Two storey rear extensions: the 3 metre and 7 metre limits
Two storey rear extensions are treated far more tightly than single storey ones under Class A. The 7 metre boundary rule defeats most suburban gardens, and there is no prior approval route around it.
A two storey rear extension is permitted development only if it projects no more than 3 metres beyond the rear wall of the original house and no part of it comes within 7 metres of the boundary opposite that rear wall. Both limits sit in Class A of Schedule 2 Part 1 to the Town and Country Planning (General Permitted Development) (England) Order 2015, and both have to be satisfied. The 7 metre rule is the one that catches people, because a typical suburban garden of 12 or 14 metres leaves very little room once the extension is added.
Measure the garden before paying anyone to draw anything.
What Class A allows above one storey
Class A permits the enlargement, improvement or other alteration of a dwellinghouse, and it treats extensions of more than one storey far more tightly than single storey ones.
A single storey rear extension can go to 3 metres on an attached house or 4 metres on a detached one, with the larger home extension prior approval route doubling those figures. That route is available for single storey extensions only, so it does nothing for a two storey scheme.
For anything above one storey the limits are fixed: 3 metres of projection, 7 metres of clearance to the opposite boundary, no higher than the highest part of the existing roof, and a roof pitch matched to the original so far as practicable. There is no prior approval route that relaxes any of them.
| Limit | Two storey rear extension |
|---|---|
| Maximum projection beyond the original rear wall | 3 metres |
| Minimum distance to the opposite boundary | 7 metres |
| Maximum height | Not exceeding the highest part of the existing roof |
| Eaves height within 2 metres of a boundary | 3 metres |
| Total ground coverage of all buildings in the curtilage | 50 per cent |
Measuring the 3 metre depth
The projection is measured from the rear wall of the original dwellinghouse, and original means the house as it was first built, or as it stood on 1 July 1948 if it is older than the planning system.
That single word undoes a lot of schemes. A 1970s semi that gained a 2 metre kitchen extension in 1995 has 1 metre of the allowance left, and it makes no difference that the extension was built by a previous owner or that it has planning permission of its own. The measurement runs from where the original wall was, not from where the current one is.
Where the original rear elevation was not a straight line, for instance a house with an original back addition or outrigger, the relevant rear wall is the one the extension projects beyond, and the analysis gets fiddly. Get the original footprint from the council's planning history, historic Ordnance Survey extracts or the deeds before designing around an assumption.
Measurement is external, to the outer face of the new wall, and it includes the thickness of any external insulation or cladding.
The 7 metre boundary rule
No part of a two storey extension may come within 7 metres of any boundary of the curtilage that is opposite the rear wall of the house.
Two points about how that works. The boundary in question is the one facing the rear wall, so on an irregular plot it may not be the one you think of as the back fence. And the 7 metres is clear distance from the extension to the boundary, not from the original house, so the effective garden requirement is 7 metres plus the depth of whatever you build.
Run the arithmetic for a common case. An original rear wall with 13 metres of garden behind it, extended by 3 metres, leaves 10 metres to the boundary, which passes. The same house with 9 metres of garden leaves 6 metres after a 3 metre extension and fails, so the projection has to drop to 2 metres to clear the rule.
There is no flexibility here, no relaxation for an agreement with the neighbour, and no allowance for a garden that slopes or steps. A scheme that misses by 200 millimetres needs planning permission in exactly the same way as one that misses by 3 metres.
Height, roof pitch and materials
The extension must not exceed the height of the highest part of the roof of the existing house, and where it sits within 2 metres of a boundary the eaves height is capped at 3 metres, which effectively rules out a two storey extension close to a side boundary.
Roof pitch has to match the original dwellinghouse so far as practicable where the enlarged part has more than one storey. A flat roofed two storey box on a house with a 40 degree pitched roof does not meet that condition, and councils do enforce it. A pitched roof matching the main house, or a hipped roof following the original hip, is what the condition contemplates.
