Can I convert a garage to a granny flat without planning permission?

Converting a garage to an ancillary annexe (not self-contained) may be Permitted Development. However, creating a self-contained dwelling with its own kitchen, bathroom and separate entrance within the converted garage almost always requires Full Planning Permission, as this constitutes a separate planning unit - a new dwelling on the land.

What is the difference between an annexe and a separate dwelling for planning purposes?

An annexe is accommodation that is subordinate and ancillary to the main dwelling - it is used by a family member, shares some services or access with the main house, and is not self-contained in a way that would allow it to function as an entirely independent household. A separate dwelling is self-contained with its own kitchen, bathroom and means of access and is capable of independent occupation. Planning authorities assess this based on the physical characteristics and how the accommodation would be used.

Do I Need Planning Permission for a Granny Flat or Annexe?

Q: Do I need planning permission for a granny flat?

It depends on whether the granny flat is attached to or detached from the main house, and critically whether it is self-contained. An annexe integrated into the main dwelling, sharing facilities, and without its own kitchen may be Permitted Development as an extension. A self-contained unit with its own kitchen, bathroom and separate entrance - whether attached or detached - is likely to be treated as a separate dwelling and will almost always require Full Planning Permission.

Annexe or Separate Dwelling - the Critical Distinction

The planning status of a granny flat or annexe hinges on one question: is the accommodation ancillary to the main house, or is it a self-contained separate dwelling? This distinction determines whether you need planning permission and has significant implications for council tax, permitted development rights and mortgage conditions.

An ancillary annexe is subordinate to the main house, used by a family member, and not capable of fully independent occupation. A separate dwelling has its own kitchen, bathroom and entrance and can function independently. Planning permission is almost always needed for the latter.

Single storey side extension to a detached house in England being used as a connected granny annexe with its own entrance — An attached annexe connected to the main house - may be Permitted Development if it meets the extension rules and is not fully self-contained.

Attached Annexe - When PD May Apply

An annexe built as part of an extension to the main house may be Permitted Development if:

The physical extension meets all the PD extension rules (size, height, position)
The annexe does not have its own separate council tax banding
There is internal access between the annexe and the main house
The annexe does not function as a wholly independent dwelling

When Full Planning Permission Is Required

The annexe is a detached building (outbuilding used as living accommodation requires PP)
The accommodation is self-contained with its own kitchen and bathroom
There is no internal connection to the main house
The annexe will have a separate address or council tax banding
The extension would not meet standard PD extension limits even without the self-contained issue
Listed building or conservation area applies

Detached Granny Flat

A detached building used as a granny flat is assessed as an outbuilding. Under outbuilding PD rules, an outbuilding must not be used as a dwelling - it must remain ancillary to the main house. A detached outbuilding with a full kitchen, bathroom and bedroom is almost certainly being used as a separate dwelling and will require planning permission. Some councils have very specific policies against detached self-contained units in residential gardens.

Council Tax: A self-contained annexe - even if currently used by a family member - may be liable for a separate council tax bill. Some councils offer a discount for annexes used by family members, but this varies. Check with your local authority before building.

Conversion of an Existing Outbuilding

Converting an existing garage or outbuilding to a granny flat falls into the same category as new-build. Interior works to a garage (no external changes) may be PD if the result is ancillary accommodation. Adding a kitchen to create a self-contained unit within the converted garage will normally require planning permission.

Planning Application for an Annexe

If you do need to apply for planning permission, local authorities generally consider:

Scale relative to the main house and plot
Impact on neighbouring properties - overlooking, loss of light
Whether the unit would function as a separate dwelling (intensification of use)
Whether there will be adequate parking for both households

A planning condition may be imposed restricting occupation to a dependent relative of the occupier of the main house, preventing the annexe from being sold or let separately.

Building Regulations

Whether or not planning permission is needed, an annexe with a bedroom, kitchen and bathroom will require Building Regulations approval. The works will be assessed under Part M (accessibility), Part L (energy efficiency) and Part P (electrical safety), among others. A full plans application is recommended for any annexe project.

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Granny Flat / Annexe:Planning Permission Rules