How much does a granny annexe cost?
Advertised building prices run from around £50,000 for a compact studio to £160,000 or more for a two-bedroom, and up to about £190,000 on the full planning route. Most one-bedroom annexes are priced between £70,000 and £120,000. What sits behind those figures, what they leave out, and how to compare two quotes properly.
These are advertised “from” prices, not average installed costs. The final figure depends on size, specification, which planning route is used, and what is included in the quote. Some companies include foundations in the price, and a few include a short run of services, usually 10m to 20m. Where neither is included, groundworks and mains connections typically add £15,000–£20,000 to the total.
In short
- Building price: from about £50,000 for a studio under 25sqm, £70,000–£120,000 for a one-bedroom, and £125,000–£160,000 or more for a two-bedroom. These come from The Garden Room & Annexe Guide’s October 2026 price survey of 267 published prices from 13 UK annexe specialists.
- All-in: where groundworks, foundations and mains connections are not included, they typically add £15,000–£20,000, so a realistic one-bedroom budget is £85,000–£140,000.
- VAT: 20% on the full planning route. A BS3632 annexe supplied under the Caravan Act may be zero-rated, which on a £90,000 building is a difference of up to £18,000.
- Comparing quotes: confirm VAT, groundworks and mains connections on every quote before comparing any two; the cheaper one has often just left more out.
What does a granny annexe cost in the UK?
From around £50,000 for a compact studio to £160,000 or more for a two-bedroom. Most one-bedroom annexes, typically 35–50sqm, are priced between £70,000 and £120,000.
These figures come from The Garden Room & Annexe Guide’s October 2026 price survey: 267 published prices from 13 UK annexe specialists, each checked on the specialist’s own website. All are advertised starting prices, so upgrades, site-specific costs and optional extras are not included. The right-hand column adds the £15,000–£20,000 that site preparation and connections typically add where they are not in the price.
| 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+ |
Advertised starting prices, checked October 2026. Two-bedroom annexes on the full planning route reach about £190,000 for the building. VAT treatment varies by company and route; see below.
Layouts, floor plans and real projects at each size: studio and open-plan, one-bedroom, two-bedroom and three and four-bedroom annexes.
What the October 2026 survey found
Entry prices start higher than many guides suggest. The cheapest model from each specialist starts at about £63,000 at the median. Only two of the 13 advertise anything under £50,000, and both are compact studios of 15sqm or less.
About £2,400 per square metre. Across the 11 specialists that publish sizes, the median building price is about £2,400 per square metre, and every one falls between £2,100 and £2,950. Smaller annexes cost more per square metre: around £3,100 under 25sqm, falling to around £2,000 above 55sqm.
Connections are rarely in the price. Only four of the 13 include any connection to water, drainage and electrics in the advertised price, and where they give a distance it is a short run, usually 10m to 20m.
VAT is often unclear. For five of the 13, the published prices don’t make clear whether VAT is included.
Typical published prices by route and size October 2026 prices
Choose a planning route and a floor area to see the lower end, typical price and higher end of the published starting prices for that size, and how many prices and suppliers sit behind each figure.
Granny annexe market price calculator
Step 1 · Choose a planning route
Step 2 · Select a floor area
Choose a floor area above to see typical starting prices.
Find an annexe specialist near you
Not every company works in every area. The directory lists the specialists covering your location, filtered to the route you chose above.
What these prices do and don’t include
- They are advertised starting prices. Real quotes vary with specification, site conditions and supplier. Always get at least three.
- VAT is not always stated. Some prices include 20% VAT, some do not say. A BS3632 annexe supplied under the Caravan Act may be zero-rated, which can make that route cheaper than it first appears. Confirm the VAT position with the supplier and an accountant.
- Foundations and connections are often separate. 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. Confirm what a quote covers before comparing it with another.
- The two routes are not the same product. The Caravan Act route avoids a full planning application in most cases; full planning gives a permanent, Building Regulations-certified structure. Each has long-term implications, covered below.
