Rooflights, dormers and solar: what permitted development actually allows on a roof
Three different classes, three sets of numbers, and one measurement that almost every page in the country takes off the wrong roof.
Rooflights are permitted development under Class C, dormers under Class B, and solar panels under a different Part of the Order altogether. Class C allows 0.15 metres of projection, measured from the original roof rather than the roof you are looking at. Class B is not permitted on any protected land, conservation areas and National Parks included.
The short version
- The 150mm rooflight limit is measured off the original roof, meaning the house as built or as it stood on 1 July 1948. On an altered house that is not the slope you can see.
- A dormer is capped at 40 cubic metres of added roof space on a terrace house and 50 anywhere else, and any earlier enlargement has already spent part of it.
- Class B is withdrawn on every category of article 2(3) land, so a dormer needs permission in a National Park or a National Landscape just as in a conservation area.
- Solar sits in Part 14, not Class C: 0.2 metres off a pitched slope, 0.6 metres above a flat roof, and a flat roof on protected land needs prior approval first.
- Since 27 August 2026 a listed house has no permitted development for solar, and listed building consent is needed on top of planning permission.
Rooflights
Class C, and the 0.15 metres almost everybody measures off the wrong plane
A rooflight in the existing slope is normally permitted development under Class C, and the limit that decides it is measured off a roof that may no longer be there. Class C of Schedule 2, Part 1 of the General Permitted Development Order covers any other alteration to the roof of a dwellinghouse.
It must not protrude more than 0.15 metres beyond the plane of the slope of the original roof, measured from the perpendicular with the external surface of the original roof, and no part of it may finish higher than the highest part of the original roof.
"Original" is not "existing", and the Planning Portal blurs it
The Planning Portal's roof page states the rule as 150 millimetres from the plane of the existing roof slope. The Order says original. Different words, different legal meanings, and on plenty of houses they describe different surfaces.
Original has a fixed statutory sense: the building as first built, or as it stood on 1 July 1948 if it went up before then. On an untouched house the two planes are the same. On one where somebody put in a box dormer, turned a hip into a gable or rebuilt a rear slope at a shallower pitch, they are not. Say a rear slope was lifted 200 millimetres in 1994. A rooflight projecting 140 millimetres above what you can measure today projects 340 above the original plane, which is outside Class C. From inside the loft a roofer can often see which one you have, because a rebuilt slope leaves a joint in the timber. The same trap runs through whether a re-roof needs planning permission.
The two Class C provisions people trip over
A window in a side elevation of the roof must be obscure-glazed, and may not open unless the opening part sits more than 1.7 metres above the floor of the room it serves. That is a condition, not a limit, so swapping in an opening light later breaks the permitted development after the fact.
The other is what Class C leaves out: chimneys, flues, soil and vent pipes and solar equipment. Not banned, just not authorised here, so each needs its own answer.
Dormers
Class B, the cubic metres you have already spent, and the land where it does not apply
Anything that enlarges the roof rather than alters it leaves Class C for Class B, which is much the harder to stay inside. It covers a box dormer, a hip turned into a gable, a rear slope rebuilt higher. Four limits do most of the work.
- Volume. The resulting roof space must not exceed the cubic content of the original roof space by more than 40 cubic metres on a terrace house, 50 in any other case.
- Height. No part may end up higher than the highest part of the existing roof, so a dormer cannot poke above the ridge.
- The front. It must not extend beyond the plane of any existing roof slope forming the principal elevation and fronting a highway. That is why box dormers are on the backs of houses.
- Protected land. Class B is not permitted at all where the house is on article 2(3) land.
The volume is cumulative, and end terraces get the smaller number
The allowance runs from the original roof space, not from what is up there now, so an earlier enlargement has already eaten into it. A 1998 rear dormer of 22 cubic metres leaves 28, not 50, and buying after the event changes nothing. The allowance belongs to the building.
The Order also defines a terrace house more widely than most people do: a house in a row of three or more sharing a party wall or an adjoining main wall, and the one at the end of the row too. An end-of-terrace house has 40 cubic metres, not 50, and those ten are often the difference between a usable loft room and an application.
Article 2(3) land is wider than conservation areas
Most pages say a dormer needs permission in a conservation area and stop there. Part 1 of Schedule 1 to the Order defines article 2(3) land as conservation areas, areas of outstanding natural beauty, areas specified under section 41(3) of the Wildlife and Countryside Act 1981, the Broads, National Parks and World Heritage Sites. Class B is withdrawn from all six equally, with no volume small enough to slip under it.
