Granny Annexe Cost
What a self-contained annexe for a parent costs to build in the UK, by size and by finish.
Get a quotePrice your annexe
Choose a layout, set the floor area and pick a finish. The guide price moves as you do.
One-bedroom annexe, 32 m², a step up
£81,500 to £93,000
Including VAT. In London and the South East, allow 20 to 40% more.
Get a quoteA guide, not a quote. National figures for a finished annexe on firm, level ground. Your choices go with you to the form.
What moves the price
Floor area does most of the work, yet two one-bedroom annexes of the same size can sit £30,000 apart.
The finish makes up the rest. A level wet room costs more than a shower tray and earns it back for anyone unsteady on their feet. Then there is the ground: a soft or sloping plot needs deeper foundations before anything else starts.
Costs outside the builder's price
The lines families tend to meet late. Budget for them on day one.
| Cost | Guide figure | What to know |
|---|---|---|
| VAT | Included | Our figures include it at 20%. Some adaptations for a disabled person are zero-rated. |
| Planning application | £548 | The householder fee in England, from April 2026. |
| Lawful development certificate | £274 | The usual paperwork for a mobile-home style annexe. |
| Soft ground or nearby trees | Priced after a survey | Clay near trees may need an engineered raft or piles, adding several thousand pounds. |
| Water, drains and power | Priced on site | The length of trench from the house decides it. |
| Council tax | Half its own band | In England, when a relative lives there. Nothing at all for a dependent relative aged 65 or over. |
Where these figures come from
Build prices are our own national guide ranges, drawn from published UK builder price guides. Fees and tax rules are set by the bodies below; council tax rules shown are for England.
From first sum to moving in
Settle the planning route
Most annexes need a householder application; a mobile-home style unit may need only a certificate.
Fix who it is for
One person or two, a carer staying over, a wheelchair now or later. The layout sets the floor area.
Have it priced on site
A firm checks the garden, access and ground, then gives a written price.
Build
A factory-built annexe is usually finished on site within weeks. Brick and block takes a few months.
Granny annexe cost questions
How much does a granny annexe cost in the UK?
Most finished annexes cost £40,000 to £100,000 including VAT. As a national guide that is £2,200 to £3,200 per m² of floor, which puts a 20 m² studio at £44,000 to £64,000. A 45 m² two-bedroom annexe usually runs past £100,000, at £99,000 to £144,000.
Do you pay VAT on a granny annexe?
Yes, at 20%. The zero rate for new homes does not reach an annexe that cannot be sold apart from the main house. Our figures include it. Ask every firm whether its price does, because some headline prices leave it out.
Does a granny annexe need planning permission?
Usually. Permitted development covers garden buildings used for hobbies and storage, not somewhere to sleep, cook and wash. Our planning guide explains the application and the mobile-home route.
Will the annexe get its own council tax bill?
A self-contained annexe is normally given its own band. In England the bill is halved when a relative lives in it, and cancelled when that relative is dependent: 65 or over, or disabled.