Why annexe prices are difficult to compare
Three things create most of the confusion: VAT, groundworks, and the word “from”.
VAT is not consistently stated
Some companies include 20% VAT in their advertised prices; others do not state it at all. At 20%, a £95,000 price becomes £114,000 inclusive. A company that includes VAT can look more expensive at first glance, or the difference can be real. Confirm the VAT position before making any comparison.
Foundations and connections vary
Foundations, site preparation and connections to mains electricity, water and drainage are the biggest wildcard in annexe pricing. Many companies now include foundations, and a few include a short run of services, usually 10m to 20m from the building. The connection back to the house beyond that is normally extra. Where both building and fully installed prices were published, site preparation and connections added £15,000–£20,000. A quote that looks cheaper on paper may simply have fewer items in it.
How the planning route changes the price
The same annexe can cost noticeably more on the full planning route than under the Caravan Act, and most of the difference is VAT.
An annexe built to Building Regulations with full planning permission is charged VAT at the standard 20%. One built to the BS3632 residential standard and sited under the Caravan Act may qualify for zero-rating under HMRC Notice 701/20; confirm with the supplier and an accountant. On the Caravan Act route a Lawful Development Certificate confirms the siting is lawful, and some companies include it in their price while others charge for it.
Annexe by Future Rooms shows the difference more clearly than most, because it publishes the price of each model on both routes. Its Hanley one-bedroom is £98,840 built to BS3632, with VAT at 0%, and £124,608 built to Part L of the Building Regulations: £103,840 for the building plus £20,768 VAT. Most of the gap is VAT. The remaining £5,000 is the step up to the Part L specification.
The route also changes what is bought. Full planning gives a permanent structure, treated as an extension in legal and mortgage terms; a Caravan Act annexe has to stay technically moveable, which is why ground-screw foundations are common. Neither is inherently better. The right choice depends on the property, the local authority, and what the buyer intends for the building in the long term.
Read more: Granny annexe without planning permission: how the Caravan Act route works →
What affects the cost of a granny annexe?
Size
Annexes are priced per building rather than strictly per square metre, but larger buildings cost more. A compact studio of around 20sqm can start from about £50,000 on the Caravan Act route; a large two-bedroom annexe of 75–80sqm can reach £160,000 or more, and about £190,000 on the full planning route. Size and price do not scale in proportion. Most of the cost is fixed, in the kitchen, bathroom, connections, delivery and installation, so a 20sqm studio typically costs 60–70% of a 40sqm one-bedroom, not half. Buyers on a firm budget are often better served by pricing the next size up before ruling it out.
Specification and finish
Base prices cover the structure and a standard specification. Kitchen fit-out, bathroom fittings, flooring, cladding and window configuration all move the final figure. Some companies offer fixed packages; others quote bespoke. A fully specified annexe with upgraded finishes will cost more than the published starting price.
Groundworks and site preparation
Many advertised prices now include foundations, but site preparation and mains connections are often extra, or covered only for a short run from the building. Ground conditions, access, the distance to existing services and how level the site is all affect the cost. Ask what groundworks allowance is built into a quote, how far the services run, and whether the company does the groundworks itself or subcontracts them.
VAT
Some companies include 20% VAT in their advertised prices; others quote ex-VAT or do not say. Caravan Act structures may qualify for zero-rating in some circumstances. Confirm the VAT position and rate before comparing any two quotes.
What is included in an annexe price?
Usually included
- The structural frame and insulation
- External cladding and roofing to a standard finish
- Windows and external doors
- Internal studwork and plasterboard
- A standard kitchen and bathroom fit-out
- First-fix electrics: consumer unit, sockets, lighting positions
- Delivery to site
Usually excluded
- Site preparation, and foundations unless explicitly stated
- Connection to mains electricity, water and drainage beyond a short included run
- Planning application or Lawful Development Certificate fees
- Furniture, white goods and accessories
Site preparation, foundations and mains connections, whatever the size of the building.
