Separation distances and overlooking in local policy

There is no national separation distance in English planning. The 21 metres back-to-back figure that turns up in objection letters, committee reports and half the country's design guides has no basis in the National Planning Policy Framework, in the Town and Country Planning Act 1990 or in any statutory instrument. It comes from local supplementary planning documents, most of them descended from mid-twentieth century guidance, and its weight depends entirely on whether the council you are dealing with has adopted it.

For a developer that cuts both ways. A separation standard in an adopted document is a real hurdle. A separation standard someone remembers from another borough is not.

Where the numbers come from

The familiar set is 21 metres between facing habitable room windows, 12 metres or thereabouts between a habitable room window and a blank flank wall, and a reduced figure where a change in level or an oblique angle removes the direct relationship.

They exist because they are easy to apply. A planning officer with 30 applications on the desk can scale a distance off a site plan in seconds, whereas assessing actual overlooking takes judgement and a site visit.

The problem is that a rule optimised for speed produces poor outcomes at density. Applied literally in an inner urban context, a 21 metre standard rules out perimeter blocks, mews arrangements and courtyard housing that have worked in English towns for two centuries. Which is why the better-drafted local plans now treat the figures as a starting point rather than a requirement.

What the policy framework actually says

National policy asks for a high standard of amenity for existing and future users, and it asks for efficient use of land. Those two pull against each other, and neither resolves into a distance.

In London, policy has moved further towards a design-led approach. The London Plan asks for site capacity to be optimised through a design-led process and sets housing quality standards that address privacy through design rather than through a fixed separation. Boroughs vary in how far their own documents have caught up, so check the borough policy alongside the London Plan rather than assuming one has displaced the other.

Outside London the position varies by authority. Some local plans set distances in policy. Some carry them in a design guide adopted as a supplementary planning document, which carries less weight than the plan itself but is still a material consideration. Some have nothing, and the argument is run on general amenity policy.

Establishing which of those three you are in should be the first hour of work on any scheme where separation is likely to be an issue, and the answer belongs in the Planning Statement.

Arguing a reduced distance

Where the standard cannot be met, the case has to be made on design rather than on assertion. Measures that carry weight, roughly in order of how much:

• Oblique angles, so that windows do not face each other directly
• Changes in level between the two buildings
• Screening by existing or proposed planting, where it is evergreen and within the applicant's control
• Obscure glazing or high-level glazing to the affected rooms, secured by condition
• Winter garden or recessed balcony arrangements that limit the sightline
• Room planning, so that the affected windows serve bathrooms, stairs or kitchens rather than living rooms and bedrooms
• Boundary treatment and defensible space at ground level

What carries little weight is a promise of future planting on land the applicant does not own, or a statement that the relationship is common in the area without evidence.

Two things strengthen any of these. Sightline sections drawn from the affected windows, which show the geometry rather than describing it. And a survey of the existing pattern of separation in the immediate context, which shows whether the standard reflects the area or contradicts it.

Scale matters to the argument as well. A single pair of facing windows at 15 metres is a different proposition from 40 flats looking into 40 flats across a courtyard, and the assessment should count the relationships rather than describing them in general terms. Officers respond well to a schedule listing each affected window, the distance, the angle and the mitigation applied.

Overlooking is not the same as daylight

These get conflated constantly, and conflating them weakens both cases.

Overlooking is about privacy and is assessed through geometry, sightlines and room use. Daylight and sunlight are assessed through the criteria in BRE 209, using vertical sky component, daylight distribution and probable sunlight hours. A Daylight and Sunlight Assessment says nothing about privacy, and a separation distance says nothing about light.

A third question, outlook or the sense of enclosure, sits between them. The 45-degree and 25-degree rules of thumb found in many design guides are attempts to control it. They are crude but they are widely applied, so test the scheme against whichever version the council uses and be ready to explain the result. Where amenity space rather than windows is affected, the sun-on-ground test belongs in an Overshadowing Study.

Keeping the three separate in the submission, with a clear heading for each, makes the officer's report easier to write and reduces the chance that a privacy objection gets answered with a daylight table.

Conditions and what happens after consent

Where a reduced distance is accepted on the basis of mitigation, expect conditions. Obscure glazing to specified windows, to a stated obscuration level, retained in perpetuity. Restrictions on the installation of additional windows or roof lights, removing the relevant permitted development rights. Screening to be planted before occupation and retained.

Two practical points. Permitted development rights for a dwelling can be removed by condition, but the condition has to be justified and precisely drafted, and it will be tested if it is drawn too widely. And obscure glazing conditions need to state the level of obscuration and whether the window may open, because a top-hung opening above 1.7 metres is a different proposition from a casement at desk height.

Illustrative example: a courtyard scheme where facing habitable windows sit 15 metres apart against an adopted 21 metre standard. The scheme that succeeds shifts the upper floor windows off axis by around 1.5 metres so no two face directly, sets the top floor back, uses obscure glazing to the two remaining direct relationships, and shows the whole thing in sightline sections. The Design and Access Statement records the alternatives tested. The scheme that fails simply notes that the site is constrained.

Getting the ground work right early

Three things to establish before the layout is drawn. Whether the separation standard sits in the local plan, in a supplementary document, or nowhere. Whether the affected windows in neighbouring properties serve habitable rooms, which needs checking rather than assuming. And whether the neighbouring site is itself allocated or likely to be redeveloped, which changes how much weight the current relationship carries.

None of that takes long. All of it is harder to do after the drawings are fixed.

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.