Loft conversion: do you need planning permission?
When a loft conversion needs planning permission in England, the 40 and 50 cubic metre limits for dormers, what a certificate costs, and the rules in Wales, Scotland and Northern Ireland.
Most loft conversions in England need no planning application, because a rear dormer, a hip to gable or a rooflight conversion usually fits the permitted development allowances for a house. A mansard, a front dormer, a flat, a listed house or a conservation area changes the answer. We set out the limits, which conversions need permission, what the paperwork costs, and how Wales, Scotland and Northern Ireland differ.
Do you need planning permission for a loft conversion?
In England, usually not. A loft conversion is permitted development when it stays within the limits of Class B of the permitted development order. It needs a householder planning application when the design breaks one of those limits, or when the house has no permitted development rights to begin with.
Of the four types of loft conversion, a rooflight conversion, a dormer and a hip to gable usually fit the rules, and a mansard needs an application. The table covers the common designs on a house in England with its rights intact.
| Conversion | Planning application? | The rule that decides it |
|---|---|---|
| Rooflight (velux) | Usually not | Rooflights projecting no more than 0.15 m from the slope are permitted development |
| Rear dormer | Usually not | Fits if it adds no more than 40 m³ on a terrace or 50 m³ on other houses |
| Hip to gable | Usually not | Same volume limit; the 20 cm set-back from the eaves does not apply |
| Front dormer facing a road | Yes | Nothing may project beyond the front roof slope where it faces a highway |
| Mansard | Yes | Rebuilds the roof slope and changes the shape of the roof |
| Piggyback or raised ridge | Yes | Nothing may rise above the highest part of the existing roof |
| Any loft in a flat or maisonette | Yes | Flats have no householder permitted development rights |
| Any roof extension in a conservation area | Yes | The loft rules do not apply on designated land |
Permitted development rules for a loft conversion in England
A loft conversion in England is permitted development only if it meets every one of the Class B conditions for loft conversions in the Town and Country Planning (General Permitted Development) (England) Order 2015:
- Volume: no more than 40 cubic metres of added roof space on a terraced house, or 50 cubic metres on a semi-detached or detached house, counting any earlier roof enlargement.
- Height: nothing higher than the highest part of the existing roof.
- Front slope: nothing beyond the plane of the roof slope on the principal elevation, where it faces a highway.
- Eaves: the original eaves kept, the new work set back at least 20 centimetres from them as far as practicable, and nothing overhanging the outside face of the wall.
- Side windows: obscure-glazed, with any opening part at least 1.7 metres above the floor.
- No balconies: no verandas, balconies or raised platforms, and no new or altered chimney, flue or soil and vent pipe.
- Materials: similar in appearance to the existing house.
The house has to qualify too. The loft rules do not apply to a flat or a building containing flats, to a house that has already had storeys added under permitted development, to a house created by converting a non-residential building, or to one on designated land such as a conservation area.
How the 40 and 50 cubic metre limits are measured
The limit is the volume the conversion adds to the roof, and it counts every earlier roof enlargement since the original house. The original house is the house as it stood on 1 July 1948, or as built if it is newer, so a dormer a previous owner added uses part of your allowance.
A rooflight conversion adds no volume, because the roof keeps its shape. A rear dormer adds the box it builds out from the slope and a hip to gable adds the new gable end, so the two together on a semi-detached house share one 50 cubic metre allowance.
Dormer, velux and hip-to-gable conversions: which need permission
Dormer loft conversions
A rear dormer usually needs no planning application in England if it stays within the volume limit, sits 20 centimetres back from the eaves as far as practicable, and uses materials that match the house.
A dormer on the front slope, where it faces a road, always needs an application. A side dormer can be permitted development, but its windows must be obscure-glazed, with any opening part at least 1.7 metres above the floor.
Velux and rooflight conversions
Rooflights in a velux conversion come under Class C rather than Class B. They are permitted development if they project no more than 0.15 metres from the roof slope and sit no higher than the highest part of the original roof.
Rooflights in a side slope must be obscure-glazed. Because they add no volume and lie almost flush with the slope, rooflights can go on the front of the house where a dormer cannot.
Hip-to-gable conversions
A hip to gable rebuilds the sloping side of a hipped roof as a vertical gable wall, and it falls under Class B like a dormer. The 20 centimetre set-back from the eaves does not apply to it, but the new gable still counts toward the volume limit.
Mansard conversions and raising the roof
A mansard conversion rebuilds the rear slope almost vertical under a flat top. That changes the shape of the roof, so it needs a householder planning application. So does a piggyback, which lifts the whole roof, and any design that raises the ridge above the existing roof.
