Separation distances between facing windows
No national policy sets a privacy separation distance. Here is where the familiar figures came from and how to argue a scheme that falls below them.
The 21 metre rule is not a rule. There is no national privacy separation distance for windows, no statutory figure, and nothing in national policy that sets one. What exists is a family of numbers that migrated out of local authority residential design guides written decades ago, and which councils still apply because they are easy to measure and easy to defend at committee.
That does not make them irrelevant. A case officer with a policy that says 21 metres will apply 21 metres, and an appeal fought on the basis that the figure has no legal status will lose. The productive argument is about what the distance is for, and whether the relationship in front of you achieves it by other means.
Where the familiar figures come from
The usual set is 21 metres between directly facing habitable room windows across a rear boundary, and something around half that, commonly 10.5 or 12 metres, between a habitable room window and a blank flank wall or a boundary.
They come from post war local authority housing layout guidance, at a time when the typical case was two storey semi detached and terraced housing on generous plots. The geometry behind them is straightforward: at 21 metres, at normal storey heights, a person at one window cannot read detail at the other.
Some authorities have carried the figures into adopted supplementary planning documents. Others quote them in an unadopted design guide or apply them as officer practice without publishing anything. The weight they carry depends entirely on where they sit, and that is worth establishing at the start of any case.
Check the status before you argue about the number. An adopted development plan document has statutory weight under section 38(6) of the Planning and Compulsory Purchase Act 2004. A supplementary planning document is a material consideration. An unpublished internal convention is neither.
Why they are guidance rather than standards
National policy asks for good design and a high standard of amenity for existing and future occupiers. It does not prescribe how that is achieved, and it does not set distances.
The figures also assume a case that is increasingly rare: two storey houses, facing squarely, across level ground, with no intervening screening. Apply them mechanically to a four storey block on a sloping site facing a terrace at an angle and the answer they give is close to meaningless.
The other limitation is that distance alone does not measure privacy. A kitchen window at 15 metres facing a bathroom window is a different proposition from a living room facing a bedroom at the same distance. The rooms matter, the floor levels matter, and the angle matters more than either.
So treat the figure as a screening test. Where the scheme meets it, the issue is closed. Where it does not, the work begins.
Dense urban schemes and reduced distances
In town and city centres, the figures are routinely not met, and schemes are consented anyway. Urban blocks are built at separations that no suburban design guide would accept, because the character of the place is different and the alternative is not building.
The argument that works is contextual. Establish what the existing separations in the immediate area are, with measured examples from the surrounding streets, and show that the proposal sits within that range. A scheme proposing 16 metres in a street where the existing terraces face each other at 14 metres is proposing something normal for its context.
Then deal with the design. The same logic applies to daylight, where fixed numerical targets are relaxed in dense contexts on an evidenced basis, an approach set out in our note on alternative daylight targets in dense urban areas.
Officers and inspectors are receptive to this where it is evidenced and resistant where it is asserted. Photographs, measured plans and a short table of existing separations do more than three paragraphs of argument.
Oblique views and angled windows
Angle is the most underused tool in this area. Two windows at 12 metres, offset so that neither looks directly into the other, give better privacy than two windows squarely facing at 18 metres.
Draw the sightlines. A plan showing the cone of view from each habitable room window, with the angle to the neighbouring window and what actually falls within it, answers the objection in a way no distance schedule can. Include the vertical dimension in section, because a ground floor window looking up at a second floor window sees very little.
Design moves that create obliqueness: rotate the block, splay the window reveal, use an angled bay, set the window in a projecting fin, or move the opening along the elevation so it aligns with the solid between the neighbour's windows.
Where a direct view cannot be avoided, obscure glazing with a restricted opening is the fallback, and the specification needs to be right, as our note on how councils word obscure glazing conditions explains. Treat it as the last option rather than the first, because a habitable room behind obscure glass has lost its outlook.
