A granny annexe built correctly can add significant value to your property. Built without understanding the crucial distinction between an annexe and a separate dwelling — or without checking what's on the planning record — it can create an enforcement problem that outlasts the sale.
It depends entirely on how the annexe is designed and used. The planning status of an annexe hinges on one question: is it genuinely ancillary to the main house, or is it a separate self-contained dwelling? That single distinction determines whether you need planning permission — and it\'s where most annexe projects go wrong.
An annexe that is genuinely ancillary to the main house may fall within permitted development as an outbuilding under Class E of the GPDO. It must be within the curtilage, single storey (max eaves height 2.5m, overall height 4m), not covering more than 50% of the garden area, used for a purpose incidental to the house, not forward of the principal elevation, and not on designated land.
You need a full application if the annexe is self-contained with its own separate entrance, kitchen, bathroom, and bedroom. Two-storey annexes need permission. If it is or could be separately let or sold, permission is required. Listed buildings and conservation areas also require permission. Conditions from previous permissions often restrict annexes on specific properties.
This is where more annexe projects fall foul of planning than any other issue. The council looks at physical design, not just stated intention. Factors pushing toward a separate dwelling: own front door accessible without entering the main house, a full kitchen, complete bathroom facilities, no physical connection to the main house, and the ability to be sold or let independently. Getting this wrong means an enforcement notice requiring removal at significant cost.
Permitted development outbuilding allowances count toward the 50% garden coverage limit alongside existing outbuildings, sheds, and extensions. If previous owners have already used this up, you may have less room than you think. Previous planning permissions — particularly on new-build estates — may also include conditions specifically restricting outbuildings or ancillary accommodation.
An annexe built as an outbuilding under permitted development cannot be sold separately from the main house. If your long-term plan is to give or sell the annexe to a family member as a separate property, permitted development is the wrong route — you need a planning application for a separate dwelling from the start.
Standard searches check the public register. We go further — querying live portals, blocked legacy systems, pre-merger authority databases, committee PDF archives, Land Registry title constraints, and comparable decisions across your postcode cluster. What we retrieve determines what you know before you build, buy, or appeal.