Why do annexes need planning permission?
A self-contained annexe — with sleeping accommodation, bathroom and kitchen/kitchenette — constitutes a new dwelling under planning law. This means it falls outside the permitted development Class E outbuilding rules, which only permit incidental outbuildings (home offices, gyms, studios). The creation of a new dwelling requires a full planning application. The planning authority assesses: housing demand and supply policies; impact on residential amenity; design and visual impact; parking; the risk of the annexe becoming a separate market-rented unit. In inner London boroughs (Hackney, Islington, Camden), planning policy is often restrictive about new dwellings in back gardens due to density concerns. Outer London boroughs (Barnet, Havering, Bromley) are generally more permissive.
What conditions are typically attached to annexe planning permissions?
Most annexe planning permissions in London are granted with conditions including: (1) the annexe shall only be occupied as ancillary accommodation to the main dwelling at [address] and shall not be sold, let or occupied separately; (2) no kitchen or full cooking facilities shall be installed without further planning permission; (3) the development shall use matching materials to the main house; (4) no further outbuildings or extensions to the annexe are permitted. Condition (1) is the most significant — it prevents the annexe from becoming a separately titled property or a commercial letting. Removal of this condition (to enable sale or commercial letting) requires a separate planning application.
How to design an annexe that will get planning permission in London
London LPAs are most likely to approve an annexe that: is clearly secondary in scale to the main house; uses matching materials and architectural language; has limited glazing facing neighbours; does not result in overlooking of adjacent gardens; includes internal connectivity to the main house (creating an ancillary rather than independent feeling); has a clear purpose (elderly relative, adult child) and a planning statement explaining the family need; is sited to minimise impact on the garden. A planning architect experienced in your specific LPA is essential — local planning policy varies considerably, and what is approved routinely in Barnet may face objection in Camden. Pre-application advice (£150–£500 depending on LPA) is nearly always worth the cost.
Granny flat planning permission in London
A 'granny flat' or dependent relative annexe is the most common type of annexe application in London. To strengthen such an application, the design should: include an internal connecting door between the annexe and main house; omit a full kitchen (a kitchenette with microwave, fridge and sink rather than a full hob/oven is more likely to be accepted as ancillary); demonstrate that it meets accessibility needs of the occupant (level access, wider doors, wet room) — this also helps with VAT planning. Evidence of the dependent relative's need (healthcare or social care documentation) can support the planning statement. LPAs cannot legally require proof of a family member — but a well-crafted planning statement helps contextualise the application.
