The short answer
- Self-contained means you need permissionA kitchen, a bathroom and a front door of its own makes it separate living accommodation, and that almost always needs a planning application.
- Type and size decide the detailA garage conversion with no outside changes is treated differently to a new detached building, and a caravan has its own rules.
- A householder application costs £548That is the fee in England from April 2026. Most decisions come back within 8 weeks.
- Building regulations apply either wayFire safety, insulation, wiring and drainage need building regulations approval whether or not planning permission was needed.
Rules are for England. Wales, Scotland and Northern Ireland have their own planning systems and figures.
The rule
Why a granny annexe usually needs planning permission
Planning permission is granted by your local council before you build, extend or change how a building is used. For a granny annexe, one question decides almost everything.
If the finished annexe will be self-contained, with its own kitchen, its own bathroom and a front door somebody can use without going through the main house, planning law treats it as a separate home. Separate living accommodation sits outside the smaller category of work a council allows without an application, so you need to apply and wait for a decision before you build. The route below follows the questions a planning officer works through, in order.
- 1
Will it have its own kitchen, bathroom and front door?
YesNeeds full planning permission
Self-contained sleeping accommodation is not "incidental" to the main house, so the permitted development rights that cover garden outbuildings do not apply to it.
No: keep reading, the next question decides it.
- 2
Is it a caravan or park home, kept for the family's own use?
YesUsually does not need planning permission
The Caravan Sites and Control of Development Act 1960 lets a caravan be stationed in a garden for the household's own use without a planning application.
No: keep reading, the next question decides it.
- 3
Is it single storey, under the height and garden-coverage limits, and not on listed or protected land?
YesMay not need planning permission
It can usually be built as permitted development. It still needs building regulations approval, and it has to stay incidental to the house rather than a home in its own right.
NoNeeds full planning permission
Once any of these limits is passed, the council has to look at the plans before you build.
Where the annexe is not self-contained, for example a garage conversion that still shares the house's kitchen and bathroom, smaller projects can go ahead under permitted development: the general permission Parliament has already given for modest work. It comes with limits that catch most annexe projects out, such as staying single storey, keeping to 2.5 metres at the eaves and 4 metres at the ridge, and covering no more than half the garden once other outbuildings are counted in. None of it applies if the house is listed.
Building regulations are a separate approval from planning permission, and they apply to almost any annexe somebody will live in, whether or not planning permission was needed for it. They cover the things that keep a person safe once they have moved in: fire safety, insulation, ventilation, and how the kitchen and bathroom are wired and plumbed. Gov.UK's planning permission guidance is the government's own starting point, and your council's planning department will confirm the position for your specific project before you commit to a design.
By type of annexe
What each type of annexe usually needs
The two things that change the answer are whether the annexe will be self-contained, and how much it alters the outside of the property.
| Usually needs permission? | Why | |
|---|---|---|
| Attached (built onto the house) | Almost always | It alters the existing structure, and is usually self-contained. |
| Detached (a new building in the garden) | Almost always | A new self-contained building is treated as a separate home. |
| Conversion (garage, loft or outbuilding) | Depends | No permission if the internal work does not change the outside and it stays non-self-contained; permission is needed once it gets its own kitchen and bathroom, or the outside changes. |
| Mobile or caravan-based | Often not | Covered by the Caravan Sites and Control of Development Act 1960 if it is kept for the family's own use, though size and how permanent it looks can still bring it back into the planning system. |
Attached (built onto the house)
- Usually needs permission?
- Almost always
- Why
- It alters the existing structure, and is usually self-contained.
Detached (a new building in the garden)
- Usually needs permission?
- Almost always
- Why
- A new self-contained building is treated as a separate home.
Conversion (garage, loft or outbuilding)
- Usually needs permission?
- Depends
- Why
- No permission if the internal work does not change the outside and it stays non-self-contained; permission is needed once it gets its own kitchen and bathroom, or the outside changes.
Mobile or caravan-based
- Usually needs permission?
- Often not
- Why
- Covered by the Caravan Sites and Control of Development Act 1960 if it is kept for the family's own use, though size and how permanent it looks can still bring it back into the planning system.
Every row assumes the property is not listed and not in a conservation area, where the rules are tighter.
If you are weighing up which type to build, how much it would cost to build a granny annexe sets typical build costs for each of these against each other, and do granny annexes add value covers what a finished annexe is worth once it is built. A self-contained annexe can also be rated separately for council tax once it exists, which is worth knowing before you choose which type to build.
Applying
How to apply, what it costs, and what happens if you are refused
If the annexe will be self-contained, plan for a formal application rather than hoping it slips through as permitted development.
- 1
Ask the council before you finalise the design
Before you applyMost councils offer pre-application advice, and you can apply for a Certificate of Lawful Development if you want written confirmation that a smaller project does not need permission. Both are worth having if a parent is moving in soon and you cannot afford a delay. - 2
Submit a householder planning application
Fee and timescaleThe fee in England is £548 from April 2026. Most applications are decided within 8 weeks, or 13 weeks for larger or more complex proposals. - 3
Apply for building regulations approval separately
Before building startsThis runs alongside or after planning permission and cannot be skipped for a habitable annexe, even one that did not need planning permission. - 4
If you are refused, amend or appeal
If it goes wrongMany councils will discuss changes that would make a refused scheme acceptable, and resubmitting a revised application is often free within a set period. You can also appeal to the Planning Inspectorate, free of charge, within 12 weeks of a householder refusal.
Questions
Questions families ask about annexe planning permission
In most cases, yes. A granny annexe with its own kitchen, bathroom and front door counts as self-contained living accommodation, and that almost always needs a planning application to your local council. Only smaller, non-self-contained conversions, and some caravans kept for the family's own use, can go ahead without one.
Sometimes. A conversion of an existing garage or outbuilding that does not add a separate kitchen and bathroom, and does not change the outside of the building, can often go ahead as permitted development. A caravan or park home kept in the garden for your own family's use can also avoid the need for permission under the Caravan Sites and Control of Development Act 1960. Building regulations approval is still needed in both cases.
The householder planning application fee in England is £548 from 1 April 2026. It is the same fee whether the application is approved or refused, and it does not include the cost of drawings, a planning consultant, or building regulations approval.
Most householder applications are decided within 8 weeks. Larger or more complicated proposals, including some annexes, can take up to 13 weeks. Add time before that for drawing up plans and, if you use one, getting pre-application advice from the council.
You can ask the council whether a revised scheme would be acceptable and resubmit, which many councils allow free of charge within a set period. You can also appeal to the Planning Inspectorate, which is free, within 12 weeks of a householder refusal. Appeals typically take several months to decide, so most families try an amended application first.
Yes. Building regulations are a separate approval from planning permission and cover fire safety, insulation, ventilation, and the electrics and plumbing for a kitchen and bathroom. They apply to almost any annexe someone will live in, regardless of whether planning permission was needed for the building itself. If the annexe is for a parent who will need help once they move in, a carer found through hourly care can visit the annexe in the same way as any other home.