Granny annexes: the planning routes a buyer checks
A granny annexe in a garden in England is judged by how it will be used and who will live in it, not by whether it arrives as a timber kit, a brick extension or a twin-unit mobile home. This page sets out the routes a buyer in England checks before ordering: an ancillary annexe application, Class E permitted development, the caravan definition, the lawful development certificate, and the building regulations and council tax questions that follow.
Nothing here is legal advice and nothing here says that a particular building needs no permission. The rules described are those for England; Wales, Scotland and Northern Ireland run their own planning systems with different orders and thresholds, and the Republic of Ireland has a separate system this page does not describe. Eurodita manufactures the timber kit shown on the granny annexes hub; the planning route stays with the buyer, the dealer or the project team.
At a glance
Does a granny annexe need planning permission?
For many projects, yes. Where a buyer believes permission is not required, a lawful development certificate is the formal way to ask the council to confirm that position. GOV.UK states that you will probably need planning permission if you want to build something new or change the use of a building, and a bedroom, kitchen and bathroom in the garden will usually raise both new-building and use questions. Rother District Council puts the local position plainly: annexes will generally require planning permission. A buyer who assumes otherwise usually meets the problem when the main house is sold and the solicitor asks for the paperwork.
The real question is which of three routes applies: an application for an ancillary annexe conditioned to the main house; Class E permitted development, narrower than most guides suggest; or the mobile home route, where a structure meeting the legal definition of a caravan is used in association with the house. Each faces the same use test.
Ancillary annexe or separate dwelling: why the use test matters more than the building
Planning officers look past the building to the relationship between the annexe and the main house. Cornwall Council’s annexe guidance asks that an annexe has a functional link with and is ancillary to the principal dwelling, so that occupants rely on facilities in the main house, is in the same ownership and curtilage, shares the vehicular access, and has no subdivided garden. Rother District Council frames it from the other side: an annexe occupied independently, with no relationship to the main dwellinghouse, requires permission as a new dwelling.
This is why use matters more than the wall system or the floor plan. A one-bedroom cabin with its own kitchen is capable of independent use, but capability is not use. Councils weigh separate meters, a separate postal address or a fenced-off garden as signs of a separate dwelling. Where permission is granted, a council may use a condition to the effect that the annexe shall only be used as ancillary accommodation and occupied only by members of the family or non-paying guests of the occupiers of the dwelling.
Permitted development outbuildings and why an annexe usually is not one
Class E of Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 permits, within the curtilage of a dwellinghouse, any building required for a purpose incidental to the enjoyment of the dwellinghouse as such, giving poultry, bees and pet animals as examples. Garden offices, studios and stores can sit inside it where the use is incidental and the Class E limits and conditions are met. Self-contained living accommodation for a resident relative is normally treated as residential use rather than merely incidental outbuilding use, and the Planning Portal states that the outbuilding rules do not cover use as separate self-contained living accommodation.
The physical limits still apply to any garden building. Under Class E the building must not stand forward of the principal elevation, must be single storey with eaves no higher than 2.5 m, must not exceed 4 m overall with a dual-pitched roof or 3 m with any other roof, and must not exceed 2.5 m if within 2 m of a boundary. Buildings other than the original house may not cover more than 50% of the curtilage. In a listed curtilage any outbuilding needs permission, and on designated land further limits apply. The 1-bedroom and 2-bedroom ranges are drawn as external dimensions; eaves and ridge figures come from the elevation drawing.
The mobile home route: annexes that meet the caravan definition
The Caravan Sites and Control of Development Act 1960 defines a caravan as any structure designed or adapted for human habitation which is capable of being moved from one place to another, whether by being towed or by being transported on a motor vehicle or trailer. Section 13 of the Caravan Sites Act 1968 extends that to twin-unit structures of not more than two sections, assembled on site by bolts, clamps or other devices, and physically capable of being moved by road when assembled. The maximum dimensions in section 13(2), as amended for England in 2006, are 20 metres in length exclusive of any drawbar, 6.8 metres in width, and 3.05 metres overall height of living accommodation measured internally.
Some councils, including Rother, state that a caravan within the domestic curtilage, used solely for purposes ancillary or incidental to the residential occupation of the main dwellinghouse, may not need planning permission for its siting. Two points keep this route honest. The same council states that independent residential occupation of a caravan or mobile home requires planning permission, so the use test applies in full. And the definition is about construction and mobility, not appearance: a unit that cannot in practice be moved as a whole has left it. Buyers confirm the position with a certificate, not an assumption.
Lawful development certificates and pre-application advice
A lawful development certificate is the formal way to settle whether a proposal needs permission. Under section 192 of the Town and Country Planning Act 1990 a council can certify that a proposed use or development would be lawful for planning purposes; section 191 does the same for an existing use or building. The Planning Practice Guidance is explicit that a certificate applies only to lawfulness under planning legislation, does not remove other legal requirements, and rests on evidence the applicant supplies. Rother District Council recommends one whenever a buyer is uncertain. That is the honest answer to the search for an annexe with no planning permission: the certificate says so for one site, and nothing else does.