Screening, planting and level changes
Physical screening works, with two caveats. It has to be permanent, and it has to be secured.
Planting is the weakest form. A hedge is deciduous or it dies or the next owner removes it, and inspectors discount planting that has not yet established. Where planting is part of the case, show the species, the height at planting rather than at maturity, and the management arrangement, and expect the officer to give it modest weight.
Built screening is stronger: a fin wall, a louvred panel, a solid balustrade upstand at balcony level, or a boundary wall of adequate height. Secure it by condition, including retention.
Level changes cut both ways. A scheme lower than its neighbour reduces overlooking from the new windows and increases overlooking into them. Where ground levels fall away, model the sightlines in section rather than assuming the drop helps.
Balconies deserve separate attention. A balcony is occupied for longer, at a more relaxed angle of view, than a window, and objections about balcony overlooking succeed more often than objections about windows at the same distance.
Evidence that supports a reduced distance
Assemble five things, and put them in the planning statement rather than in a separate technical annexe nobody reads.
- A measured schedule of window to window distances, by room type, for every affected relationship
- Plan and section drawings showing sightlines from each habitable room window
- A table of existing separations in the surrounding streets, measured from mapping and checked on site
- A description of the mitigation for each relationship that falls below the local figure, with the condition proposed to secure it
- A short statement of the rooms affected on both sides, because a landing window is not a living room
Then say plainly which relationships remain below the figure and why the residual effect is acceptable. Officers respond badly to statements that quietly omit the worst case, and they find it in the drawings anyway.
Where a Daylight and Sunlight Assessment is being prepared for the same scheme, keep the two documents consistent. Privacy and daylight are separate tests, and a section drawn for one should not contradict the section drawn for the other.
How inspectors treat the figures
Appeal decisions on this issue follow a recognisable pattern. The inspector notes the council's figure, notes that it is guidance, and then assesses the actual relationship: the angle, the levels, the rooms, the screening and the character of the area.
Schemes falling short of the figure are allowed regularly where the relationship is oblique, where there is a substantial level difference, where existing separations in the area are similar, or where the affected rooms are not principal living spaces. Schemes meeting the figure are refused occasionally where the relationship is unusually direct or the rooms unusually sensitive.
The honest uncertainty is that outcomes vary between inspectors, because this is a judgement rather than a calculation. What improves the odds is evidence about the specific relationship rather than argument about the general principle.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. Enter your postcode on PlanScope to see which amenity documents a scheme is likely to need. 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 the 21 metre rule a legal requirement?
No. There is no national privacy separation distance, no statute setting one and nothing in national policy that prescribes a figure. The familiar numbers come from post war local authority residential design guidance. Their weight depends on whether they sit in an adopted plan, a supplementary planning document or unpublished officer practice.
What separation do councils usually apply?
Commonly 21 metres between directly facing habitable room windows across a rear boundary, and around 10.5 to 12 metres between a habitable room window and a blank flank wall or boundary. Check the wording and status of the local policy, because the figures and the way they are measured vary between authorities.
How can a scheme justify a shorter distance?
By evidencing the actual relationship. Measured window to window distances by room type, plan and section drawings showing sightlines, a table of existing separations in the surrounding streets, and the mitigation proposed for each relationship that falls below the local figure. Angle and level difference usually matter more than the raw distance.
Does planting count as screening?
It carries modest weight. Inspectors discount planting that has not established, and a hedge can be removed by the next owner. Where planting is part of the case, show species, height at planting rather than at maturity, and the management arrangement. Built screening such as a fin wall or a solid balustrade upstand is far stronger and can be conditioned.
Are balconies treated differently from windows?
Yes, and more strictly. A balcony is occupied for longer and at a more relaxed angle of view than a window, so objections about balcony overlooking succeed more often at the same distance. Screening, orientation, upstand design and setting balconies away from the sensitive boundary all help more than adding metres.
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.