One correction, because it is now the commonest error here. Every area of outstanding natural beauty in England was rebranded a National Landscape on 22 November 2023. The designation itself did not change and the Order still uses the old wording, so a house in a National Landscape is a house in an area of outstanding natural beauty, still article 2(3) land, still with no Class B rights. The rename changed the signage and nothing else. What designation does take away is in re-roofing in a conservation area.
Two other ways to have no rights: flats and buildings containing flats never had Part 1 rights at all, and an article 4 direction can withdraw Class B or Class C on a street carrying no designation.
Solar
Solar is not Class C, and it is not even in the same Part of the Order
Solar has its own class with its own numbers, and quoting the rooflight figures at an installer is how people end up 50 millimetres over. Class C expressly excludes solar equipment. Panels sit in Class A of Part 14, microgeneration equipment.
It was widened in December 2023, and then reorganised by an amending Order in force from 27 August 2026, which split the limits for houses from those for blocks of flats and added rules for walls, balconies and plug-in panels. For a house, the equipment is not permitted development if:
- On a pitched roof, it protrudes more than 0.2 metres beyond the roof slope, measured from the perpendicular with that surface, or sits higher than the highest part of the roof, ignoring the chimney. Five centimetres more than Class C, off a different reference plane.
- On a flat roof, it sits more than 0.6 metres above the highest part of the roof, ignoring the chimney, which is what makes a tilted frame workable.
- On a wall, it protrudes more than 0.2 metres where the wall abuts a highway, or more than 0.4 metres on any other wall.
- On a balcony or roof enclosure, meaning a balustrade, railing or parapet, the same split applies: 0.2 metres beside a highway, 0.4 metres elsewhere.
- In a conservation area or a World Heritage Site, it goes on a wall, balcony or roof enclosure that fronts a highway. The roof slope is not caught.
- It goes on a scheduled monument, or on a listed house or any building in its curtilage.
- It is plug-in solar, meaning panels that connect to the house wiring through a standard plug and socket, and any part of it would go on a wooden wall, balcony or enclosure, or on a timber-clad part of the house.
Two conditions ride with it: the equipment must be sited, so far as practicable, to minimise its effect on the appearance of the building and the amenity of the area, and it must be removed as soon as reasonably practicable once no longer needed.
Flat roofs carry a prior approval trap. On article 2(3) land you must first apply to the authority for a determination as to whether their approval is needed for the appearance of the equipment. Shorter than a planning application, but still an application, and it belongs before the scaffold.
If an installer quoted before 27 August 2026 on something the new limits now catch, article 6 of the amending Order lets development that was permitted before that date, and is not now, go ahead until the end of 26 August 2027.
| What you are adding | The right | The dimension that decides it | What takes it away |
|---|---|---|---|
| Rooflight in the slope | Sch 2, Part 1, Class C | 0.15m off the original roof, never above the original ridge | Flats, an article 4 direction, a condition on the estate's permission |
| Dormer, hip-to-gable, roof raised | Sch 2, Part 1, Class B | 40 cubic metres on a terrace house, 50 otherwise, cumulative | All article 2(3) land, flats, an article 4 direction |
| Solar panels | Sch 2, Part 14, Class A | 0.2m off a pitched slope, 0.6m above a flat roof, 0.2m or 0.4m off a wall | A listed house and its curtilage, scheduled monuments, a highway-facing wall, balcony or roof enclosure in a conservation area |
| Chimney, flue, soil and vent pipe | Excluded from Class C | None applies | Needs its own answer |
Listed houses
Solar on a listed house needs two permissions, not none
Until 27 August 2026, Part 14 Class A removed permitted development only from other buildings in the curtilage of a listed house, not from the house itself. That produced an odd result: you held the planning right on a listed roof and had no lawful way to use it without a separate consent.
The amending Order closed that. Class A now does not apply on a listed dwellinghouse or on any building within its curtilage, so solar on a listed house is a planning application.
It is also a listed building consent application, and that part has not changed. Section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990 says no person shall execute, or cause to be executed, works for the alteration of a listed building in any manner which would affect its character as a building of special architectural or historic interest, unless the works are authorised. Panels bolted to a listed slope are an alteration affecting character in almost every case an officer would look at. The transitional window in article 6 does nothing for that consent, because it sits in a different Act.
