Multi-Generational Living: Annexes and Extensions for Extended Families
More families in Dorset are choosing to live together across generations. A practical guide to annexes, self-contained extensions, and making multi-generational living work.
Why multi-generational living is growing
The economics are compelling. Care home fees in Dorset average £800–£1,200 per week. A self-contained annexe costs £60,000–£100,000 to build and provides better quality of life for an elderly parent while keeping them close to family. At the other end, adult children priced out of the Dorset property market (average first-time buyer house price: £280,000) can live semi-independently in an annexe while saving for a deposit. Multi-generational living also provides built-in childcare, companionship, and shared household costs. It is not a new idea — it was the norm for centuries. The detached nuclear family home is the historical anomaly.
Annexe vs extension: the planning distinction
This matters enormously. A self-contained annexe (separate entrance, kitchen, bathroom, bedroom) used by a family member is generally treated as ancillary accommodation and may fall under Permitted Development if built within the curtilage of the house. But if the annexe could be let or sold independently, the council may classify it as a separate dwelling, requiring a full planning application and potentially CIL (Community Infrastructure Levy). The key factors are: does it share a garden with the main house? Is there internal access? Can it function without the main house? Dorset Council has published guidance on this — we can advise on how to design your annexe so it meets PD criteria while still providing genuine independence.
Design for independence and connection
The best multi-generational homes balance togetherness with privacy. A connecting door between the annexe and the main house — lockable from both sides — allows access when wanted and privacy when needed. Separate external entrances mean the annexe occupant can come and go without walking through the main house. A shared garden but separate outdoor seating areas give everyone space. Inside the annexe, a compact but complete layout is essential: a small kitchen (even if meals are often shared), a full bathroom (not just a shower room), a living area, and a bedroom. Minimum 35m² for comfortable single-person living, 45m² for a couple.
Accessibility from the start
If the annexe is for an elderly parent, design for full accessibility from day one — even if they do not currently need it. Level thresholds, wet room instead of a bath, wider doorways (900mm clear opening), lever taps and handles, a kitchen with adjustable-height worktops, and space for a wheelchair to turn (1500mm turning circle). Emergency pull cords in the bathroom and bedroom linked to an alarm in the main house provide safety without intrusiveness. These features cost 5–10% more at construction but are five times more expensive to retrofit. A Part M compliant annexe also qualifies for reduced council tax under certain circumstances.
Council tax, insurance, and legal considerations
An annexe occupied by a dependent relative may qualify for a council tax discount or exemption under the dependent relative council tax disregard — but this varies by council. Check with Dorset Council before building. Your home insurance must be updated to cover the annexe; most standard policies exclude outbuildings used as living accommodation. Buildings insurance should cover the annexe structure, and the occupant needs their own contents insurance. Legally, the annexe should not be registered as a separate title — this maintains its status as ancillary accommodation and avoids complications with lenders and at resale.
Written by the PlanBuildCo team
9 years designing extensions and renovations in Poole, Dorset.
Ready to take the next step?
Related articles
Permitted Development Rights: What You Can Build Without Planning Permission
A plain-English guide to what you can and cannot build under Permitted Development — and when you actually need to apply for planning permission.
Read articleGrowing Family? How to Extend Your Home for More Space
Practical advice on extending your home to accommodate a growing family — from extra bedrooms to open-plan living, play areas, and future-proofing your layout.
Read articleExtending a Bungalow: Upwards, Outwards, or Both?
Bungalows offer a unique set of extension possibilities — including going upward to create a chalet-style home. A practical guide to bungalow extensions in Dorset.
Read articleReady to start your project?
Professional plans from £250. No obligation, no follow-up calls.
Every plan drawn by qualified drafters in Poole, Dorset
Serving homeowners across Poole, Bournemouth, Christchurch, Wimborne, Wareham, and the wider Dorset area.