Between the advertised price and a finished annexe
Where comparable building and fully installed prices were published, site preparation, foundation installation and mains connections added £15,000–£20,000 to the building price. The figure held broadly steady regardless of size, and it is the most reliable market evidence of what sits between a starting price and a connected annexe ready to live in. Some companies offer a turnkey price that covers it all. Ask, and make sure any quotes being compared cover the same scope of work.
Can you rent a granny annexe instead?
A few specialists now rent annexes as well as selling them. You pay a one-off installation fee and a monthly rent for a fixed minimum term, then keep renting, buy the annexe, or have it collected. Rental annexes are designed as mobile homes under the Caravan Act, which is what makes them practical to remove at the end.
At the time of writing, Booths Garden Studios rent annexes from £745 a month on a 24-month minimum, plus an installation fee of £5,995 or £7,995. Renting suits a need measured in years rather than decades; over a longer stay, buying works out cheaper.
Read more: Renting a granny annexe: costs, terms and when it makes sense →
Getting quotes
Allow time to gather at least three quotes. The answers to these five questions will quickly show whether two quotes are genuinely comparable, or whether one includes items the other has left out.
- Does this price include VAT, and at what rate?
- Are groundworks and foundations included?
- Are mains connections included: electricity, water and drainage? How far from the building do they run?
- Which planning route are you proposing, and why is it right for this site?
- What does the Lawful Development Certificate process involve, and who manages it?
Find annexe specialists that cover your area
Not every company works in every area. The Garden Room & Annexe Directory lists UK annexe specialists by location, size, bedrooms and planning route.
Frequently asked questions
- How much does a granny annexe cost in the UK?
- Advertised starting prices range from around £50,000 for a compact studio to £160,000 or more for a two-bedroom annexe, and about £190,000 on the full planning route. Most standard one-bedroom annexes of 35–50sqm are priced between £70,000 and £120,000. These are starting prices; where groundworks and mains connections are not included, they typically add a further £15,000–£20,000.
- How much does a granny annexe cost per square metre?
- About £2,400 per square metre for the building, at the median across the 11 UK annexe specialists in our October 2026 survey that publish sizes. Every one falls between £2,100 and £2,950. Smaller annexes cost more per square metre, around £3,100 under 25sqm against around £2,000 above 55sqm. Groundworks and connections are extra where they are not included.
- What is the Caravan Act route for annexes?
- Annexes built to the BS3632 residential mobile home standard can be classified as mobile homes under the Caravan Sites Act 1968. No full planning application is required in most circumstances; a Lawful Development Certificate confirms the siting is lawful. Ground-screw foundations are often used so the building remains technically moveable, and some supplies on this route qualify for zero-rated VAT.
- What is the difference between a Caravan Act annexe and a full planning annexe?
- A Caravan Act annexe is classified as a residential mobile home, needs no full planning application and can usually be installed more quickly. A full planning annexe is a permanent structure requiring a planning application and Building Regulations approval, a longer process, but the result is legally equivalent to a conventional extension.
- Do I pay VAT on a granny annexe?
- It depends on the route and how the supply is structured. Standard construction attracts 20% VAT. Annexes built to BS3632 under the Caravan Act may qualify for zero-rated VAT, but this is not universally applied. Confirm the VAT position and rate with the supplier and a tax accountant before comparing quotes.
- What is not included in an annexe price?
- Advertised prices often exclude site preparation, connection to mains services beyond a short included run, planning or Lawful Development Certificate fees, furniture and white goods. Some include foundations and some do not. Where groundworks and connections are both excluded, they typically add £15,000–£20,000 to the building price.
- How big does a granny annexe need to be?
- A compact studio of 20sqm can work for occasional guest use. A one-bedroom annexe of 35–50sqm suits full-time occupation, with a comfortable bedroom, bathroom, kitchen and living area. Two-bedroom annexes of 65–80sqm suit couples or where more flexibility is needed.
Last updated October 2026 · Part of our garden annexe guide.
