Do I Need Planning Permission for a Porch?
Three square metres is the planning limit and thirty is the Building Regulations one, and they get quoted at each other in the wrong order.
A porch is permitted development under Class D provided its ground area measured externally does not exceed 3 square metres, no part is more than 3 metres above ground level, and no part sits within 2 metres of any boundary of the curtilage with a highway. The right covers a porch outside any external door of a house, not only the front one. Miss any of the three and there is no fallback, because Class A does not permit anything beyond a wall forming the principal elevation, so the porch becomes a householder application. The 30 square metre figure often quoted is the Building Regulations exemption and is unrelated to the planning limit.
Usually not, provided it stays inside three square metres. A porch has a permitted development right of its own, Class D, and it turns on three numbers: a ground area measured externally of no more than 3 square metres, no part more than 3 metres above ground level, and no part within 2 metres of any boundary of the curtilage with a highway.
The number people quote at each other is usually the wrong one. Thirty square metres is the Building Regulations figure for a porch. Three is the planning figure, and a porch runs into it about ten times sooner.
Three and thirty
Two separate regimes, two separate numbers, and nothing connecting them.
The Building Regulations exempt a porch added at ground level whose floor area does not exceed 30 square metres, where the glazing satisfies the safety requirements of Part K, and where the porch stays thermally separate from the house, which for a porch means the existing external door between the two staying where it is and no house heating being run into the new space. Exactly 30.0 square metres is exempt. It is a generous figure that no porch has ever troubled.
Class D is the planning right, and 3 square metres is the whole allowance. So a porch can comfortably need planning permission while remaining exempt from the Building Regulations, which is the combination people find hardest to believe. It is also why “we didn’t need any approval for ours” is not evidence of anything.
Measured externally, and from the ground beside it
Both measurements are taken from somewhere slightly different from where people assume.
Externally means the outside face of the finished walls, so the thickness of the construction counts against you rather than being ignored. A cavity brick wall is around 300mm through, and on a structure this small that comes off every side at once. A porch offering 1.5 metres by 2 metres of usable space inside is already past 3 square metres once the brickwork is round it. A glazed frame on a low dwarf wall buys noticeably more room for the same allowance, which is the practical reason so many porches are built that way.
Height is measured from the ground next to the porch rather than from the doorstep, and front gardens around here are rarely level. Where the frontage falls away from the house, the measurement is taken at the lower point and the 3 metres arrives sooner than the drawing suggests. A roof pitched to match the main house uses it quickly.
Any external door, not only the front one
Class D is not a front-of-house right, which changes the arithmetic on the third number.
The right covers the erection of a porch outside any external door of a house. A porch over a back door or a side door is the same class, with the same three numbers, and it is a route people overlook because the word porch has come to mean the thing at the front.
It matters because the highway test usually stops binding once you go round the back. At the front, the 2 metre rule is measured from the boundary between your property and the highway, and highway includes the adopted footway beside the carriageway, not only the road surface. It also includes a public footpath or bridleway. The line that counts is your garden wall or fence, so a house with a 3 metre front garden has 1 metre of depth to work with and a house whose door opens onto the pavement has none. A back door on the same house is typically nowhere near a highway boundary at all.
| Class D limit | Measured from |
|---|---|
| 3 square metres of ground area | The outside face of the finished walls |
| 3 metres above ground level | The ground next to the porch, at its lower point where the frontage falls |
| 2 metres from a boundary with a highway | Your garden wall or fence, not the kerb; a footway, footpath or bridleway counts |
Miss one of the three and there is nothing underneath
Exceed any of the three limits and the porch does not become a slightly larger permitted development. It becomes an extension forward of the principal elevation, and there is no right to build one of those at all.
Class A, the right that covers rear and side extensions, excludes anything extending beyond a wall forming the principal elevation of the original house. That limb carries no highway qualifier. A separate limb deals with a wall that fronts a highway and forms a side elevation, and the two get merged constantly, which misleads anybody whose house is turned side on to the road.
The effect for a porch is a cliff rather than a slope. At 2.9 square metres you build next month. At 3.1 you are making a householder application, determined within a statutory eight weeks from validation, and what the case officer weighs is the street: the building line, the rhythm of a terrace or a matched pair of semis, and whether the addition dominates the house. Corner plots lose the side route as well, because the flank elevation there often fronts a highway too.
What removes the right, and what does not
One of these will surprise you, and it is the good kind of surprise.
A conservation area does not on its own remove Class D. A porch inside the three limits generally remains permitted development in a conservation area, which is unusual among the Part 1 classes and genuinely useful in the historic parts of the city. An Article 4 direction is a different matter, because front elevations are exactly what those directions are normally aimed at, and where one applies the porch needs an application. Directions are local to defined areas, so the only reliable check is against your own address with the council.
Listing does not remove the right either. It adds listed building consent as a separate requirement under separate legislation for anything affecting the building’s special interest, and a structure attached to the elevation that gives a listed building its public face engages that almost by definition. Unauthorised work there is a criminal offence rather than a planning irregularity.
What does remove the right outright: flats and maisonettes, which have no Part 1 rights, and a condition on the original planning permission. Estates built from the 1980s onwards very frequently had those rights stripped by condition, often specifically to keep open-plan frontages open. Separately, the title may carry a covenant against enclosing a front garden. Covenants are private law, and the council will grant permission for something your deeds forbid.
The practical answer
Measure the external footprint on the drawing rather than the room you are picturing, find the actual boundary with the highway rather than the kerb line, and check with the council whether the address still has its rights. Those three answers decide it, and none of them costs anything.
Where the porch is clearly permitted development, apply for a Lawful Development Certificate anyway. A porch is the most publicly visible thing most people ever build. A buyer’s solicitor looks at a photograph of the front, sees a structure newer than the house and asks the question, and the certificate turns that into a five minute conversation. The wider design and construction detail sits on our porch extensions page, and the class this right sits within is explained in our guide to permitted development rights.
These limits change from time to time and how they apply depends on your property and its planning history. Treat this as an explanation of the system rather than confirmation of what you can build.
Last reviewed August 2026.
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