When a loft conversion needs planning permission
In England a loft needs a householder application when the design breaks a limit, or when the house has lost its rights. These are the common triggers:
- A flat or maisonette. Flats have no householder permitted development rights, so any loft conversion in one needs an application.
- Designated land. In a conservation area, a National Park, a National Landscape (area of outstanding natural beauty), the Broads or a World Heritage Site, the loft rules do not apply at all.
- A listed building. A loft conversion needs planning permission and listed building consent.
- Rights removed. An Article 4 direction, or a condition on the house's original planning permission, can take the rights away. Check in particular on a newer estate.
- A design over the limits. More than 40 or 50 cubic metres, anything beyond the front slope facing a road, a raised ridge, or a balcony or roof terrace.
Lawful development certificates and planning fees
Nobody has to approve a permitted development loft, and there is no application to make. A lawful development certificate is the optional step: the council checks the drawings against the limits and confirms in writing that the conversion is lawful. It is also the proof a buyer's solicitor asks for when you sell.
In England a certificate for proposed work costs £274, half the £548 householder planning fee that applies from 1 April 2026. Planning fees rise each April in line with inflation.
A householder application usually takes about 8 weeks from validation, so a loft that needs one adds about 2 months before the builder can start. The fees are small beside what a loft conversion costs: a dormer runs £42,000 to £72,000 including VAT, and a mansard £66,000 or more.
Building regulations approval for a loft conversion
Planning and building regulations are separate systems. Every loft conversion in England needs building regulations approval, including one built under permitted development, from the council's building control team or a registered building control approver.
Building control checks the structure under Part A, fire safety and escape under Part B, the staircase under Part K and insulation under Part L. A full plans application gets a decision within 5 weeks, or 2 months if you agree to more time. A building notice, meant for smaller projects, lets work start 2 days after it goes in but gives no approval of the plans in advance.
Over the stairs, Approved Document K asks for 2 metres of headroom, relaxed for a loft to 1.9 metres at the centre and 1.8 metres at the side. When the finished work complies, the council issues a completion certificate, usually within 8 weeks, and a buyer's solicitor will ask to see it.
Party wall notices for a loft conversion
In England and Wales, a loft on a terraced or semi-detached house usually means structural work to the party wall. Cutting into it to take the bearing of a beam is work the Party Wall Act 1996 covers, and it needs a party structure notice served on the neighbour at least 2 months before work starts.
The neighbour has 14 days to reply. Written consent means no surveyor's fee. A dissent, or no reply at all, starts the dispute process, and a party wall award for a loft costs £1,200 to £3,000 per agreement, with a mid-terrace house needing one for each side. The Act does not apply in Scotland or Northern Ireland.
What happens if you convert a loft without planning permission
If a loft needed planning permission and was built without it, the council can serve an enforcement notice ordering you to undo all the changes. It is illegal to ignore an enforcement notice, but you can appeal against it, and an owner can apply for permission after the work is done.
Time limits apply. Under section 171B of the Town and Country Planning Act 1990, a council in England cannot take enforcement action against building work once 10 years have passed since it was substantially completed. The 10 year limit took effect on 25 April 2024, with transitional rules for older work, and in Wales the limit is 4 years.
The time limit covers planning only. Work done without building regulations approval can be put right through regularisation, which is retrospective approval from the council for work carried out after 11 November 1985. Without it, the council can make you pay to fix faulty work, and there is no certificate to give a buyer.
Loft conversion planning rules in Wales, Scotland and Northern Ireland
Everything above is England's law. Wales, Scotland and Northern Ireland write their own permitted development rules for roofs, and only Wales uses a volume allowance like England's.
| Nation | Size limit | Road-facing slope | Other main limits | Conservation area |
|---|---|---|---|---|
| England | 40 m³ on a terrace, 50 m³ on other houses | Nothing beyond the front slope where it faces a highway | 20 cm set-back from the eaves; side windows obscure-glazed | No permitted development |
| Wales | Under 40 m³ on a terrace, under 50 m³ on other houses | Nothing beyond the slope on the principal elevation | 20 cm from the eaves except hip to gable; side windows within 10.5 m of a boundary obscure or non-opening | No permitted development |
| Scotland | Dormer no wider than half the roof plane at the eaves | Not on a principal or side roof plane that fronts a road | At least 10 m from the boundary the roof plane faces; 0.3 m from every edge of the roof plane | No permitted development |
| Northern Ireland | No volume limit | No more than 15 cm beyond a road-facing principal or side slope | 0.5 m from the ridge, eaves, party wall and verge; side windows within 15 m of a neighbour's boundary obscure-glazed | No permitted development |
Wales
Wales has run its own planning system since 2016, and its loft conversion rules keep England's volume limits, the ban on building beyond the front slope and the 20 centimetre set-back from the eaves.
