Garden annexes: a complete UK guide
A garden annexe (also spelt annex), often called a granny annexe, is self-contained living accommodation in your garden: its own front door, kitchen, bathroom and sleeping space. This page covers the decisions that matter most before you speak to any company, and links to the full guide on each.
Building a garden annexe is a significant project, and a different one from adding a garden room. Most people searching for one call it a granny annexe, and the two names are used interchangeably here. The two things that shape every decision are the planning route and the standard the building is held to, because an annexe is habitable accommodation, not an outbuilding. Below is the shape of it; each section hands off to the full guide on that topic.
In short
- What it is: a self-contained home in the garden, with its own kitchen, bathroom and bedroom, built to a residential standard. “Granny annexe” and “granny pod” describe the same building. What is an annexe? →
- Planning: it can never go up as an ordinary garden building. It needs either full planning permission with Building Regulations, or to qualify as a caravan under the Caravan Act route, usually confirmed by a Lawful Development Certificate.
- Cost: a compact studio from about £50,000, a one-bedroom £70,000–£120,000, a two-bedroom £125,000–£160,000 or more. Where they aren’t included, groundworks and mains connections typically add £15,000–£20,000.
- Who builds them: experienced annexe specialists who offer a turnkey service, from planning to handover, rather than companies who only take on part of the work. Most travel to you, so there is more choice than whoever is based nearby.
How a garden annexe differs from a garden room
From the outside the two can look alike. For anyone who will live there, they are not the same thing.
| Garden annexe | Garden room | |
|---|---|---|
| Use | Self-contained living accommodation | Workspace, gym, leisure, hobbies |
| Planning | Full planning permission or the Caravan Act | Usually Permitted Development |
| Building standard | Building Regulations (or BS3632, usual on the Caravan Act route) | Often exempt up to 30sqm if no one sleeps in it |
| Typical cost | £50,000–£160,000+ | £20,000–£50,000 |
| Sleeping | The core purpose | Not intended |
A garden room with a kitchenette and a shower added is still a garden room unless it has been built for someone to live in and has been through one of the two planning routes.
Who a garden annexe is for
An older parent or relative
The classic granny annexe: independent accommodation close to family, without anyone giving up their space. Most companies can build in the details that make it work long-term: level access, wide doorways, a properly specified bathroom.
A young adult
A separate front door and real independence, whether they are saving for a deposit or coming home after a few years away.
A relative with a disability or mobility need
The project where the detail matters most, and where the right layout, built in from the start, makes the biggest difference.
Guests or letting
Its own front door, kitchen and bathroom make it a very different thing from a spare bedroom. Letting is a planning question, though: raise it at the start.
The right design decisions are different for each, which is why this guide covers who will live there, not just what gets built.
Find granny annexe specialists working in your part of the UK
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Do you need planning permission for a garden annexe?
In effect, yes. A garden annexe can’t go up as an ordinary garden building: it needs either a full planning application, or to qualify as a caravan under the Caravan Act, usually confirmed by a Lawful Development Certificate.
A granny annexe is habitable accommodation, so the Permitted Development rights that cover most garden rooms do not apply. The two routes differ in cost, timescale, VAT and how the building is classified.
Full Planning Permission with Building Regulations
- How it works
- A planning application to the local authority; if approved, the building is constructed to Building Regulations and signed off by building control. A permanent building with planning permission.
- VAT
- Usually 20%: HMRC standard-rates an annexe that can’t be used or sold separately from the house.
- Timescale
- Allow 6–12 months from application to occupation.
The Caravan Act with a Lawful Development Certificate
- How it works
- The building is made as a twin-unit caravan, usually to BS3632, the residential park home standard, and sited within the curtilage of the house, used as part of the main home. No planning application; a Lawful Development Certificate confirms the siting is lawful.
- VAT
- May qualify for zero-rating, a difference of up to £18,000 on a £90,000 building. Confirm in writing and take advice.
- Timescale
- Usually faster for a straightforward site.
Neither route is inherently better. What matters is a company that is honest about which suits your site, and why. Some specialists submit both applications at once where a site is uncertain.
How big is a granny annexe?
From compact studios to house-scale three-bedroom buildings. Most companies offer modular ranges that step up in 500mm increments; bespoke designers work to the exact dimensions the garden allows.
| Layout | Typical size | Best for |
|---|---|---|
| Studio / open-plan | 16.5–51 sqm | A flexible single space |
| One-bedroom | 21–88 sqm | The most popular layout: genuine independence |
| Two-bedroom | 44–85 sqm | A couple, a live-in carer, or letting |
| Three / four-bedroom | 60–100 sqm+ | House-scale, multigenerational |
How garden annexes are built
A granny annexe is built for year-round living: to Building Regulations on the planning route, and usually to BS3632, the residential park home standard, on the Caravan Act route. The two most common construction systems are timber frame and SIPs (structural insulated panels), both drawn from modern UK house building: a timber frame is built up from studwork and insulated on site, while SIPs arrive as factory-made insulated panels, strong on thermal performance and quick to assemble. Steel frame and interlocking timber are also used.
The system matters less than the specification it is built to and the company’s experience with habitable accommodation. On the Caravan Act route the building is made in no more than two sections, joined on site, and once assembled it must still be capable of being moved by road: a design constraint engineered into the structure and invisible in the finished building.
Designing an annexe around the person living in it
The most important design decisions are less about looks and more about how the building works day to day, and over time.
Level access throughout
The single most important feature for an older or less mobile occupant, and much harder to add later: a flush threshold at the door, no steps inside, and a walk-in shower or wet room rather than a tray.
