How Big a Conservatory Can Be Without Planning Permission
Most conservatories are built under permitted development, which means no application and no fee. What decides it is not floor area. It is how far the conservatory projects from the house, how tall it is, how high the eaves sit near a boundary, and how much of the plot is already built on. Every figure here is England.
Rear projection · single storey · England
4 m detached, 3 m attached 8 m and 6 m under prior approval
VerifiedPlanning Portal, England only. Checked 20 August 2026.
How large can a conservatory be without planning permission?
In England: up to 4 m deep on a detached house and 3 m on any other house, no more than 4 m high, with no more than half the land around the original house covered. Stay inside all of that and no application is needed.
Those are planning limits, and planning asks one question: what the building looks like and where it sits. Whether the Building Regulations apply at all is a separate test with a different number and a different body, settled at its owner: the Schedule 2 Class 7 exemption. The two get confused constantly, which is the subject of a section below.
If the number you came for is the price rather than the rule, work out what your conservatory will cost first, then check the size you had in mind against the table.
Every permitted development limit that touches a conservatory
England only, all from the Planning Portal, all checked 20 August 2026. All of them have to hold at once. Breaching one is enough to need an application, and it does not matter how comfortably you clear the others.
| Limit | Value | What it applies to | Named source |
|---|---|---|---|
| Rear projection, detached house | 4 m | Measured from the rear wall of the original house | Planning Portal |
| Rear projection, every other house | 3 m | Semi-detached, terraced and end-of-terrace | Planning Portal |
| Rear projection, detached, under Larger Home Extension prior approval | 8 m | Not permitted development. A prior approval process, not a free pass | Planning Portal |
| Rear projection, other houses, under Larger Home Extension prior approval | 6 m | As above | Planning Portal |
| Maximum height, single-storey rear extension | 4 m | Overall height of the new structure | Planning Portal |
| Maximum eaves height within 2 m of a boundary | 3 m | The limit most side-return conservatories meet first | Planning Portal |
| Height against the existing house | no higher | Not above the highest part of the existing roof, and not higher at the eaves than the existing eaves | Planning Portal |
| Side extension width | half | Half the width of the original house, single storey, and no more than 4 m high | Planning Portal |
| Plot cover | half | Half the land around the original house, counting every extension and outbuilding already there | Planning Portal |
| Position | behind | Nothing forward of the principal elevation, or of a side elevation where it fronts a highway | Planning Portal |
| Materials | similar | Exterior materials of similar appearance to the existing house | Planning Portal |
| Article 2(3) designated land | removed | All side extensions need permission, and so does any rear extension of more than one storey | Planning Portal |
| Householder planning application fee, England | no figure | Gap Our register holds no planning row | Not published here. Your local planning authority publishes it |
| Larger Home Extension prior approval fee | no figure | Gap Same absence | Not published here |
Source: Planning Portal, permitted development for householders, England, retrieved and checked 20 August 2026. Scotland, Wales and Northern Ireland run separate regimes and we hold no verified figures for them, so none of the numbers above should be read as British.
There is no price anywhere on this page, and that is deliberate. Our register carries no planning row at all, so we publish neither the householder application fee nor the prior approval fee. A statutory fee repeated from memory is the exact figure a homeowner quotes back to a council officer, and being confidently wrong in that conversation costs more than saying nothing. What would close the gap: the current published fee from a named authority, cited and dated, at which point it appears here with its source. In the meantime, note that the building control fee published elsewhere on this site is a different consent from a different body. It is not a planning fee and it is not a substitute for one.
A conservatory is not a special planning category
Which is why the limits above are the extension limits, not conservatory rules.
Planning law has no conservatory class. A conservatory built onto a house is an enlargement of that house, under Class A of Part 1, Schedule 2 of the GPDO 2015, the same class as a brick single-storey extension. The Planning Portal publishes one set of limits for both, and that set is the table above.
Two things follow. The first is that the conservatory is competing for an allowance the plot may already have spent.
Only half the area of land around the original house may be covered by extensions or other buildings.
The word doing the work is “original”. The allowance is measured against the house as originally built, not as you bought it, so a garage, an outbuilding or an earlier extension can already have spent part of it, whoever built them. On a plot already half covered, a conservatory needs permission at any size, and your local planning authority holds the property's planning history if you are not sure.
The second is that any page offering conservatory planning rules that differ from extension rules is describing something that does not exist. Where conservatories do get special treatment is the Building Regulations, which is the next section.
