Annexe Extensions
An attached annexe: a self-contained wing built onto the main house, with its own entrance and living space but a connecting door to the family. For day-to-day care and shared meals, attached beats a garden building, and it usually adds the most resale value per pound spent.
Is this the right service for you?
This route suits families where the relative needs more day-to-day support, where the garden is too small for a separate building, or where long-term property value matters most. It costs more than modular and takes longer, but the result is one bigger, more flexible house.
What's Included
Designed for connection and privacy
Own entrance, kitchenette and wet room for independence; a connecting door and shared utility spine for practicality. Getting this balance right is the whole game.
Planning as a householder application
Extensions follow familiar householder planning rules, and an attached annexe often reads as ancillary accommodation more easily than a separate building, a genuine planning advantage.
Accessible design built in
Ground-floor living, level access, wet rooms and doorway widths to accessibility standards, designed in from the start rather than retrofitted after a fall.
Strongest value retention
Attached, consented, building-regs extensions are what surveyors and lenders understand best. At resale, the space works as an annexe, a bigger family home, or both.
Costs and trade-offs of building attached
Extension costs currently run roughly £2,200-£3,500 per square metre depending on region and spec, so a 30-40 sqm single-storey annexe extension typically lands between £70,000 and £140,000 including the bathroom and kitchenette. That is more than modular, and the build lives with you for 4-6 months.
What you get for the premium: the annexe shares the house's heating, services and structure; care becomes a corridor away rather than a walk across a wet garden; and the space integrates back into the main home effortlessly when needs change.
The main risks are the standard extension risks: party wall agreements, build cost inflation, and living through construction. A fixed-price contract with a staged payment schedule and a contingency of 10-15% keeps them manageable.
Common Questions
Is an attached annexe cheaper than a garden annexe?
Usually not. At £2,200-£3,500 per sqm, an attached annexe typically costs £70,000-£140,000 against £40,000-£85,000 all-in for a comparable modular garden annexe. The premium buys integration, care proximity and stronger resale value.
Does an annexe extension need its own council tax band?
It can, if fully self-contained. The same reliefs apply as for any annexe: full exemption when occupied by a dependent relative (65+ or disabled) and a 50% discount for other family use. The connecting door does not prevent separate banding; self-containment is judged on facilities.
What about two-storey annexe extensions?
Possible, and useful on tight plots, but stairs undermine the later-life case, and two-storey extensions face tighter planning scrutiny on neighbour impact. Most annexe extensions are single-storey for good reason: the accessible ground-floor layout is the point.
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