Privacy and overlooking distances between dwellings
England has no national separation distance. The 21 metre figure comes from local design guidance, and knowing that tells you when it can be argued with and what evidence a departure needs.
There is no national overlooking distance standard in England. The 21 metres between facing habitable room windows that appears in hundreds of refusal reports comes from local design guidance, not from the National Planning Policy Framework, and an architect who treats it as a rule will design timidly in the suburbs and get refused in the city centre anyway.
What exists instead is a set of conventions that most councils have written into supplementary planning documents, applied with more or less rigidity depending on the context. Knowing where the numbers come from tells you when they can be argued with.
Where the numbers come from
National policy treats privacy qualitatively. The Framework and the National Design Guide expect development to provide an acceptable standard of amenity for existing and future occupiers, without setting a dimension.
The dimensions come from three places. Adopted local plan policies, which sometimes state distances and more often refer to a design guide. Householder design guides and residential design supplementary planning documents, which is where most of the numbers live. And the practice of the individual case officer, informed by what has been refused and allowed locally.
The 21 metre figure has a long history in English housing layout guidance, and it has survived largely because it is easy to apply. Its weakness is that it takes no account of levels, boundary treatment, orientation, the existing pattern of development or whether the windows in question serve a bedroom or a landing.
In denser urban contexts the position is different again. The London Plan takes a design-led approach and discourages the mechanical application of fixed separation distances, which is why borough practice varies so much and why a scheme at 14 metres can be acceptable in one part of a city and refused in another.
The distances councils use
These are the conventions you will meet most often. Treat them as the starting point in a negotiation rather than as a specification.
| Relationship | Distance commonly applied |
|---|---|
| Facing habitable room windows, rear to rear | 21 metres |
| Habitable room window to a blank flank wall | 10.5 to 13.5 metres |
| Habitable room window to a side or rear boundary | Around half the back-to-back figure |
| Single-storey relationships | Reduced, and sometimes not applied at all |
Two refinements matter. Most guides apply the distance between the facing elevations rather than between the windows themselves, and most increase it where either building is three storeys or more, because a second-floor window looks further into a garden than a first-floor one.
Levels change everything and are the most common reason a compliant distance still causes harm. A dwelling on ground that sits 1.5 metres higher than its neighbour overlooks at a distance that would be unobjectionable on the flat. Draw the section. A section through the relationship, with existing and proposed levels and the sightline marked, persuades officers in a way that a dimension on a plan does not.
Oblique and angled views
Direct facing views are the case the standards were written for. Most overlooking in practice is oblique, and most design guides treat it more leniently.
Where a proposed window is set at an angle to the neighbour's window or garden, the relevant question becomes whether a person standing at the window has a clear and sustained view into the private space rather than whether a line can be drawn between the two openings. Many guides apply the full distance only within a defined arc in front of the window and a reduced distance outside it.
Design responses that work on this are inexpensive and undramatic. Offsetting windows so they do not align. Angling a bay or an oriel away from the neighbour. Using high-level glazing where the sill sits above standing eye level. Placing a rooflight rather than a vertical window in a flank. Each of these is easier to justify than a plea that 16 metres should be enough.
Balconies and roof terraces are the harder case
A balcony is treated more seriously than a window and rightly so. Occupation is sustained, people look outwards rather than glancing, and the elevated position extends the view into neighbouring gardens.
Refusals cluster around a few arrangements. A roof terrace formed over a rear extension, looking along the rear gardens of a terrace. A side balcony on a corner plot overlooking the neighbour's garden at close range. A juliet balcony that is really a full balcony once the doors are open. A communal roof terrace on a flatted scheme with no screening at its edges.
The mitigation that officers accept is physical rather than contractual. Set the usable area back from the parapet. Provide fixed privacy screens of a stated height on the flanks, shown on the elevations. Use planters as a physical barrier rather than as a decorative gesture. Where a terrace cannot be made acceptable, propose a green roof or a maintenance-only area and say in the Design and Access Statement that amenity space is provided elsewhere.
A note on inherited overlooking. Where an existing relationship is already poor, that does not license making it worse, but it does change the weight given to a modest additional effect. Say what the existing situation is, with photographs.
Obscure glazing, fixed lights and what a condition can do
The standard mitigation for a problematic window is obscure glazing combined with restricted opening. A condition normally requires the window to be glazed with obscure glass to a specified privacy level and to be non-opening below a stated height, usually 1.7 metres above the internal floor level of the room it serves.
