the other invites a request for further information at week six.
Small massing changes with large effects
The amendments that cause trouble are rarely the ones anyone flags in the covering letter.
Floor-to-ceiling height increases are the classic. An extra 150mm per storey, requested by the contractor for services, is 1.2m at the top of an eight-storey block, and the effect at the upper windows opposite is not proportionate to the change.
Others that routinely move the numbers:
- Moving a building line outwards, even by half a metre, on an elevation close to a boundary.
- Adding balconies, which obstruct the windows beneath them as described in balconies and overhangs and daylight loss below.
- Roof-level plant enclosures, lift overruns and photovoltaic arrays that raise the effective height.
- Changing from a recessed to a flush façade, which removes the light that reached a neighbour past a set-back.
- Substituting solid balustrades for glazed ones.
- Relocating or reducing the size of windows in the proposed scheme, which changes internal daylight rather than the effect on neighbours, and is assessed against the illuminance-based approach for new interiors.
Screen the amendment early. A quick vertical sky component run on the two or three most exposed neighbouring windows, before the design is fixed, costs little and tells you whether you have a problem.
Re-consultation and neighbour expectations
A section 73 application is publicised in the ordinary way, with a site notice or neighbour notification and the usual 21-day representation period.
That produces a predictable pattern. Neighbours who did not engage with the original application, often because they had not moved in yet, engage with the amendment. They are frequently unaware that a permission already exists, and they read the amendment as the whole proposal.
Two responses that help. Write the covering letter so that a neighbour can understand what is already permitted and what is changing, with a simple comparison drawing rather than only a schedule of amendments. And offer to meet where the affected property is a single household rather than a block.
Do not overstate the fallback in public-facing material. Telling neighbours that a worse scheme could be built is accurate in some cases and reads as a threat in most.
Conditions carried across to the new permission
The new permission has to carry forward the conditions of the original, other than the one being varied, and this is where careless drafting creates work for years.
Check three things on the draft decision notice before it is issued:
- That conditions already discharged on the original are reflected as discharged, or drafted to acknowledge the approved details, rather than re-imposed as pre-commencement requirements.
- That the approved drawings condition lists the correct revision numbers for the amended scheme, and not a mixture of old and new.
- That any condition requiring compliance with a submitted daylight report refers to the version accompanying the section 73 application.
Also check the commencement condition. Because section 73 cannot extend the time limit, the new permission should reflect the original deadline, and a notice that restates a three-year period from the new decision date is wrong and will be relied on by somebody later.
Where neighbouring windows could not be surveyed internally for the amended assessment, make sure the assumptions used are stated in the report and reflected in any condition, following the approach in modelling neighbouring rooms when access is refused.
When a fresh application is the better route
Section 73 is not always the quicker or less costly option.
Use a fresh full application where the change alters the description of development, where the cumulative effect of several amendments has moved the scheme substantially from what was approved, where the original permission is close to its commencement deadline, or where the daylight effects on neighbours have changed enough that the authority would want to assess the scheme afresh in any event.
The practical test is what the officer will have to do. If the report will have to reassess the whole scheme, a section 73 saves nothing procedurally and leaves you with two permissions and a drafting problem.
A non-material amendment under section 96A is the other end of the scale, and it is a narrow power. Anything with a measurable effect on a neighbour's daylight is unlikely to be non-material.
Documenting the comparison clearly
The report should let an officer answer one question without doing arithmetic: is the neighbour worse off under the amendment than under what is already permitted, and by how much.
Give a single table per affected property with columns for existing, consented and proposed values, the ratio of proposed to existing, and the ratio of proposed to consented, for vertical sky component, daylight distribution and annual probable sunlight hours where relevant. Then a count of windows and rooms by outcome band, using the 0.8 threshold explained in the 0.8 relative test and when a loss is noticeable.
State the drawing revisions used for each of the three model runs. State whether the consented model was rebuilt or reused from the original assessment, and if reused, whether the surrounding context has changed since.
Then write a conclusion that says what changed, in plain terms, for each affected property. PlanScope can produce a first draft of that Daylight and Sunlight Assessment structured to these headings, which a qualified daylight consultant should model, check and sign off before submission.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
Does a section 73 application need a new daylight assessment?
Usually yes where the amendment changes massing, height or façade position. Section 73 produces a fresh permission, so the authority assesses the development authorised rather than only the change, and a neighbour objecting on daylight grounds is entitled to have that objection considered.
Which baseline should the assessment use?
Both. The BRE guidance assesses against the existing built situation, and that comparison belongs in every report. The consented scheme is a legitimate second baseline showing the incremental effect, with weight depending on whether the original permission is extant and capable of being implemented.
Can section 73 change the description of development?
No. The Court of Appeal confirmed in Finney in 2019 that a section 73 permission cannot vary the description of development. Section 73 also cannot extend the time limit for implementation, so the new permission carries the original commencement deadline rather than a fresh period.
Which amendments most often change the numbers?
Increases in floor-to-ceiling height compounded over several storeys, moving a building line outwards, adding balconies, roof-level plant and lift overruns, changing a recessed façade to a flush one, and substituting solid balustrades for glazed ones. Screen the two or three most exposed windows early.
What should the report table contain?
Existing, consented and proposed values for each affected window and room, with the ratio of proposed to existing and of proposed to consented, covering vertical sky component, daylight distribution and sunlight where relevant. Add a count of windows and rooms by outcome band against the 0.8 threshold.
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.