Probably not, if you live in a house rather than a flat, you are building within the size limits below, and your home is not listed or in a conservation area. Most loft conversions, single storey rear extensions and garden rooms in England are permitted development, which means they are already allowed and need no planning application at all.
The rules that decide this sit in the Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1. This guide works through them project by project, tells you plainly where the cut-off is, and attaches the actual costs, because knowing you need permission is only half of a decision.
Key Takeaways
- Permitted development rights apply to houses only. Flats and maisonettes have none, so almost any external alteration to a flat needs a planning application.
- Loft conversions are permitted development under 40m³ of added volume for a terraced house, 50m³ for a semi-detached or detached house, with nothing projecting beyond the front roof slope.
- Single storey rear extensions are permitted development to 3m deep for terraced and semi-detached houses, 4m for detached, rising to 6m and 8m through the larger home extension prior approval route.
- Conservation areas, listed buildings and Article 4 directions remove or cut back these rights. Check before you design, not after.
- Building regulations are a separate approval. Permitted development exempts nothing from building control.
- A householder planning application costs £548 in council fee in England from 1 April 2026. A lawful development certificate, which proves you did not need permission, costs half the equivalent planning fee.
The first question: house or flat?
If you live in a flat or a maisonette, you have no permitted development rights and the rest of this guide's limits do not apply to you. Schedule 2, Part 1 of the 2015 Order grants rights to a "dwellinghouse", and the Order expressly excludes buildings containing one or more flats and any flat within such a building.
This catches people out constantly. A ground floor flat with its own front door, its own garden and its own council tax band is still a flat. Adding a rear extension, converting the loft above you, or in many cases replacing the windows will need a planning application. Leasehold consent from the freeholder is a separate matter again, and getting one does not substitute for the other.
Converted houses are the grey area worth checking. If the building was split into flats at some point, the permitted development rights attached to the original house are gone, even if you now own the whole building and occupy it as a single home. Rights are restored only when the lawful planning use returns to a single dwellinghouse.
What "permitted development" actually means
Permitted development is a national grant of planning permission, given in advance by the Order itself. Nobody assesses your scheme, nobody consults your neighbours and nobody can refuse it, provided you stay inside every condition and limitation attached to the relevant Class.
Two things follow from that. First, the limits are absolute rather than negotiable. A rear extension at 3.1m on a semi-detached house is not "nearly" permitted development, it is a planning application. Second, you cannot trade one allowance against another. Being well under the height limit does not buy you extra depth.
Where the rights are taken away
Three mechanisms remove or restrict what follows:
- Conservation areas and other designated land, which also covers National Parks, the Broads, Areas of Outstanding Natural Beauty and World Heritage Sites. Side extensions, rear extensions of more than one storey, cladding and roof alterations including dormers all lose their rights here.
- Listed buildings, where the works additionally need listed building consent. That is a separate consent from planning permission, it applies internally as well as externally, and carrying out works without it is a criminal offence rather than a civil planning breach.
- Article 4 directions, where a council has formally withdrawn a specific permitted development right across a defined area. These are common across inner London and in Victorian suburbs everywhere, and they are frequently aimed at the exact things owners want to do: front windows, roof alterations, front boundary walls, hardstanding and small HMO conversions.
Your council's planning policy map shows conservation area boundaries and Article 4 areas. Check it first, because an Article 4 direction changes the answer for every section that follows.
Quick answer table
| Project | Usually permitted development? | The limit that decides it |
|---|---|---|
| Loft conversion, rear dormer | Yes, on a house | Under 40m³ terraced, 50m³ semi or detached; nothing forward of the front roof slope |
| Loft conversion in a conservation area | No | Roof alterations lose PD rights on designated land |
| Single storey rear extension | Yes, on a house | 3m terraced or semi, 4m detached, max 4m high |
| Rear extension, 6m or 8m | Prior approval, not a full application | Larger home extension route with neighbour consultation |
| Garden room or outbuilding | Yes, on a house | Single storey, 2.5m high within 2m of a boundary, no sleeping space |
| Like-for-like window replacement | Yes, on a house outside a designated area | Materials of similar appearance |
| New bay window | No | Treated as an extension, not a replacement |
| Anything on a flat | No | Flats have no permitted development rights |
| Anything on a listed building | No | Planning and listed building consent both engaged |
| House to small HMO, up to six people | Usually, outside Article 4 areas | C3 to C4 change of use |
| HMO for seven or more people | No | Sui generis, always needs permission |
Loft conversions
A loft conversion on a house is permitted development if the added roof volume stays under 40m³ for a terraced house or 50m³ for a semi-detached or detached house. Those figures are cumulative across the life of the building, so an earlier dormer built by a previous owner eats into your allowance.
