Do you need planning permission for a granny annexe?

If the finished annexe will be self-contained, with its own kitchen, its own bathroom and a front door somebody can use without going through the main house, planning law treats it as living accommodation in its own right. That sits outside the smaller category of work a council allows without an application, so you need to apply and wait for a decision before you build. The route below follows the questions a planning officer works through, in order.

Permitted development is the general permission Parliament has already given for modest work to a house, without an application. It covers garden buildings such as sheds, studios and summer houses, as long as they are used for something "incidental" to the house and stay within limits on height and how much of the garden they cover. The government's technical guidance on householder permitted development is clear that this does not cover using an outbuilding as a bedroom, a bathroom or a kitchen. So a new garden building where your parent will sleep needs a planning application, however small it is.

An internal conversion is different. The Planning Portal's guidance on garage conversions says planning permission is not usually required where the work is internal and does not enlarge the building. A garage or spare room turned into a bedroom and sitting room for a parent, who still shares the family's kitchen, can often go ahead on that basis. Some newer homes have had these rights removed by a condition on the original planning permission, and none of this applies if the house is listed, so check with the council first.

Building regulations are a separate approval from planning permission, and they apply to almost any annexe somebody will live in, whether or not planning permission was needed for it. They cover the things that keep a person safe once they have moved in: fire safety, insulation, ventilation, and how the kitchen and bathroom are wired and plumbed. Gov.UK's planning permission guidance is the government's own starting point, and your council's planning department will confirm the position for your own project before you commit to a design.

If you are weighing up which type to build, how much it would cost to build a granny annexe sets typical build costs for each of these against each other.

The first test is the legal definition. The Caravan Sites and Control of Development Act 1960 defines a caravan as a structure designed or adapted for people to live in that can be moved from one place to another, whether towed or carried on a vehicle. The Caravan Sites Act 1968 extends that to twin-unit homes made of no more than two sections bolted together on site, provided the whole thing can still be moved by road once assembled, and sets maximum sizes for them. The limits below have applied in England since 2006, in Wales since 2007 and in Scotland since 2019.

A building on brick foundations, or one that could not be moved in one or two pieces, is not a caravan whatever the supplier calls it, and it is treated as a new building.

The second test is how it is used. The Town and Country Planning Act 1990 says that using land within the garden of a house for a purpose incidental to the enjoyment of the house is not development, so it needs no planning permission. The 1960 Act takes the same approach to site licences: no caravan site licence is needed where the use is incidental to the house in whose garden the caravan stands. The closer the arrangement is to a parent living as part of the family, sharing meals and bills, the stronger that case is. A caravan used as a separate home with its own address and post, or let to somebody outside the family, is a different use and needs permission.

Groundworks, a raised deck, new drainage connections or a driveway for the delivery can each need permission or building regulations approval in their own right, even where the caravan itself does not.

This page keeps the mobile home route to a summary.

"Ancillary" means the annexe is used as part of the household in the main house, rather than as a separate home. Councils add the condition because a self-contained annexe could otherwise be let or sold on its own, which would create a new house in a place where the council might have refused one. The government's model wording, kept in Appendix A of Circular 11/95, says the building "shall not be occupied at any time other than for purposes ancillary to the residential use of the dwelling" named in the permission. Your council's wording may differ, so read the decision notice when it arrives.

The condition also matters for council tax and for value. A self-contained annexe can be rated separately for council tax, with discounts and exemptions when a relative lives there, and do granny annexes add value covers what a buyer is likely to pay for a house with an annexe tied to it.

1. 1

   Ask the council before you finalise the design

   Before you apply

   Ask whether your council offers pre-application advice and what it charges. For a mobile home or an internal conversion, a lawful development certificate gives you written confirmation that no planning application is needed. Both are worth having if a parent is moving in soon and you cannot afford a delay.
2. 2

   Submit a householder planning application

   Fee and timescale

   In England from 1 April 2026 the fee is £548 to extend or alter a house, and £272 for a building in the garden for purposes ancillary to the house. The council confirms which applies. Most applications are decided within 8 weeks.
3. 3

   Apply for building regulations approval separately

   Before building starts

   This runs alongside or after planning permission and cannot be skipped for an annexe built or converted for somebody to live in, even one that did not need planning permission.
4. 4

   If you are refused, amend or appeal

   If it goes wrong

   Ask the council what changes would make the scheme acceptable and submit a revised application, which now pays the full fee again in England. You can also appeal to the Planning Inspectorate, free of charge, within 12 weeks of the decision letter.

The figures come from the Planning Portal's guide to fees in England from 1 April 2026. The 8 week target is on Gov.UK's after you apply page, which gives 13 weeks only for unusually large or complex applications. The free resubmission that used to follow a refusal was removed by the 2023 amendment to the fees regulations, and the 12 week appeal window and the absence of an appeal fee are on Gov.UK's householder appeals guide.

The Scottish rules are in the Scottish Government's householder permitted development guidance, and the Scottish certificate is set out in section 151 of the Town and Country Planning (Scotland) Act 1997. The Welsh limits are on the Welsh Government's outbuildings page, and the lawful development certificate under section 192 applies in Wales as it does in England. Fees in both nations are set separately from England's, so check the figure with your council before you apply.

For local council guidance, see the pages for Scotland and South Wales.