Do I Need Planning Permission for an Annexe 2026? (UK)
A self-contained annexe used as a separate home almost always needs full planning permission in 2026. The deciding factor is whether the annexe is ancillary to your main house or an independent dwelling. An ancillary annexe used by the same household can sometimes fall under Permitted Development, while anything with its own independent living, sleeping and cooking that could be sold or let separately needs consent. Here is exactly what needs permission, what does not, and how to get approval.
When an annexe needs planning permission
You will need full planning permission for any self-contained annexe — one with its own kitchen, bathroom and entrance that could function as an independent dwelling. Creating a separate planning unit is a material change of use, so it always needs consent regardless of whether the building itself is new or a conversion.
When it usually does not
An ancillary annexe — extra accommodation genuinely used as part of your existing household, such as a bedroom and bathroom for a relative without independent living — can sometimes be built under Permitted Development as an outbuilding, provided it stays within size, height and siting limits and is within the curtilage of the house. Conservation areas, listed buildings, Article 4 directions and flats are exceptions where PD rights are restricted or removed.
How to check if your annexe needs permission
1. Decide ancillary or independent
Will it be used by your household, or as a fully separate home? This is the single biggest factor.
2. Check size and siting
Footprint, height (especially within 2m of a boundary) and position must stay inside Permitted Development limits for outbuildings.
3. Check your designation
Conservation area, listed building, Article 4 zone or a flat? Any of these restricts or removes PD rights.
4. Apply or prove it is lawful
Submit a householder application for a self-contained annexe, or apply for a Lawful Development Certificate to confirm an ancillary one is exempt.
Costs and timescales
A householder planning application in England is £258 in 2026; a Lawful Development Certificate is £129. Add £800–£2,000 for drawings and supporting statements. Expect an 8-week statutory determination, often 10–12 weeks in practice. Building Regulations approval is separate and always required for a habitable annexe.
FAQs
Related guides
Get 3 Free Quotes — Vetted UK Builders
BestBuilders matches you with up to 3 vetted UK builders for annexes and outbuildings. Compare quotes — no cost, no obligation.