Most granny flats require planning permission because they create a separate dwelling. Find out exactly when you need to apply — and the rare cases when you don’t.
Yes — in most cases a granny flat needs planning permission because it constitutes a new residential dwelling (C3 use class). The exception is where the building remains genuinely ancillary to the main house and is not self-contained.
A “granny flat” is a common term for a self-contained unit of accommodation, typically in the garden or as part of the main house, intended for family use. In planning law, what matters is not the intended use but the physical characteristics of the building and whether it constitutes a separate dwelling.
If the building has its own entrance, kitchen, bathroom and sleeping area — and could function as an independent home — it is almost certainly a new dwelling in planning terms. This means it falls within the C3 use class and requires a full planning application.
Local planning authorities use a well-established test to decide whether a building constitutes a separate dwelling. The key indicators are:
| Indicator | Separate Dwelling | Ancillary |
|---|---|---|
| Own entrance | Separate external door | Accessed only through main house |
| Kitchen | Full kitchen with cooking facilities | None or kitchenette shared |
| Bathroom | Own bathroom/WC | Shared with main house |
| Can be occupied independently | Yes — does not require use of main house | No — subsidiary to main house |
| Separate utilities | Own meter connections | Shares with main house |
| Postal address | Could have a distinct address | Cannot be separately addressed |
The more of these characteristics are present, the more likely planning permission is required. Councils will look at the building as a whole, not just one factor.
A building in the garden that is used as ancillary accommodation — not as an independent home — may be permitted development under Part 1 Class E of the GPDO 2015. Class E covers buildings within the curtilage of a dwelling house that are incidental to the enjoyment of the dwelling.
Even where a building physically resembles an annexe, it may be treated as a PD outbuilding if:
The concept of “ancillary use” is central to the planning distinction. An outbuilding is ancillary if its use is subsidiary to and in connection with the main dwelling. The planning system does not prevent family members from using an outbuilding as a spare room or occasional sleeping space — but the building must remain subordinate to the main house.
In practice, councils assess ancillary use by looking at:
Even where you believe a granny flat or annexe is permitted development, applying for a Lawful Development Certificate (LDC) from the local planning authority is strongly advisable. An LDC confirms in writing that the development is lawful.
An LDC is important because:
In some areas, local councils have removed Class E permitted development rights through an Article 4 Direction. This is common in conservation areas and in areas where councils are concerned about intensification of use. If an Article 4 Direction applies to your property, you will need planning permission even for ancillary outbuildings that would otherwise be PD.
You can check whether an Article 4 Direction applies by contacting your local planning authority or checking the planning portal on the council’s website.
| Type | Typical Cost Range |
|---|---|
| Purpose-built garden annexe (timber frame) | £50,000 – £100,000 |
| Purpose-built garden annexe (brick/block) | £80,000 – £150,000 |
| Planning application (if required) | £258 householder / £578 full |
| Lawful Development Certificate | £234 |
| Architect / planning consultant fees | £1,500 – £5,000 |
Note: VAT at 20% applies to new-build construction unless specific VAT relief applies (e.g., for disabled adaptations). Converted or extended buildings may attract reduced VAT rates.
Extensions, loft conversions, outbuildings, solar panels — our complete guide covers everything you can build without planning permission.
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