Double Storey Extension
Usually, yes. Permitted development does cover some two storey rear extensions, but the conditions are tight enough that most houses in built up areas fail at least one of them. Understanding which one you fail is the useful part, because Double Storey Extensions that go the application route are frequently better schemes than the ones squeezed into the permitted development box.
Here’s how to work out which position you’re in, in the order the tests actually apply.
Test One: Is Your Property Eligible at All?
Four situations end the question immediately.
Flats and maisonettes have no permitted development rights for extensions. Any extension to a flat needs a full application.
Listed buildings need listed building consent alongside any planning requirement.
Designated land removes the right entirely for multi storey rear extensions. This is the one that catches most London homeowners, and it’s covered below because it’s so commonly missed.
Previously extended houses may have used the allowance already. Every Class A measurement is taken from the original dwellinghouse as it stood on 1 July 1948, or as first built if later. Not as it stands today.
Test Two: Designated Land Rules Out Two Storey Rear Extensions
On article 2(3) land, a rear enlargement with more than one storey is not permitted by Class A at all.
Article 2(3) land includes conservation areas, areas of outstanding natural beauty, national parks and world heritage sites. Conservation areas are the relevant category for most of London and a lot of Surrey.
So if you’re in a conservation area, the answer is yes, you need planning permission, and no amount of redesign changes that. It’s a designation level restriction, not a dimension one.
That isn’t bad news in itself. Plenty of two storey extensions get approved in conservation areas on their merits. It just means the route is an application from the start.
Test Three: The 3 Metre and 7 Metre Rules
If your rights survive, these two limits apply together to any rear enlargement of more than one storey.
The extension must not extend beyond the rear wall of the original house by more than 3 metres. And no part of it can be within 7 metres of any boundary opposite that rear wall.
The 7 metre rule is the one that ends most urban schemes. Measured from the rear wall of your proposed extension to the rear boundary, you need 7 clear metres. If your garden is shorter than that once the extension is built, a two storey permitted development extension isn’t available.
On a typical London terrace with a garden under 12 metres, adding 3 metres of extension leaves you short. Worth measuring before reading any further.
Test Four: Heights, Eaves and the Boundary Trap
Three height conditions apply.
Eaves and ridge height must not exceed those of the existing house. Roof pitch on extensions higher than one storey must match the existing house as far as is practicable.
Then there’s the condition that quietly makes most two storey permitted development extensions impossible. Where any part of an enlargement sits within 2 metres of a boundary, the eaves cannot exceed 3 metres.
Think about what a two storey extension actually needs. A usable first floor room wants roughly 2.4 metres of ceiling height. Add the ground floor ceiling, the intermediate floor structure and the roof build up, and your eaves land somewhere around 5.5 to 6 metres.
A 3 metre eaves cap makes that geometrically impossible. So unless your extension sits more than 2 metres from every boundary, permitted development is off the table.
The Full Condition List
| Condition | Limit for multi storey rear extensions |
| Depth beyond original rear wall | 3 metres maximum |
| Distance from boundary opposite rear wall | 7 metres minimum |
| Eaves and ridge height | No higher than existing house |
| Eaves where within 2 metres of a boundary | 3 metres maximum |
| Roof pitch | Match existing house as far as practicable |
| Coverage of land around original house | 50 percent maximum, including outbuildings |
| Upper floor side windows | Obscure glazed, non opening below 1.7 metres |
| Balconies and verandas | Not permitted development |
| Materials | Similar in appearance to the existing house |
| Two storey side or front extensions | Not permitted development at all |
That last row matters. Class A covers rear enlargements of more than one storey. It does not cover two storey side extensions or anything projecting beyond the principal elevation. Both need a full application regardless of dimensions.
What Changes If You Need an Application
The council assesses the design rather than checking your measurements against a table. That’s the real difference, and it cuts both ways.
You lose the certainty of the permitted development route. You gain the ability to design what the house actually needs rather than what fits within a set of caps that were never drawn with your plot in mind.
Householder applications carry an eight week target determination period, running from validation rather than from submission. An incomplete drawing pack sits at validation before that clock starts, so the pack matters as much as the design.
Two storey schemes attract closer scrutiny on neighbour amenity than single storey ones, particularly on daylight and overlooking. Many councils assess daylight impact using the 45 degree approach, drawn from the centre of a neighbour’s nearest habitable room window, and some apply the BRE daylight and sunlight guidance on tighter plots. Local practice varies, so check your own council’s adopted guidance rather than assuming.
Upper floor windows are where privacy objections concentrate. Sill heights, obscure glazing and oblique orientation all resolve this, and they’re easy decisions in week two of design.
Why Most Two Storey Extensions End Up as Applications Anyway
Read back through the conditions and the pattern is clear. The 7 metre boundary rule assumes a long garden. The 3 metre eaves cap assumes generous space to the sides. The designated land exclusion covers a large share of London and Surrey housing stock.
Between them, those three conditions mean permitted development two storey extensions mostly suit detached houses on generous plots. Which is exactly the type of property least likely to need the constraint in the first place.
For everyone else, the honest answer is that an application is the route, and it’s worth approaching it as an opportunity rather than an obstacle. Architects for extensions spend most of their time on designs that were never going to be permitted development, and those schemes are usually the better buildings.
The Checks Worth Doing Before You Commission Anything
Four things, each of which takes minutes.
Measure your garden depth from where the new rear wall would sit to the rear boundary. If it’s under 7 metres, you have your answer.
Check conservation area status on your specific address, not your street.
Check for an Article 4 direction separately. These are different controls that often overlap, and a property can sit outside every conservation area and still have rights removed.
Pull your planning history through the council portal. Previous permissions sometimes carry conditions removing permitted development rights on that property, and previous extensions count against your 50 percent curtilage allowance.
Do those four and you’ll know which conversation you’re having before anyone draws a line.
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