Class D porches: the three square metre limit

Porch permitted development limits are three numbers and one exclusion. Under Class D of Part 1 of the General Permitted Development Order, a porch outside an external door of a house is permitted where its ground area measured externally is no more than 3 square metres, no part of it is more than 3 metres above ground level, and no part is within 2 metres of any boundary of the curtilage that fronts a highway. Break any one of those and the porch needs planning permission.

The numbers are unforgiving because they are absolute. A porch of 3.1 square metres is not a porch under Class D, and no amount of sympathetic design changes that.

The three limits, taken one at a time

Ground area measured externally means the footprint including the walls, not the internal floor you would stand on. A 2 metre by 1.5 metre porch measured outside the brickwork is exactly 3 square metres and leaves no room for error in setting out. Most builders work to 1.9 metres by 1.5 metres for that reason.

Height is measured from the ground level immediately adjacent to the porch to its highest point. A pitched roof on a porch approaching 3 metres is tight, especially where the ground falls away from the front door or where a step up to the threshold was built in.

The 2 metre highway distance is the one that stops most front porches on terraced streets. It is measured to any boundary of the curtilage which fronts a highway, and highway includes the footway and the verge, not only the carriageway. A house with a 1.5 metre front garden simply cannot have a Class D porch, whatever its size.

Take all three measurements on site before you order anything. Drawings scaled off a title plan are not accurate enough for a limit with no tolerance.

How the floor area is actually measured

Two details cause arguments with enforcement officers.

The first is whether existing structures count. If you are building a porch around an existing canopy support or over an existing step, the area is the area the new structure covers on the ground, taken to the external face.

The second is what happens with a porch that is not rectangular. A splayed or curved front is measured as the actual area enclosed, which usually means calculating it rather than multiplying two dimensions. Where the shape is unusual, draw it to scale and dimension the area on the drawing, so that the calculation is visible to anyone who looks at it later.

Keep the drawing, the setting-out photographs and the invoice. If a question arises years later, that file is what answers it.

Porches on flats, and why Class D does not apply

Part 1 of Schedule 2 applies to dwellinghouses. A flat or maisonette is not a dwellinghouse for these purposes, so none of Part 1 is available, including Class D. A ground-floor flat with its own front door and its own front garden has no porch right at all, and the reasons behind that are set out in this note on why flats and maisonettes have no Part 1 rights.

The same exclusion applies to a house that has been converted into flats, even where one occupier has exclusive use of the entrance. Buildings in other uses, including a house in multiple occupation that falls outside Class C3, need checking case by case.

Enclosing a recessed entrance

A recessed front entrance, common in interwar and 1960s houses, is inside the existing building envelope. Enclosing it with a new wall and door is not building a porch outside an external door, so Class D does not apply to it.

That work is usually an enlargement of the house, assessed under Class A of Part 1 instead. Class A prohibits extension beyond a wall forming the principal elevation where that elevation fronts a highway, so an infill at the front of a house facing the road normally needs planning permission. Where the recess is at the side or rear, Class A may cover it subject to its own limits.

This distinction gets missed frequently, because the finished result looks like a porch to everyone except the planning system.

Front boundary walls, levels and the things around the porch

A porch rarely arrives on its own. The associated works have their own rules.

• A new or raised front boundary wall next to a highway is limited to 1 metre in height under Class A of Part 2.
• A new or widened access onto a classified road is not permitted development and needs permission.
• Hard surfacing in a front garden carries a condition about porous materials or drainage to a permeable area within the curtilage.
• Altering ground levels to form a level threshold can change the height measurement for the porch itself.

Where the house is listed, listed building consent is needed for a porch regardless of the permitted development position, and in a conservation area the porch may be permitted development while other alterations around it are not.

Where a porch tips into an extension

Exceed 3 square metres or 3 metres in height and the structure stops being a Class D porch. It does not automatically become unlawful. It may still be permitted under Class A as an enlargement of the house, but Class A has its own limits and the principal elevation restriction usually defeats a front structure.

In practice, a front porch over the limits means a householder planning application. That application is straightforward: a location plan, existing and proposed elevations, a block plan and a short covering statement. Where the street has a consistent building line and a uniform frontage character, expect the officer to focus on that rather than on the size. A short Planning Statement that addresses the building line, the materials and the effect on the rhythm of the terrace is usually enough.

On designated land the calculus shifts, because character carries more weight and some other rights are already restricted. The general position on permitted development in protected areas is worth reading before assuming a porch will be uncontroversial in a conservation area.

Confirming the position before you build

Class D is unusual in that it is easy to comply with and easy to breach by a few centimetres. Where the porch is close to any limit, apply for a Lawful Development Certificate for proposed use or development under section 192 of the Town and Country Planning Act 1990 before starting.

A certificate does three things. It gives you a formal decision that the works are lawful. It creates a dated record with drawings attached. And it is the document a buyer's solicitor will ask for, which matters more than it seems on the day you build.

The fee is modest compared with a householder application, and the council determines it on the facts and the law rather than on planning merits, so a compliant scheme is granted.

This is general guidance, not legal advice. Permitted development rights can be removed by an Article 4 direction or by a condition on a previous permission, and a Lawful Development Certificate is the only formal way to confirm that works are lawful. Check the position with your local planning authority or a qualified professional before relying on it.

If your porch needs an application, enter your postcode on PlanScope to see which reports your site needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.