The short answer
A granny annexe in the UK typically costs between £40,000 and £100,000 for a traditional build with a kitchen and bathroom. A prefab annexe is usually less, and a PrefabX Flip annexe starts from £25,000 for a compact layout and £28,000 for a two bedroom version, delivered finished and installed.
Why annexes cost more than a garden room
An annexe is a complete small home, not a single room. It needs a bedroom, a bathroom and a kitchen, plus the insulation, heating and drainage to live in comfortably all year. That is why it sits above a plain garden office on price.
It is still far cheaper than the alternative many families face, which is years of residential care fees, and it keeps a relative close rather than moving them away.
What drives the cost
The main variables are size and how the annexe is built.
- Number of rooms and overall floor area
- Kitchen and bathroom specification
- Groundwork, drainage and connecting services
- Whether it is a traditional build or a prefab building
- Planning and building control fees
Prefab versus traditional build
A traditional annexe build can run from £40,000 to well over £100,000 and take months on site. A prefab annexe is manufactured off site and installed in days, which removes much of the labour cost and the time, and gives a fixed price rather than an open ended one.
For most families the prefab route is faster, cheaper and far less disruptive, with the relative able to move in within weeks.
The Flip annexe price
A PrefabX Flip annexe is a fixed price from £25,000 for the compact Mini and from £28,000 for the two bedroom Classic, fully fitted with kitchen, bathroom, heating and electrics, and installed in 2 to 3 days.
Planning permission is usually needed for an annexe, which we factor in and guide you through, so the cost and the process are both clear before you order.
Key takeaways
- Traditional annexes run roughly £40,000 to £100,000 plus
- A prefab annexe is usually cheaper and far faster to install
- A Flip annexe starts at £25,000, fully fitted
- Cost is a fraction of years of residential care fees
Get a fixed price for your build.
Tell us what you are planning and we will recommend the right Flip layout, confirm your planning position, and give you one all inclusive price. No obligation.
Common questions
Frequently asked
Over a few years, almost always. Residential care can cost tens of thousands of pounds a year, while an annexe is a one off cost that keeps a relative independent and close to family.
With a PrefabX Flip annexe, yes. The fixed price includes the fitted kitchen, bathroom, heating and electrics, so it lives like a complete home from day one.
An annexe usually needs planning permission and building control, which carry fees. We factor these into the picture and guide the applications so there are no surprises.
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