That wording is borrowed from permitted development. The conditions attached to Class A of Schedule 2 Part 1 of the General Permitted Development Order 2015 require upper-floor windows in a side elevation to be obscure-glazed and non-opening unless the openable parts are more than 1.7 metres above the floor of the room. Using the same formula in a condition keeps it precise and familiar.
The limits of the technique are real. Obscure glazing on a habitable room window reduces the quality of the accommodation you are creating, and a condition that obscures the only window to a bedroom is solving the neighbour's problem by damaging your client's. It also depends on retention: glass gets replaced, and the condition needs a retention clause and a reason. Our note on obscure glazing conditions and when they work goes through the wording and the failure modes.
Upper floor windows in extensions
The recurring householder case is a first-floor rear or side extension with a new window. Three things decide it.
- Which room the window serves. A bathroom or landing window can be obscure-glazed without loss. A bedroom window cannot, so it needs to be positioned rather than treated.
- What the window sees. Draw the sightline from a standing position to the neighbour's nearest habitable room window and to the nearest part of their garden that gets used.
- Whether the same accommodation can be lit another way. A rooflight, a high-level strip or a window in the rear rather than the flank will often serve the room and remove the objection.
Rear extensions raise the amenity question in a different form, because the harm complained of is usually enclosure and light rather than privacy, and our note on rear extensions to a terraced house and neighbour amenity deals with that relationship. The overbearing test is a separate consideration again, covered in our note on outlook and the overbearing test.
Arguing a departure from the standard
Councils do accept departures, and they accept them on evidence rather than on assertion. Five things carry weight.
A section through the relationship showing levels, existing boundary treatment and the actual sightline. Photographs from the neighbour's likely viewpoint, or from the closest publicly accessible equivalent. A plan showing the existing pattern of separation in the surrounding streets, which in a Victorian terrace is often well below 21 metres and demonstrates the local grain. A schedule of the design measures adopted to manage privacy, each shown on a drawing. And an honest statement of the residual effect, because an application that claims no effect at all is less credible than one that identifies a modest effect and explains why it is acceptable.
Where daylight and sunlight are also in issue, the quantitative work is a different exercise with its own methodology, and the Daylight and Sunlight Assessment should be commissioned from a suitably qualified consultant rather than approximated. Councils normally expect a qualified author for that work and professional review is strongly advised.
One honest uncertainty. Separation distances are applied with real inconsistency between authorities and sometimes between officers in the same authority, and the only reliable way to find out how yours applies them is to ask at pre-application and to read recent decisions on comparable sites.
PlanScope can draft the Design and Access Statement and the supporting amenity narrative in minutes, structured to UK planning policy. Enter your postcode on PlanScope to see which reports your project is likely to need.
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.
Frequently asked questions
Is 21 metres a national planning rule?
No. The National Planning Policy Framework and the National Design Guide treat privacy qualitatively without setting a dimension. The 21 metre back-to-back figure comes from local plan policies and residential design guidance, and it has survived because it is easy to apply rather than because it reflects every context.
What distance applies between a window and a blank flank wall?
Design guides commonly apply between 10.5 and 13.5 metres from a habitable room window to a blank flank wall, roughly half the back-to-back figure. Many guides increase the distance where either building is three storeys or more, because a second-floor window looks further into a garden than a first-floor one.
Does obscure glazing solve an overlooking objection?
Sometimes, and at a cost. A condition typically requires obscure glazing to a specified privacy level and no opening below 1.7 metres above internal floor level, borrowing the wording from Class A of the General Permitted Development Order. It damages the accommodation where the window serves a bedroom, and it needs a retention clause.
Why are balconies treated more strictly than windows?
Because occupation is sustained and elevated. People look outwards from a balcony rather than glancing, and the raised position extends views into neighbouring gardens. Set the usable area back from the parapet, provide fixed privacy screens of a stated height shown on the elevations, and use planters as a physical barrier.
How do I argue for a shorter separation distance?
With drawings and photographs. Provide a section through the relationship showing levels and the sightline, photographs from the neighbour's viewpoint, a plan of the existing separation pattern in surrounding streets, a schedule of privacy measures, and an honest statement of the residual effect.
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.