Pre-application advice is the other tool. Councils may charge for it under section 93 of the Local Government Act 2003, at no more than the cost of the service. For an annexe, pre-application advice can indicate which route the council is likely to expect and what conditions may be considered, but it is not a planning permission or a certificate.
Building regulations, council tax and what changes when the relative moves out
Building regulations approval is separate from planning permission and a project may need both. The Planning Portal gives the outbuilding exemptions: under 15 square metres with no sleeping accommodation, and 15 to 30 square metres with no sleeping accommodation where the building is at least one metre from any boundary or substantially non-combustible. An annexe with a bedroom therefore normally sits within the regulations, assessed by the buyer’s building control route on the project drawings.
| Question | What applies in England |
|---|---|
| Council tax band | Each self-contained unit receives its own band from the Valuation Office Agency. |
| 50 per cent reduction | Annexe lived in by immediate family of the main household, or used as part of the main residence but otherwise unoccupied. |
| Class W exemption | Annexe occupied by a dependent relative aged 65 or over, or who is severely mentally impaired or substantially and permanently disabled. |
| Relative moves out | The planning condition still binds: family or non-paying guests only. Separate letting or occupation is likely to need a fresh planning assessment or application, and a separate sale may conflict with an ancillary-use condition. |
The last row is the one buyers overlook. The ancillary condition survives the relative: an empty annexe can serve the household as a study or guest room, and a Class T exemption can apply where planning restrictions prevent separate letting, but a tenant or a separate sale is a new dwelling in the council’s eyes.
What Eurodita supplies and what stays with the buyer
Eurodita is the manufacturer. It supplies the timber kit: wall logs in the approved solid, twin-skin or glulam profiles, roof and floor structure, timber windows and doors, and the 2D floor plans, elevation drawings, window and door schedule and 3D visuals for each configured project. Where a project specifies it, the kit can be designed to a BS 3632-related brief or to the Caravan Sites Act dimensions above, as the holiday park lodge procurement guide describes. That is a manufacturing scope, not a certification, and it does not decide how a council classifies the unit on a site.
Everything that turns the kit into a lawful annexe stays with the buyer, the dealer or the project team: the planning application or certificate, building control, foundations, installation, insulation bought locally, electrical, plumbing and gas work, and the occupation arrangements that keep the annexe ancillary. Structural calculations come from specialist partners where needed. Standard cabins reach private clients through dealers; larger residential annexes are quoted directly, each project assessed individually. Dimensions are external and the base size per model is published, so drawings and kit agree before the order is placed.
Frequently asked questions
Does a granny annexe need planning permission in the UK?
In England the usual starting point is that a self-contained annexe in a garden needs planning permission, either as an ancillary annexe tied to the main house by condition or, where the structure meets the legal definition of a caravan and is used in association with the house, through a lawful development certificate confirming that no permission is needed. Wales, Scotland and Northern Ireland apply their own rules, and the Republic of Ireland has a separate system.
Can I build an annexe without planning permission under permitted development?
Rarely. Class E permitted development covers outbuildings required for a purpose incidental to the enjoyment of the house, such as a garden office or store, and the Planning Portal states it does not cover use as separate self-contained living accommodation. Sleeping accommodation for a relative is primary residential use, so a bedroom annexe is normally outside Class E even when it meets the height and coverage limits.
How big can a granny annexe be?
There is no single size limit. Under Class E an outbuilding must keep eaves to 2.5 m, overall height to 4 m with a dual-pitched roof or 3 m otherwise, 2.5 m within 2 m of a boundary, and buildings may not cover more than 50% of the curtilage. A twin-unit structure meets the caravan definition only within 20 m by 6.8 m and 3.05 m internal height. An annexe granted planning permission is sized by the council’s assessment of the plot and the relationship to the main house.
What is the difference between an ancillary annexe and a separate dwelling?
An ancillary annexe has a functional link with the main house: same ownership, same curtilage, shared access, no subdivided garden, and occupation by family or non-paying guests. A separate dwelling is occupied independently, often with its own meters, address or access. Councils assess the intended use, not just the building, and grant ancillary annexes with a condition preventing separate occupation.
Does a granny annexe need building regulations approval?
Normally yes. The small-outbuilding exemptions below 15 square metres and between 15 and 30 square metres apply only where the building contains no sleeping accommodation. An annexe with a bedroom is therefore within the regulations and is assessed by the buyer’s building control route on the project drawings. Building regulations approval is separate from planning permission.
Does Eurodita secure planning permission for an annexe?
No. Eurodita is the manufacturer and supplies the timber kit with the drawing set for each configured project. Planning, lawful development certificates, building control, foundations, installation and utilities stay with the buyer, the dealer or the project team. Where a project specifies it, a kit can be designed to a BS 3632-related brief or to Caravan Sites Act dimensions, without any certification or planning outcome being implied.
How to start a granny annexe project
Send the plot address, the intended occupant and the model or footprint in mind, with any pre-application response or certificate already held. Eurodita confirms the product route and, once the brief is configured, produces the drawing set for that project, so the buyer, dealer or project team has drawings to use before any planning route is confirmed and manufacture begins.