30 m² is a building regulations number, not a planning one
The 30 m² figure is real, well known, and nothing to do with planning permission. It is the floor-area ceiling on the Building Regulations exemption. Planning does not measure floor area at all: it measures projection, height, eaves and plot cover, and none of those four is an area. So the two tests disagree in both directions, routinely:
- Under 30 m² and still needs planning permission. A 5 m wide by 3.5 m deep conservatory on a semi-detached house is 17.5 m², comfortably inside the exemption. Its 3.5 m projection is outside the 3 m limit, so it needs an application.
- Permitted development and still outside the exemption. A conservatory can sit inside every limit in the table and still lose the Building Regulations exemption on the day the separating door is removed or a radiator is run off the house boiler. Neither of those is visible from the garden, so neither is a planning matter.
The arithmetic is ours, shown so you can check it: 5 m × 3.5 m = 17.5 m². The exemption and its five conditions are set out on the building regulations page linked at the top of this one. We are not restating them here, because two pages describing the same conditions in slightly different words is how a site starts contradicting itself.
Twelve by twelve, ten by ten, and the trouble with feet
Conservatories are shopped for in feet. Every planning limit is in metres.
This is not pedantry. The gap between the units is where most accidental breaches happen, because the common imperial depths land either side of the 3 m line and nobody converts them at the kitchen table. One foot is 0.3048 m, so:
| Depth in feet | In metres | Detached, 4 m limit | Every other house, 3 m limit |
|---|---|---|---|
| 8 ft | 2.44 m | Inside | Inside |
| 10 ft | 3.05 m | Inside | Outside, by 5 cm |
| 12 ft | 3.66 m | Inside | Outside |
| 14 ft | 4.27 m | Outside | Outside |
Conversions are ours at 0.3048 m per foot, rounded to two decimal places, shown so you can repeat them. The 4 m and 3 m limits are Planning Portal, England, checked 20 August 2026.
A 12 ft by 12 ft conservatory is one of the sizes that recurs most often in the search results we surveyed, and it is 3.66 m deep. On a detached house that is permitted development. On a semi or a terrace it is not, and no amount of narrowing the conservatory changes that, because the limit is on projection and not on area. The fix is depth. The 3 m limit is 9 ft 10 in, so a plan drawn at 9 ft 10 in rather than 10 ft is the difference between an application and none.
Which styles run into the limits first
Style is a planning question before it is a taste question, because the limits bite on shape. A lean-to takes its depth straight off the rear wall, so it meets the projection limit first and nothing else. A Victorian or Edwardian conservatory buys floor area by widening rather than deepening, which is often how to stay inside 3 m on an attached house.
A P-shape is the one to watch: a rear section and a side return joined together, and the side return is judged on the side extension rules, single storey, no wider than half the original house, eaves under 3 m within 2 m of the boundary. On Article 2(3) land that side return needs permission whatever its size. What each shape costs has a different owner: Victorian, Edwardian, lean to and P shaped costs.
Where on the plot it can sit
Position is the limit people find out about last. Nothing may go forward of the principal elevation, which rules out the front, and nothing forward of a side elevation fronting a highway, which quietly rules out much of many corner plots. Within 2 m of a boundary the eaves are capped at 3 m, the limit a boundary-hugging side return meets before any other.
Underneath all of it is a question planning never asks: what you are building on. Ground conditions, levels and drainage decide where a conservatory can physically go as much as the GPDO does, and they are priced at their owner under conservatory base cost.
Put a number against the size you are allowed to build
Six questions, roof condition first, phone number last. They live on the calculator, not on this page.
use the Conservatory Cost Calculator
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Changing the roof later is a different class
Everything above is about putting a conservatory up. Replacing the roof of one you already have is a separate question with a separate answer, because a roof alteration is not an enlargement and does not sit in the same class. It has its own limits and exceptions, answered at its owner: do you need planning permission to change a conservatory roof.
The roof job also brings in a consent this page never touches. A conservatory that loses its translucent roof usually becomes notifiable building work: different body, different application, and the only fee in this area we do publish. That is set out at who signs the work off. To compare what installers charge before going near either regime, compare local conservatory roof installers and ask each which consents they are taking responsibility for.
Questions people ask first
How large can a conservatory be without planning permission?
Do you need planning permission for a conservatory?
Is a 3m by 3m conservatory permitted development?
What counts towards the half-the-land limit?
My house is in a conservation area. What changes?
Are these limits the same across the UK?
Sources for this page
All retrieved and checked 20 August 2026.
The full list, with what each source is trusted for, is on our source list. For the money side of the decision rather than the rules, see what a conservatory costs. Checked 20 August 2026, next check due 20 November 2026.
Find out what yours costs
Six questions, about sixty seconds, and an estimate built from published UK figures with every source shown. Then up to four local installers can quote you, if you want them to.