Is a Granny Annexe Worth It in 2026? (UK)
A self-contained granny annexe costs £45,000–£120,000 in 2026, depending on whether you convert an integral garage, extend the house, or build a standalone garden annexe. It is a serious sum — but the case is rarely just about resale. A well-designed annexe can add 20–30% to the property, keep an elderly relative independent yet close, and offset care-home fees that now routinely exceed £50,000 a year. Here is the honest cost-benefit, the planning and council-tax catches that change the maths, and when an annexe genuinely pays.
The verdict: cost vs benefit
| Annexe type | Typical cost (2026) | Notes |
|---|---|---|
| Garage / integral conversion | £45,000–£65,000 | Cheapest route, uses existing structure |
| Attached extension annexe | £60,000–£95,000 | Integrated, shares services |
| Standalone garden annexe | £75,000–£120,000+ | Most independence, own services |
| Care-home fees (for comparison) | £50,000+/year | The cost an annexe can offset |
When a granny annexe is clearly worth it
It pays when you are weighing it against residential care fees — a one-off annexe build can be recovered within two to three years of avoided care costs, while keeping a relative independent and close. It also pays when the annexe is genuinely flexible: today a granny flat, tomorrow a home office, guest suite, teenager's space or rental income (subject to planning). Flexible space holds its value; single-purpose space does not.
The catches that change the maths
Two things catch people out. First, planning: a dependent-relative annexe is often acceptable, but it usually cannot become a fully independent dwelling sold separately without further consent. Second, council tax: a self-contained annexe may attract its own band (with a 50% discount where occupied by a dependent relative). Factor both in before committing.
When it is not worth it
It rarely pays if the annexe is highly bespoke to one person's needs with no flexible future use, if the plot is too small so the annexe swallows the garden and dents resale, or if you would need to borrow heavily at a point where the relative may only use it briefly. Run the care-cost comparison honestly before you build.
FAQs
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