Porches: the 3 square metre and 2 metre limits

A porch is permitted development under Class D of Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 if it meets three limits: a ground area of no more than 3 m² measured externally, no part more than 3 metres above ground level, and no part within 2 metres of the boundary between the curtilage and a highway. Miss any one and it needs planning permission.

Three square metres is smaller than most people picture. It is roughly 1.5 metres by 2 metres, measured over the walls rather than inside them.

What Class D covers

The class permits the erection or construction of a porch outside any external door of a dwellinghouse. Any external door, so a porch over a side or rear door is within the class as readily as one over the front.

What it does not cover is anything that stops being a porch. A structure that encloses a large area, connects to a garage, or works as a small room is an extension, and it falls to be considered under Class A with its own limits on depth, height and eaves. That reclassification is not a technicality: a 4 m² glazed lobby fails Class D on area and then has to pass the extension limits instead, including the rule that nothing may extend beyond a wall forming the principal elevation fronting a highway.

Which is why most front porches on houses set close to the pavement need permission, whatever their size.

Three square metres, measured externally

Ground area is measured externally, taking in the walls, and it is the area of the structure rather than the usable floor inside it.

A porch with 100 millimetre cavity walls loses roughly a fifth of its internal space to construction on a small footprint, so a design drawn to 3 m² internally is over the limit before it is built. Draw it externally from the start, dimension the drawing, and show the calculation.

Two further points. Where a porch wraps around a corner of the house, the whole enclosed footprint counts, including the returns to either side of the door. And where a porch is built against an existing canopy or overhang, the area of the enclosed structure is what matters, not the covered area that existed before.

The 3 metre height limit

Height is measured to the highest part of the structure from ground level, not to the eaves. On a porch with a pitched roof that makes the ridge the controlling dimension, and 3 metres is not generous once a threshold, a door head, a lintel and a pitched roof are stacked up.

Ground level means the natural ground level immediately next to the structure, and where the ground slopes the measurement is taken from the higher part. A porch on a house approached up three steps loses height to the step rise.

The practical answer on a tight height budget is a shallow pitch, a lead flat roof with a modest parapet, or a mono-pitch running back to the house. Pitching a porch roof to match a steep Victorian gable rarely fits within the figure.

Two metres from the highway boundary

This is the limit that catches terraces and houses on narrow frontages, and it is regularly misread.

The measurement is from the boundary of the curtilage of the dwellinghouse with a highway, which is normally the front property line at the back edge of the pavement. It is not measured from the kerb, the carriageway or the centre of the road. So a house whose front wall stands 1.8 metres back from the boundary cannot have any part of a porch under Class D, even a shallow one.

Highway includes a public footpath or bridleway, which surprises owners of houses fronting an alley rather than a road. Where the frontage is that tight, the options are a rear or side porch, or a planning application for the front. A householder application is not a demanding process, and a short Planning Statement covering scale, materials and the street scene answers most of what the officer needs.

Flats, listed buildings and article 4 directions

Class D applies to dwellinghouses. A flat or a maisonette has no Part 1 rights at all, so any porch on a converted house in flats needs permission.

Listed buildings are a separate regime. Adding a porch to a listed building affects its character and needs listed building consent regardless of the planning position, and the application will need a Heritage Statement setting out the significance of the building and the effect of the proposal on it. Works within the curtilage of a listed building can also be caught.

Unlike side extensions and roof alterations, porches are not automatically removed on article 2(3) land, so a porch in a conservation area can be permitted development. But conservation area article 4 directions frequently do remove Class D, precisely because front doors and their surrounds define the character of a terrace. Check the council's article 4 map and the planning history for the house before assuming.

The same question arises for other frontage works, and rendering or cladding a house runs into the same directions.

Enclosing an existing recessed entrance

A surprising number of porch projects are not porches at all.

Where a house has a recessed entrance within the main building line and the work encloses it with a new front wall and door, nothing projects beyond the original wall. That is an alteration to the building rather than the erection of a porch outside an external door, and it is normally assessed under Class A as an enlargement, or under the alterations provisions, rather than under Class D. The 3 m² limit does not apply, which usually helps, but the Class A restriction on extending beyond a principal elevation fronting a highway may.

Where the recess is partly enclosed already, the analysis depends on the original form of the house, and the cumulative position matters too. Our note on extending a house that has already been extended explains how earlier works reduce what is left.

If there is any doubt, a lawful development certificate is the only formal way to confirm that works are lawful. Apply for a certificate for proposed use before starting rather than arguing about it afterwards.

Building regulations and the practical detail

Planning and building regulations answer different questions, and a porch can be exempt from one while needing the other.

Porches built at ground level are generally exempt from building regulations where the floor area is under 30 m², the glazing and any electrical work meet the relevant requirements, and the existing front door between the house and the porch remains in place. Remove that internal door and the porch becomes part of the heated envelope, which brings in the thermal elements requirements and changes the construction.

Three practical details decide whether the finished porch looks right. Keep the roof pitch and the eaves detail consistent with the house, because a shallow pitch on a steeply pitched terrace reads as an addition from fifty metres away. Match the brick bond and the mortar rather than the brick colour alone. And set the threshold level so that the porch floor sits with the existing entrance rather than stepping up into it.

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.