Porches under Class D and the two metre highway distance
Class D has three absolute limits and no prior approval route. How to measure the ground area externally, where the 2 metre highway line falls, and when a full application is the better option.
A Class D porch permitted development right has three numbers in it and all three have to be satisfied. The ground area measured externally must not exceed 3 m². No part of the structure may be more than 3 metres above ground level. And no part of it may be within 2 metres of any boundary of the curtilage with a highway. Fail any one of them and the porch needs planning permission, however modest it looks.
Class D sits in Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 and permits the erection or construction of a porch outside any external door of a dwellinghouse. That last phrase does a lot of work, and it is the source of most of the arguments.
The three limits in Class D
The limitations are set out in paragraph D.1 and they are absolute. There is no prior approval route, no fallback and no discretion.
| Limit | Figure | Common mistake |
|---|---|---|
| Ground area, measured externally | 3 m² maximum | Calculating the internal floor area |
| Height above ground level | 3 metres maximum | Measuring from the threshold rather than the ground |
| Distance from a boundary with a highway | 2 metres minimum | Measuring to the kerb instead of the boundary |
The 3 m² figure is small. A porch 1.5 metres wide by 2 metres deep is 3 m² externally before the walls are counted, which in practice means a usable internal depth of about 1.6 metres on a 1.4-metre width. Anyone sketching something they can put a pram and a coat rack in is usually already over.
Measuring the ground area externally
Measured externally means to the outer face of the external walls, including any plinth, and including the part of the structure that sits against the house. Take the measurement at ground level on the finished external dimensions, not from the internal plan.
Two details decide marginal cases. A roof overhang beyond the walls does not count towards the ground area, because the limit is on ground area rather than roof area, but the overhang does count for the height limit and it counts for the 2-metre highway test if any part of the structure comes within that distance. And a porch with splayed or curved returns needs the actual enclosed area calculated rather than a bounding rectangle, which occasionally rescues a design.
The height limit is measured from ground level, and where the ground is not level the reference point is the highest part of the surface of the ground next to the building. On a sloping front garden this can lose you 200 millimetres before you start. The general approach to that measurement is set out in measuring height under Part 1 against adjacent ground.
What counts as a highway for the 2-metre test
A highway is a way over which the public has a right of passage. That is wider than most householders expect and it is not limited to roads a council maintains.
It includes the carriageway, the footway or pavement and any verge, because all of those form part of the highway. It includes a public footpath or bridleway running past the front of the property. It can include an unmade lane where public rights of passage exist. What matters for Class D is the boundary of your curtilage with that highway, which is normally the front edge of your garden, not the kerb line and not the edge of the tarmac.
So the sequence is: establish where your curtilage boundary is, measure back 2 metres from it, and anything the porch occupies on the highway side of that line takes the works outside Class D. On a terrace with a 1.5-metre front garden, no Class D porch is possible at all, which is why so many front porches on Victorian streets have full planning permission.
A private driveway shared with neighbours and carrying no public right of passage is generally not a highway, but this is a question of fact and the title deeds are not the answer. Where it matters, ask the highway authority for the extent of the publicly maintainable highway and the definitive map position for any footpath, and keep the reply.
Conservation areas, Article 4 directions and listed buildings
Class D carries no restriction for the designated land in article 2(3) of the Order, so a conforming porch is capable of being permitted development in a conservation area, a National Landscape or a National Park. That surprises people, and it is often the only permitted development right left on a heavily designated frontage.
Three things take it away. An Article 4 direction can remove Class D for a defined area, and many councils have done exactly that across conservation areas, so check the direction before relying on the right. A planning condition on the original permission can exclude permitted development, which is a live issue on estate housing and is covered in development contrary to a condition and article 3(4). And Class D applies to a dwellinghouse, which excludes a flat or a building containing flats.