Four conditions matter as much as the volume:
- Nothing may extend beyond the plane of the existing front roof slope. A rear dormer is fine, a front dormer is a planning application.
- Materials must be similar in appearance to the existing house.
- Side-facing windows must be obscure-glazed, and non-opening unless the opening part is more than 1.7m above the floor of the room.
- Roof alterations lose permitted development rights entirely on designated land, which is why conservation area lofts nearly always need an application.
The 40m³ limit is the one that bites in terraced streets. A full width rear dormer across a standard London terrace can consume most of it before you have added the obligatory dormer cheeks, so the volume calculation is a design input rather than a compliance check at the end.
Single storey rear extensions
A single storey rear extension is permitted development to 3m deep on a terraced or semi-detached house and 4m on a detached house, with a maximum height of 4m. Depth is measured from the original rear wall of the house as it stood on 1 July 1948 or as first built, not from whatever is there now, so an existing extension counts against you.
The larger home extension route
Beyond those depths, the Order provides a second, longer right: 6m for terraced and semi-detached houses and 8m for detached houses, subject to prior approval. This is not a planning application. You notify the council, the council notifies the adjoining owners, and if none of them objects within the consultation period the extension proceeds as permitted development.
The practical distinction is what the council is allowed to consider. Under prior approval, it can only assess the impact on the amenity of adjoining properties, and only if a neighbour objects. It cannot refuse on design, on materials or on planning policy grounds, which it can under a full householder application. One objecting neighbour does not defeat the scheme either, it simply moves the decision to the officer on amenity grounds alone.
The 4m height limit applies throughout, and the extension must be at the rear rather than the side.
Outbuildings and garden rooms
A garden room is permitted development if it is single storey, no more than 2.5m high where any part sits within 2m of a boundary, covers no more than half the curtilage of the original house together with other outbuildings, and sits no further forward than the principal elevation.
The condition people breach without realising is the last one: no sleeping accommodation. An outbuilding is permitted development as an incidental building, a home office, a gym, a studio or storage. The moment it contains a bedroom it becomes a separate dwelling or an extension of the existing one, and it needs planning permission. Councils enforce this, and it surfaces reliably at sale when a buyer's solicitor asks what the annexe is.
"Half the curtilage" means half the garden, counting every outbuilding that is already there, including sheds and the garage.
Windows and doors
Replacing windows and doors like for like is normally permitted development on a house outside a designated area, provided the replacements are of a similar appearance to the originals. Changing a timber sash for a plastic casement in a conservation area, or anywhere an Article 4 direction covers fenestration, is not.
New openings follow different rules from replacements. A new bay window projects and is treated as an extension rather than a replacement, so it does not benefit from the replacement right. New upper floor side windows must be obscure-glazed and non-opening below 1.7m, the same condition that applies to loft windows.
Changing a house into an HMO
Changing a house into a small HMO for up to six people, use class C3 to C4, is permitted development in most of England. It is also one of the most heavily restricted rights in the country, because many London boroughs and university towns have Article 4 directions removing it. In those areas a planning application is required for the change of use.
An HMO for seven or more people falls outside the use classes altogether. It is sui generis, and it always needs planning permission regardless of where it is. Licensing is separate again: mandatory HMO licensing and any additional or selective licensing scheme your council runs apply whether or not planning permission was needed.
Building regulations are a separate approval
Permitted development exempts nothing from building regulations. These are two different legal regimes with different authorities, different applications and different fees, and satisfying one says nothing about the other.
A loft conversion is the clearest example. It may be permitted development on volume, and it will still need to satisfy Part B for means of escape, typically a protected stair and fire doors, and Part A for structure, because the existing ceiling joists were never designed to carry a floor. A single storey rear extension engages Part A, Part L for thermal performance and Part K for stairs and guarding.
Work carried out without building control sign-off shows up at sale as a missing completion certificate, and retrospective regularisation costs more than doing it properly. Budget for building control from the start.
