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Granny annexe cost: what it really costs in 2026
Per m², modular and brick-built.
£2,200 – £3,960 /m²
A modular garden annexe starts around £2,200/m². Brick-built annexes run about £3,960/m². A typical one-bed annexe of 35m² lands £77,000–£139,000.
Price by spec
| Option | What it means | Typical price |
|---|---|---|
| Modular | Factory-built, craned in | £2,200 /m² |
| Brick-built | Traditional build, matches the house | £3,960 /m² |
What actually happens
- Feasibility first — planning is the gatekeeper on annexes
- Base and services laid: water, drainage, power from the house
- Modular: unit delivered and craned on in a day. Brick: build proceeds like a small house
- Connected, insulated and first-fixed
- Kitchen and bathroom fitted
- Decoration, certification and sign-off
Popular choices
One-bed with wet roomOpen-plan studio layoutsMatching brick or contrasting cedar
Regulations to know
- Annexes for a family member usually need planning permission — the test is whether it stays 'ancillary' to the main house rather than a separate dwelling
- Building regulations apply in full: it's habitable accommodation
- Council tax treatment varies; annexes for family often qualify for a 50% discount or exemption
Tips from the trade
- Talk to the planning department before spending a pound — annexe rules vary sharply by council
- Modular wins on speed and certainty; brick wins on lifespan and blending in
Plan this project properly
Get a region-adjusted estimate, track budget against real quotes, and find local tradespeople -- free to browse on Qome.
Start planning on QomePrices on this page are approximate, region-adjusted guide figures built from cross-checked UK cost data. They exist to inform you, not to bind anyone. Actual prices are whatever you and your tradesperson agree, and a difference between a Qome guide figure and a real quote is not a fault in either.