Privacy and overlooking: justifying separation distances

There is no national overlooking separation distance in English planning. The 21 metre figure that appears in objection letters and refusal reasons comes from local design guidance, most of it descended from a small number of county design guides written decades ago, and it is guidance rather than a rule. Knowing that changes how you argue the point: the question an officer has to answer is whether the proposal causes unacceptable loss of privacy, and the distance is one piece of evidence towards that answer rather than the answer itself.

The proposal that fails is usually the one that treats the number as a test to be passed. The proposal that succeeds shows how the design handles the relationship.

Where separation distances come from

Most authorities publish a householder design guide or a residential design supplementary planning document containing a set of distances. The common figures are roughly 21 metres between directly facing habitable room windows, and roughly half that between a habitable room window and a blank elevation or a boundary.

They originate in low-density suburban layouts of two-storey houses on level ground, and they work reasonably well for that. Applied to a three-storey townhouse terrace, a mansard flat conversion or a sloping site, they produce results that nobody designing the street would recognise as sensible.

Check the status of the document before you rely on it or argue against it. An adopted supplementary planning document carries weight as a material consideration. A draft guide sitting on a council website unadopted for six years carries considerably less.

The detailed mechanics of window-to-window measurement are set out in separation distances between facing windows.

Why they are guidance rather than rules

National policy asks for a high standard of amenity for existing and future users. It does not specify distances, and the National Design Guide talks about the qualities of good places rather than setting numeric separation standards.

So a scheme falling short of a local distance is not automatically unacceptable. What the applicant has to show is that the actual privacy relationship is acceptable, and inspectors have accepted reduced distances where the design deals with the issue through orientation, screening or level changes.

The reverse also holds. A scheme comfortably exceeding 21 metres can still cause an unacceptable relationship if a raised terrace looks straight down a neighbour's garden.

Be careful with the word rule in correspondence. Once an objector has been told there is a 21 metre rule, every subsequent explanation sounds like special pleading, and the officer ends up defending a position they never took. Describe it as guidance from the outset and the conversation is easier.

Angled views, oblique windows and screening

Direct facing relationships are the easy case. Most real sites are oblique, and the oblique case is where the argument is won.

Draw the actual sight lines in plan. Take the window position, the sill height and the reveal depth, and plot the cone of view into the neighbouring property. A window set back 400 mm in a deep reveal, angled 30 degrees away from the neighbouring boundary, has a very different effect from a flush window facing squarely across.

Section drawings matter as much as plans where levels change. A proposal on ground a metre higher than the neighbour reads quite differently from the same proposal on level ground, and the section shows it in a way no distance figure can.

Existing screening is evidence, but weak evidence on its own. A mature hedge can be removed by the neighbour at any time, so officers discount it. Built screening that forms part of the permission, such as a fin wall or a solid balustrade, counts because it is secured.

Balconies and terraces as the harder case

A window frames a view. A terrace invites occupation, movement, noise and sustained presence, and officers treat the two very differently.

Four design responses work, in descending order of reliability.

1. Move the terrace to a position where it looks over the applicant's own land or over a street.
2. Set the terrace back from the parapet so the sight line into the neighbour's garden is cut by the building's own edge.
3. Provide solid screening to the flanks at a height that blocks a seated and standing view, integrated into the design rather than bolted on.
4. Restrict the use of the roof area by condition, which authorities accept with reluctance because it is hard to enforce.

The fourth option is the weakest and is often refused as a solution. A condition preventing use of a flat roof as a terrace relies on somebody reporting a breach, and officers know how that goes.

Obscure glazing and non-opening conditions

Obscure glazing is the standard fix for a secondary window in a flank elevation, usually secured by a condition requiring the window to be obscure glazed to a specified level and non-opening below a stated height.

Specify the level rather than writing "obscure glazing". Obscuration levels run on a scale, and a low level of obscuration still permits recognisable shapes. Which level to choose in which situation is covered in choosing an obscure glazing level.

The design objection to obscure glazing is that it produces rooms with no outlook, which is a poor result for the occupant. Use it for bathrooms, stairs and secondary windows. Do not use it to make a principal habitable room acceptable, because an officer assessing internal living conditions will pick it up, often alongside the Daylight and Sunlight Assessment.

Designing out overlooking rather than conditioning it

The strongest submissions solve the problem in the plan. Stagger the blocks so windows do not align. Put circulation and service rooms on the sensitive elevation. Use a single-storey element as a buffer. Angle the building on its plot.

These moves cost nothing at concept stage and are almost impossible to retrofit. A scheme arriving at the pre-application meeting with the windows already aligned across a 14 metre gap has a problem that screening will only partly solve.

And be honest in the Design and Access Statement about the relationships you have accepted. An applicant who identifies the tightest relationship on the site, explains the distance, and shows what was done about it is far more persuasive than one who leaves the officer to find it.

Evidence that persuades a case officer

Five things, and they are not expensive to produce. A plan with measured distances between the relevant windows, labelled with what room each serves. Sections through the tightest relationship. Sight line diagrams for the oblique cases. Photographs from the neighbouring boundary showing the existing situation. A short written note tying them to the local guidance and explaining any departure.

Officers are reasonable about departures that are explained and unreasonable about departures they discover. That is the whole of it.

One honest caveat. Where an objector engages their own consultant, the argument can move onto rights of light, which is a civil matter with its own tests and has nothing to do with the planning assessment of privacy. Keep the two separate in correspondence, because conflating them confuses everybody and helps nobody.

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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.