What each route costs
| Route | Council fee | Typical timescale |
|---|---|---|
| Permitted development, no application | None | None, you can start |
| Lawful development certificate (proposed) | Half the equivalent planning fee, £274 on a householder scheme | 8 weeks |
| Householder planning application | £548 | 8 weeks |
| Full application on a dwellinghouse | £610 | 13 weeks |
Council fees are England, from the 1 April 2026 indexation. They are paid to your local planning authority, not to a designer or an agent, and they are separate from any drawing fee. Determination targets are statutory: 8 weeks for householder applications and 13 weeks for a full application, subject to any extension of time you agree with the case officer.
Proving you did not need permission
Permitted development gives you no paperwork. That is fine until you sell, remortgage or a neighbour complains, at which point you need to evidence that the work was lawful, and photographs of a finished dormer do not establish what its volume was.
A lawful development certificate is the formal answer. You apply to the council with drawings, the council assesses whether the scheme falls within the Order, and the certificate it issues is conclusive proof for the property's lifetime. The application fee is half the equivalent planning fee, £274 on a householder scheme, and the determination target is 8 weeks. Fixed Fee Plans charges from £950 for the drawings and submission.
It is not compulsory. It is worth having when the scheme sits anywhere near a limit, when you are likely to sell within a few years, or when a neighbour has already expressed a view about your dormer.
Frequently asked questions
Does permitted development apply in Scotland, Wales or Northern Ireland?
No. The Order in this guide is the England version. Scotland, Wales and Northern Ireland each have their own permitted development legislation with different thresholds, so none of the volumes or depths above transfer.
My neighbour built a bigger extension than the limit allows. Can I?
Not automatically. They may have obtained planning permission, used the larger home extension prior approval route, or built in breach. None of those makes your identical scheme permitted development, and the limits apply to each house on its own facts.
Do I need permission for a driveway or hardstanding?
Laying a hard surface at the front of a house is permitted development if the material is porous or if run-off drains to a permeable area within the property. Non-porous surfacing above 5m² that drains to the highway needs planning permission. Article 4 directions in conservation areas frequently remove this right.
Can I start work while a lawful development certificate is pending?
Yes, because the certificate confirms an existing right rather than granting a new one. The risk is that the council disagrees with your interpretation after you have built, so on a marginal scheme it is worth waiting for the decision.
How long do permitted development rights last?
They are not time limited in the way a planning permission is, but they can be withdrawn. A new Article 4 direction, a conservation area designation or a condition attached to an earlier permission on your property can all remove rights you had last year. New build estates commonly carry conditions removing permitted development rights entirely, so check your title and any existing permission.
What to do next
Work through it in order. Confirm you own a house rather than a flat. Check your council's policy map for conservation area status and Article 4 directions. Measure your scheme against the limit in the relevant section above, from the original wall or roof rather than the current one. If it fits, you can build, and the only question left is whether to certify it.
If it does not fit, you have a choice worth pricing before you make it: redesign to the limit and avoid an application altogether, or apply and get the scheme you actually want. The gap between a £274 certificate and a £548 application is small enough that design, not fees, should decide it.
Sources
- Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1: https://www.legislation.gov.uk/uksi/2015/596/schedule/2/part/1
- Town and Country Planning (General Permitted Development) (England) Order 2015, full text and amendments: https://www.legislation.gov.uk/uksi/2015/596/contents
- Permitted development rights for householders: technical guidance, Ministry of Housing, Communities and Local Government: https://www.gov.uk/guidance/permitted-development-rights-for-householders-technical-guidance
- Planning practice guidance, when is permission required: https://www.gov.uk/guidance/when-is-permission-required
- Planning practice guidance, lawful development certificates: https://www.gov.uk/guidance/lawful-development-certificates
- Town and Country Planning Act 1990, section 192 (certificate of lawfulness of proposed use or development): https://www.legislation.gov.uk/ukpga/1990/8/section/192
- Planning Portal, common projects, extensions: https://www.planningportal.co.uk/permission/common-projects/extensions
- Planning Portal, common projects, outbuildings: https://www.planningportal.co.uk/permission/common-projects/outbuildings
- Approved Documents (building regulations), including Part A structure and Part B fire safety: https://www.gov.uk/government/collections/approved-documents
- Council application fees: Town and Country Planning (Fees for Applications) Regulations, annual indexation from 1 April 2026, as recorded in the site fee schedule