The differences are in the detail. uPVC is not acceptable on the dormer other than possibly for the windows, and a Juliet balcony is allowed only with no platform and no more than 300 millimetres of projection. Roof extensions are not permitted development in conservation areas, National Parks, areas of outstanding natural beauty or World Heritage Sites.
Scotland
Scotland's rules are in planning circular 1/2024, and they control a dormer by where it sits rather than by its volume. Besides the limits in the table, a dormer cannot make the house taller, and none of the rights apply in a conservation area or to a flat.
Rooflights and other small roof alterations that project no more than 1 metre come under a separate class, again not in a conservation area. A building warrant, Scotland's version of building regulations approval, may also be required from the council.
Northern Ireland
Northern Ireland's rules are Class B of the Planning (General Permitted Development) Order (Northern Ireland) 2015. It sets no cubic metre allowance, and nothing may rise above the highest part of the existing roof.
Balconies and decks are not permitted, and side windows must be fixed shut below 1.7 metres as well as obscure-glazed. A house in a conservation area gets no permitted development for roof work, and neither does one within the grounds of a listed building unless listed building consent has already been granted. Northern Ireland runs its own building control as well.
Common questions
What happens if you do a loft conversion without planning permission?
If the loft needed planning permission, the council can serve an enforcement notice ordering you to undo all the changes. Ignoring the notice is illegal, though you can appeal against it. In England enforcement action is barred once 10 years have passed since the work was substantially completed, and in Wales after 4 years.
What is the 10 year rule for loft conversion?
The 10 year rule stops a council in England taking planning enforcement action against building work done without permission once 10 years have passed since it was substantially completed. It comes from section 171B of the Town and Country Planning Act 1990, in force since 25 April 2024. It does not cover building regulations, so a missing completion certificate still surfaces at a sale.
Can I convert my loft myself?
You can convert a loft yourself, but the approvals are the same as for a builder: building regulations approval every time, and planning permission where the design breaks the permitted development limits. As the owner you are ultimately responsible for complying with the building regulations. Every conversion also needs a structural engineer's calculations for the new floor and steels.
Do I need to tell the council about a loft conversion?
You need to tell building control about every loft conversion, through the council or a registered building control approver, because building regulations approval is always required. A permitted development loft needs no planning application, although a £274 lawful development certificate confirms it is lawful. A loft that breaks the limits needs a £548 householder application in England.
Do you need planning permission for a dormer loft conversion?
A rear dormer usually needs no planning permission in England if it adds no more than 40 cubic metres on a terrace or 50 on other houses. A dormer on the front slope facing a road always needs an application, as does any dormer on a flat, a listed building or a house in a conservation area.
Do you need planning permission for velux windows in a loft?
Velux and other rooflights need no planning permission in England if they project no more than 0.15 metres from the roof slope and sit no higher than the highest part of the roof. Rooflights in a side slope must be obscure-glazed. A flat, a listed building or an Article 4 direction can change that.
Do you need planning permission for a loft conversion in a bungalow?
A bungalow follows the same rules as any other house, so a loft conversion needs no planning application in England if it adds no more than 50 cubic metres on a detached or semi-detached bungalow, or 40 on a terraced one. Raising the roof to gain head height needs an application, because nothing may rise above the highest part of the existing roof.
Do you need planning permission for a loft conversion in Scotland?
A dormer in Scotland needs no planning permission if it avoids a roof plane fronting a road, stands at least 10 metres from the boundary its roof plane faces and covers no more than half the roof's width at the eaves. Flats and conservation areas get no permitted development for it, and a building warrant may still be needed.
Do you need planning permission for a loft conversion in Northern Ireland?
A loft conversion in Northern Ireland can be permitted development if nothing rises above the roof, nothing stands more than 15 centimetres beyond a road-facing slope, and the work stays 0.5 metres from the ridge, eaves, party walls and verge. Conservation areas get no permitted development for roof work.
Can my neighbour stop my loft conversion?
A neighbour cannot stop a loft conversion that is permitted development, because there is no planning application to object to. In England and Wales a neighbour who dissents from a party wall notice cannot block the work either. The party wall award sets how and when the work is done, and who pays for any damage.