- Pocket doorsRecover the floor space a door swing takes; they are easiest to design in from the start.
- A well-specified bathroomReinforced walls for future grab rails, a rooflight for natural light, a level-access shower.
- Specify from the outsetHeating, broadband and any future provisions are simple at the design stage and disruptive to add later.
- Light and orientationWhere the glazing faces decides how the living space feels through the year; ask to see the plan on the site, not just the brochure.
How much does a granny annexe cost?
From about £50,000 for a compact studio to £160,000 or more for a two-bedroom, before groundworks and connections.
| Layout | Building | Realistic all-in |
|---|---|---|
| Studio / open-planunder 25 sqm | £50,000–£75,000 | £65,000–£95,000 |
| One-bedroom31–55 sqm | £70,000–£120,000 | £85,000–£140,000 |
| Two-bedroom55–90 sqm | £125,000–£160,000+ | £140,000–£180,000+ |
Based on 267 published prices from 13 UK annexe specialists, checked October 2026. A two-bedroom on the full planning route can reach about £190,000. Some companies include foundations in the price, and a few include a short run of services, usually 10m to 20m. Connecting to the water, drainage and electrics at the house beyond that is normally extra. Where neither is included, groundworks and connections typically add £15,000–£20,000. Some prices include VAT and some do not, so confirm what each quote covers before comparing any two.
Running costs: council tax
A self-contained annexe can be given its own council tax band. There are discounts and exemptions that may reduce or remove the bill, depending on who lives there and where in the UK you are, so check with your council before you build.
How to choose a granny annexe company
An annexe is a different project from a garden room, so look for an experienced annexe specialist offering a turnkey service: planning, groundworks, build, connections and handover under one roof, rather than a company that takes on part of the work and leaves the rest to you. Many of the specialists in the directory build garden rooms too; what matters is a track record of finished, occupied annexes. Most run installation teams that cover a wide area, so there is more choice than whoever happens to be based nearby.
- How many annexes have you completed in the last two years, and can I visit one?
- Which planning route do you use, and why is it right for my site?
- Does your price include VAT, and what will I need to budget separately?
- Who manages the planning consent, or the Lawful Development Certificate, and the building sign-off?
Find annexe specialists that cover your area
The Garden Room & Annexe Directory lists UK companies that build annexes, filtered by location, size, bedrooms and planning route.
Official guidance
This page explains the rules in plain English. The official wording is in these sources, and where a council takes a different view of a particular case, the council decides, subject to appeal. An experienced annexe designer will walk you through the routes at the design stage, and planning consultants can advise where a site is less straightforward. But as the householder, it’s your responsibility to confirm your own position.
- Permitted development rights for householders: Technical Guidance
- Why a bedroom, a kitchen or a bathroom isn’t covered by the Permitted Development rules for garden buildings (Class E).
- Caravan Sites and Control of Development Act 1960, section 29
- The legal definition of a caravan, on legislation.gov.uk.
- Caravan Sites Act 1968, section 13
- Twin-unit caravans: no more than two sections, movable by road once assembled, and the 20m × 6.8m × 3.05m limits.
- Caravans Act (Northern Ireland) 2011, section 15
- The same twin-unit definition and limits in Northern Ireland.
- Lawful development certificates (GOV.UK guidance)
- What a certificate confirms, how to apply and how long the council has to decide.
- Building Regulations 2010, Schedule 2
- The exemptions for small buildings, which don’t apply where there’s sleeping accommodation.
- HMRC VAT Notice 701/20: caravans and houseboats
- When a caravan annexe can be zero-rated: the size test and BS 3632.
- Council Tax (Reductions for Annexes) (England) Regulations 2013
- The 50% reduction for annexes used by family in England. More in our council tax guide.
Frequently asked questions
- Do you need planning permission for a garden annexe?
- In effect, yes. A self-contained home can’t be built as an ordinary garden building. A building with its own kitchen, bathroom and sleeping space is not covered by the Permitted Development rights that apply to garden rooms. Approval comes through one of two routes: full planning permission with Building Regulations, or the Caravan Act with a Lawful Development Certificate.
- Is a garden annexe the same as a granny annexe or granny pod?
- Yes. They describe the same thing: self-contained living accommodation in the garden. “Granny annexe” and “granny pod” simply reflect who it is often built for.
- How much does a garden annexe cost?
- From around £50,000 for a compact studio to £160,000 or more for a two-bedroom, before groundworks and connections. Where they aren’t included, these typically add a further £15,000–£20,000. A realistic all-in budget for a one-bedroom is £85,000–£140,000.
- Can you live in a garden annexe permanently?
- Yes, where it has been built and consented as habitable accommodation. Most are approved as ancillary accommodation, tied to the main house and occupied by someone connected to the household.
- Can a garden room be used as a granny annexe?
- Not as it stands. A garden room is an outbuilding for uses incidental to the house, like an office, gym or hobby room, not for living in. To be lived in, a building needs one of the two planning routes and a specification for year-round living (Building Regulations, or usually BS3632 on the Caravan Act route), and it is usually far simpler to build an annexe from the start than to convert a garden room.
- Do garden annexes pay council tax?
- Usually a garden annexe is assessed for council tax in its own right, separately from the main house. In England and Wales an annexe occupied by a dependent relative may be exempt, and in England a 50% reduction applies where the annexe is a relative’s main home, or is used by someone in the main house as part of their own home. The rules depend on your circumstances and differ in Scotland and Wales, so confirm the position for your build with your local council and the Valuation Office (part of HMRC) in England and Wales, or the Assessor in Scotland. Council tax on an annexe: where to check →
Last updated October 2026.
