Overlooking distances and back to back separation

Back to back separation distances are set by local design guidance, not by national policy, and the figure most commonly used in England is around 21m between facing habitable room windows, with roughly 12m from a habitable room window to a blank flank wall. Those numbers are conventions rather than rules, they vary between councils, and several urban authorities have abandoned them for dense sites. A back to back separation distance is a starting point for a privacy judgement, and a scheme that fails the local figure can still be acceptable if the privacy argument is made properly.

Check the adopted document for the authority you are applying to. Carrying a figure from the last scheme is how layouts get refused.

Where separation standards come from

The 21m convention descends from post-war residential layout guidance, built on the idea that two facing windows about 21m apart, roughly 70 feet, give enough distance that detail inside a room cannot be read from the other.

It survives because it is easy to measure and easy to apply, not because it has been validated. National policy contains no separation standard at all, and the current National Planning Policy Framework, published on 17 August 2026, deals with amenity through design policy rather than numeric distances. The standards live in supplementary planning documents, residential design guides and some local plan policies, which is why they differ.

That has a practical consequence. The separation figure is a material consideration with the weight the adopted document gives it. Where it sits in an adopted local plan policy, departing from it needs justification against that policy. Where it sits in a non-statutory design guide, it carries less weight and a design-led argument can displace it.

Typical back to back and back to flank figures

The figures in common use cluster, and it is worth knowing the pattern even though the local document governs.

Two refinements appear in better-drafted guidance. Distances increase with height, because a third or fourth floor window looks down into a garden rather than across at a wall. And distances to a rear boundary are treated separately from window-to-window distances, because garden privacy and room privacy are different concerns.

Where the guidance gives a single figure with no gradation by height or context, expect officers to apply it mechanically, and plan the layout accordingly.

Angled and oblique views

Separation measured perpendicular between facing windows is the easy case. Most real layouts are angled, and that is where the arguments happen.

The principle most guidance adopts is that an oblique view is less intrusive than a direct one, so the required distance reduces as the angle between the two windows increases. Some documents set this out as a sliding scale, others simply say that oblique relationships are assessed on their merits.

Measure and draw it. A plan showing the sightline from the centre of each window, with the angle to the facing window annotated and the distance along that sightline stated, answers the question in one drawing. Where the angle takes the view past the edge of the facing window, say so and show the cone of vision.

The thing to avoid is a layout that technically achieves a separation figure along one axis while placing a window directly across a 9m gap at 45 degrees. Officers look at the plan, not the schedule.

Screening, obscure glazing and planting

Three mitigations, with very different levels of acceptance.

Obscure glazing with restricted opening above a stated height is widely accepted for secondary windows, bathrooms, stairwells and landings, and it can be conditioned and enforced. It is not accepted for a habitable room's principal window, because a bedroom with obscure glazing is a poor room and the mitigation defeats the purpose of the window.

Fixed screening, meaning a privacy fin, a louvred screen or a solid balcony upstand, works where it is a permanent part of the building and shown on the elevations. It has to be designed, not added as a note.

Planting is the weakest. Officers discount it in most cases, because trees and hedges can be removed, die, or be pruned by whoever owns them, and because deciduous screening does nothing for half the year. Planting supports an argument. It does not carry one.

Boundary fences at 1.8m deal with ground-floor overlooking adequately and do nothing at first floor.

Upper floor terraces and balconies

Terraces and balconies are the most common source of overlooking objections on small schemes, and they attract tighter treatment than windows.

The reason is use. A window is looked out of occasionally. A terrace is occupied, often for hours, with people standing at the edge looking down. So guidance frequently applies a greater separation to terraces, or requires screening to the sides, or restricts terraces on elevations facing existing gardens altogether.

Design responses that work: set the terrace back from the building edge so the parapet restricts the downward view, provide solid or louvred side screens at a height that blocks the oblique view into the adjoining garden, orientate the terrace towards the scheme's own space or the street, and where a flat roof could be used informally, specify it as non-accessible with no door onto it.

A roof terrace shown on a drawing with no screening and a garden 8m below will attract a condition at best.

Dense urban sites and relaxed standards

Several urban authorities, London boroughs in particular, have moved away from fixed separation distances, because applying 21m in a city centre would prevent development of the kind the local plan is seeking.

The replacement is a design-led assessment: what is the existing pattern of separation in this area, how are the windows arranged, what rooms are affected, is the overlooking mutual, and does the design manage it through orientation, window position, winter gardens, splayed reveals or screening. That assessment has to be written, with drawings.

Mutual overlooking matters. Two new blocks facing each other across a courtyard at 15m is a different proposition from a new block overlooking existing back gardens at 15m, because future occupants buy into the arrangement they can see and existing residents did not.

Where daylight is also at issue in a tight layout, the separation question and the daylight question interact, and courtyard schemes and daylight to the lower floors covers that side. Single aspect units often result from privacy-driven orientation, which is dealt with in single aspect flats and how officers treat them.

Evidencing privacy on a tight layout

Four drawings and a short note carry the argument, and submitting them pre-empts the objection rather than answering it later.

1. A privacy plan showing every facing window relationship with the distance and angle annotated, and the room use labelled on both sides.
2. Sections through the critical relationships showing the viewing angle from the window or terrace edge, including the effect of parapets, reveals and screens.
3. Elevations marking which windows are obscure glazed and restricted, with the sill height stated.
4. A context plan showing the existing separation distances in the surrounding streets, which is the evidence that makes a departure from the local figure defensible.

Then a short written assessment that names the local policy or guidance figure, states where the scheme meets it and where it does not, and explains the design response at each point where it does not. Where daylight and sunlight are also in play, keep the two assessments separate but consistent, since the Daylight and Sunlight Assessment uses different metrics, and loss of light objections are weighed in a different way, as set out in neighbour daylight objections and how officers weigh them.

This is general guidance, not legal advice; check the adopted local plan and design guidance for your authority, or take advice from a qualified professional, before relying on it.