Materials must be similar in appearance to those of the existing house. Similar is not identical, and a reasonable brick match on a 1930s property is accepted, but a render finish on a brick house is not similar in appearance and takes the works outside the class. The same test applies to replacement windows and other alterations where an Article 4 direction is in force.
Side facing windows and obscure glazing
Any window in a wall or roof slope forming a side elevation of the enlarged part, at first floor level or above, has to be obscure glazed and non-opening unless the opening part is more than 1.7 metres above the floor of the room it serves.
Both halves matter. Obscure glazing alone does not satisfy the condition if the window opens below 1.7 metres, and a top hung opener at high level does not satisfy it if the glazing is clear.
Specify the obscurity level on the drawings. Councils responding to a complaint will ask what was fitted, and a note saying "obscure glazing to level 3 or above, fixed shut below 1.7 metres above finished floor level" answers it. The condition applies for as long as the extension exists, so replacing the glass later with a clear unit is a breach.
Where the right disappears
Class A is withdrawn or narrowed in several situations.
On article 2(3) land, which covers conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites, extensions of more than one storey at the rear are not permitted development at all. Cladding is also excluded there, and side extensions lose the right.
Article 4 directions remove rights on a street by street or area basis, and are common in conservation areas and in some estates. Listed buildings keep Class A in theory, but almost any external alteration to a listed building needs listed building consent, and that is a separate offence to carry out without.
Flats and maisonettes have no Part 1 rights at all. Neither do houses created through certain prior approval routes, where the permission itself removes them, and many modern estates carry a condition on the original permission withdrawing Class A rights. Read the decision notice for the estate before assuming. Similar traps apply to converting a garage to a habitable room.
If any doubt remains, apply for a lawful development certificate for proposed development under section 192 of the Town and Country Planning Act 1990. It is the only formal way to confirm that the works are lawful, and a purchaser's solicitor will ask for it in five years' time.
When a full application gives a better result
Householders often squeeze a design to stay inside Class A and end up with a worse house.
A full householder application allows a deeper extension, a different roof form, a larger opening to the garden and a proper relationship between the new rooms and the existing plan. It costs a fee and eight weeks, and it brings neighbour consultation, but on a plot that fails the 7 metre rule it is the only route anyway.
The judgement turns on how the scheme reads to the case officer. Two storey rear extensions on semi-detached and terraced houses are assessed against the 45 degree rule in plan and section and against the council's householder design guidance, and a projection of 3 metres at first floor level beside a neighbour's rear window will struggle whatever the permitted development position. A staggered design, a reduced first floor projection or a pitched roof falling away from the boundary answers the objection.
Where the scheme goes in as an application, a short Planning Statement setting it against the adopted local plan and the design guidance helps the officer write the report. For a view on which documents your own site will need, enter your postcode on PlanScope.
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
How deep can a two storey rear extension be without permission?
Three metres beyond the rear wall of the original dwellinghouse, measured externally to the outer face of the new wall. The larger home extension prior approval route that doubles the single storey allowance applies only to single storey extensions, so it gives no help at all above one storey.
How is the 7 metre boundary rule measured?
It is the clear distance from the extension to the boundary of the curtilage opposite the rear wall, not from the original house. So a garden needs 7 metres plus the depth of the extension. A rear garden of 9 metres allows a projection of only 2 metres before the rule is breached.
Does a previous extension count against my allowance?
Yes. The measurement runs from the rear wall of the original dwellinghouse, meaning the house as first built or as it stood on 1 July 1948. An extension built by a previous owner, even one with its own planning permission, reduces what is left. Check the council's planning history before designing.
Can I build a flat roofed two storey extension under Class A?
Not on a house with a pitched roof. Where the enlarged part has more than one storey, the roof pitch must match that of the original dwellinghouse so far as practicable. A flat roofed box on a house with a pitched roof falls outside the class, and councils do enforce that condition.
Are two storey rear extensions permitted development in a conservation area?
No. On article 2(3) land, which includes conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites, rear extensions of more than one storey are excluded from Class A entirely. Cladding and side extensions also lose the right on that land.
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.