Listed buildings are a separate matter entirely. Permitted development rights do not dispense with listed building consent, and a porch on a listed building affects its character as a building of special interest, so consent under the Planning (Listed Buildings and Conservation Areas) Act 1990 is required and is frequently refused on principal elevations.
Enclosing an existing recessed entrance
A recessed entrance that you want to glaze across at the front building line is not a porch outside an external door, because nothing projects outside the line of the house. Class D does not apply.
What usually does apply is Class A, as an alteration to a dwellinghouse, since the works do not extend beyond a wall forming the principal elevation. The conditions of Class A bite instead, including the requirement that the materials used in exterior work are of similar appearance to those of the existing house. Where the recess is in a side elevation that fronts a highway, the position changes again and the Class A limits on side elevations come into play.
This is the kind of question where an application under section 192 of the Town and Country Planning Act 1990 for a lawful development certificate for proposed works is worth the fee. It is the only formal way to confirm that works are lawful, and a certificate in the file is what a buyer's solicitor will want in ten years' time.
Building Regulations for a porch
Most porches are exempt from the substantive Building Regulations requirements, but the exemption is conditional and people lose it without noticing.
The exemption for a porch applies where it is at ground level, the floor area does not exceed 30 m², and the existing external door between the house and the porch is retained. Remove that door to make one continuous hall and you have created an extension in Building Regulations terms, which brings Part L fabric standards and the whole heat loss calculation with it.
Two requirements survive the exemption in any case. Glazing in critical locations has to be safety glass, and any electrical work is notifiable under Part P. A porch built around an external gas or electricity cupboard must keep its ventilation, and a porch across a protected escape route in a flat or a house in multiple occupation is a different question again.
When a full application is the better route
Class D is restrictive enough that a lot of sensible porches cannot use it. A householder application is eight weeks, carries a modest fee that is indexed annually, and gives you a design that works rather than one squeezed to 3 m².
Go the application route when any of these apply: the front garden is shallower than about 2.5 metres, the design needs more than 3 m², the roof pitch pushes past 3 metres, the house is listed, an Article 4 direction or a condition removes the right, or the property is a flat. On a designated frontage the application will be judged on the effect on the character of the area, and a short Planning Statement setting out the design response to the street rhythm does more work than any amount of justification about need.
One honest point about enforcement. A porch built outside Class D is a breach, and the time limits for enforcement action against unauthorised building works are being changed under the Levelling-up and Regeneration Act 2023, so do not treat an old rule of thumb as a plan. The current position on breaches of permitted development limits is set out in enforcement time limits for permitted development breaches.
Enter your postcode on PlanScope to see which reports your project is likely to need.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
How big can a permitted development porch be?
The ground area measured externally must not exceed 3 square metres and no part may be more than 3 metres above ground level. Measured externally means to the outer face of the walls, so a 1.5 by 2 metre footprint is already at the limit and the usable internal space is considerably smaller than people expect.
Is the 2 metre distance measured to the kerb or the boundary?
To the boundary of your curtilage with the highway, which is normally the front edge of the garden rather than the kerb. The highway includes the pavement and any verge, so on a terrace with a 1.5 metre front garden no Class D porch is possible at all.
Does a public footpath count as a highway for Class D?
Yes. A highway is a way over which the public has a right of passage, which includes public footpaths and bridleways as well as roads, pavements and verges. Where the status of an adjoining lane is unclear, ask the highway authority for the extent of publicly maintainable highway and the definitive map position, and keep the reply.
Can I build a Class D porch in a conservation area?
Class D carries no restriction for the designated land listed in article 2(3), so a conforming porch can be permitted development in a conservation area or National Landscape. Check for an Article 4 direction first, because many councils have removed the right across conservation areas, and listed building consent is required separately.
Do Building Regulations apply to a porch?
Most porches are exempt where they are at ground level, under 30 square metres and the existing external door is retained. Removing that door turns the porch into an extension for Building Regulations purposes. Safety glazing in critical locations and notification of electrical work under Part P apply regardless.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.