This one is criminal, not administrative. Section 9 of the same Act makes it an offence to contravene section 7, and conviction on indictment carries up to two years, a fine, or both. The court must have regard to any financial benefit accruing from the offence when it sets the fine. The one statutory defence is narrow: works urgently necessary for safety, health or preservation of the building, limited to the minimum and notified in writing. Panels do not meet it.
None of this makes solar on a listed building impossible. Authorities grant consent regularly, usually on a concealed slope and often with conditions on frame colour and reversibility. It makes it an application rather than an assumption. That several permission systems run in parallel is the subject of which permission you actually need.
Next steps
What to do, in order
One thing before the list: a yes on planning tells you nothing about building regulations. A dormer cheek and a dormer roof are new thermal elements that have to hit their target U-values, and whether that small flat roof is built warm or cold has a right answer, worked through in warm roof against cold roof and in Part L on a re-roof or loft conversion. Where the insulation ends up decides whether you use the room in February.
- Establish whether the roof you are standing under is the original one. The council's online planning register holds every previous decision on the address.
- Work out what volume is left. Any earlier enlargement comes off the 40 or 50 cubic metres before the drawing starts.
- Check the designations: conservation area, National Park, National Landscape, World Heritage Site, scheduled monument, listed building. Class B goes on the first four.
- On a post-war house, read the conditions on the estate's original permission. Withdrawn rights hide in a decision notice nobody has opened.
- If the house is listed, treat listed building consent as the first job, whatever anybody tells you about permitted development.
- For solar on a flat roof on protected land, apply for the prior approval determination before you book an installer.
- Confirm your own case with your local planning authority. Around here that is BCP Council, Dorset Council or New Forest District Council, except inside the New Forest National Park, which is article 2(3) land and where the National Park Authority decides planning. This page states the general position in England and is not legal advice for your address.
- If the case is arguable rather than clear, apply for a lawful development certificate: a formal ruling that you did not need permission, and what a buyer's solicitor asks for.
Whether the structure and covering will take what you want to put in it is a separate question, answered on the roof rather than on a screen. Thomas comes out, goes up and into the loft, and puts what he found in writing. What we do is on the roofing page, and you can ask for a free written itemised quote without committing to anything.
Questions
Common questions
Do I need planning permission for a rooflight?
Usually not, a rooflight in the existing slope is permitted development under Class C provided it projects no more than 0.15 metres beyond the plane of the original roof and finishes no higher than the highest part of that roof. On a house that has already been altered, the original roof is not the one you can see, so check the planning history first.
Is 150mm measured from the roof I have now?
No, and this is where the Planning Portal and the legislation part company. The Portal says the existing roof slope; the Order says the original roof, meaning the house as built or as it stood on 1 July 1948. On an unaltered house they are the same plane. On an altered one they are not, and the Order is what an enforcement officer applies.
Can I build a dormer in a National Landscape?
Not under permitted development. Class B is withdrawn on all article 2(3) land, which includes areas of outstanding natural beauty. The 2023 rebrand to National Landscapes changed the name and not the statutory designation, so those areas remain article 2(3) land and a dormer there is a planning application.
Do solar panels on a listed house need permission?
Yes, both kinds. Since 27 August 2026 Class A of Part 14 does not apply on a listed dwellinghouse or any building in its curtilage, so solar needs planning permission. Section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990 also requires listed building consent for works affecting the building's character, and doing it without consent is a criminal offence under section 9 carrying up to two years on indictment.
How far can solar panels stick out from the roof?
On a house, no more than 0.2 metres beyond the plane of a pitched roof slope, measured from the perpendicular with that surface, and no higher than the highest part of the roof excluding the chimney. On a flat roof the equipment may sit up to 0.6 metres above the highest part of the roof, and on protected land a flat roof installation needs prior approval first. Since 27 August 2026 panels on a wall may protrude 0.2 metres where the wall abuts a highway and 0.4 metres elsewhere.
Read next
Related advice
The guides below pick up where this one leaves off, and the roofing page covers the work itself and the places we cover, if you would rather have the job looked at.
Who wrote this
Thomas Hannen
Thomas owns Bournemouth Roofing & Building and prices every job himself instead of sending somebody else. The company is Bournemouth Roofing & Building Ltd, number 15471719, registered in England and Wales. If you want to talk something through before you commit to anything, the site visit and the written itemised quote are both free.
Free quote
Want to know whether the roof will take it?
Planning is one question and the structure underneath is another. Thomas comes out himself, gets up on the roof and into the loft, and puts in writing what is there and what the job would involve. The site visit and the written itemised quote are both free.