Short answer
An insulated garden room you can use all year usually costs £1,500 to £2,200 per m² fully installed, as of October 2026. That’s roughly £8,000 to £20,000 for a 3m x 3m room and £16,000 to £45,000 for a 5m x 4m one, depending on spec and where you live. Kits start far lower, but you then pay separately for the base, the electrics and your own time, and most quotes leave out something you’ll need.
All prices here are as of October 2026. They come from published 2026 cost guides, supplier price lists and owners posting on forums. Several guides don’t say whether their figures include VAT, and we flag that where it matters. Treat the guide figures as indicative: they’re blended estimates, not survey data.
Garden room cost by size
Most installed, insulated garden rooms fall between £8,000 and £45,000. Size matters, but spec and what’s included move the price just as much. Two 2026 guides publish prices by exact size, and they don’t agree, so we show both.
| Size | Floor area | less.co.uk (April 2026) | BestBuilders (Sept 2026) | Other 2026 figures |
|---|---|---|---|---|
| 3m x 3m | 9m² | £8,000–£18,000 | £12,000–£20,000 | The Garden Room Guide: £21,646 average starting price |
| 4m x 3m | 12m² | £10,000–£24,000 | £18,000–£28,000 | MyBuilder 12m²: £18,000–£24,000 |
| 5m x 3m | 15m² | £12,000–£30,000 | Not given | MyJobQuote 9–15m² band: £16,000–£38,000 |
| 5m x 4m | 20m² | £16,000–£40,000 | £30,000–£45,000 | MyBuilder 20m²: £40,000–£50,000 |
| 6m x 4m | 24m² | Not given | Not given | MyJobQuote 18–24m² band: £26,000–£50,000 |
No guide we found prices a 6m x 4m room on its own. At £1,500 to £2,200 per m², 24m² works out at about £36,000 to £53,000 (our calculation). A 6m x 4m room is also over 15m², which brings in a building regulations condition covered further down.
BestBuilders says its size table includes foundations, electrics, insulation, glazing and VAT, though one of its own graphics says VAT is excluded. less.co.uk calls its figures fully installed but doesn’t say whether VAT is in. The Garden Room Guide’s £21,646 is an average of starting prices across more than 50 ranges, including VAT, foundation and installation. It sits above the other two, and the page doesn’t list which ranges it covered.
Cost per m² by spec level
Most year-round rooms land at £1,500 to £2,200 per m² installed. Three 2026 guides agree on that middle band, even though they label the tiers differently.
| Spec level | BestBuilders (Sept 2026) | MyJobQuote (Oct 2026) | What the guides describe |
|---|---|---|---|
| Basic | £1,000–£1,400/m² | £1,700/m² | BestBuilders means summerhouse grade. MyJobQuote means standard cladding, simple doors and basic insulation |
| Mid / standard insulated | £1,500–£2,000/m² | £1,900–£2,000/m² | Good insulation, double glazing, timber cladding |
| High spec / premium | £2,000–£2,500/m² | £2,200/m² | Cedar or oak cladding, bifolds or skylights, better finishes |
| Premium bespoke | £2,500–£3,500+/m² | Not given | Architect-led or fully bespoke builds |
MyBuilder gives a wider overall band of £1,200 to £2,500 per m² for a professional build. BestBuilders says most builds fall at £1,700 to £2,200 per m².
Don’t compare these with older per-m² figures. Homebuilding & Renovating’s £360 to £840 per m² dates from June 2023 and is for budget, basic garden rooms.
Does cost per m² go up or down with size?
For the same spec, cost per m² falls slightly as a room gets bigger. Price guides often seem to show the opposite, because their bigger rooms are usually better specified.
The guides contradict themselves here. MyBuilder’s text says cost per m² “tends to drop slightly as the build gets larger”. Divide its own size table by floor area, though, and the rate rises: about £1,170–£1,500 per m² at 6m², £1,500–£2,000 at 12m² and £2,000–£2,500 at 20m². BestBuilders says price per m² “actually falls” with size, but its table is almost flat: £1,330–£2,220 at 3m x 3m and £1,500–£2,250 at 5m x 4m.
Both statements can be true. The text describes the same building made bigger. The tables describe the rooms people actually buy at each size.
Here’s why a bigger room of the same spec costs less per m². Some costs barely change with floor area: the door set, the consumer unit, the cable run from the house, delivery and getting a crew to site. BestBuilders puts a standalone electrics package (sockets, lighting and consumer unit) at £1,000 to £2,500 and the cable run at £400 to £1,500. Spread £2,000 of electrics over 9m² and it adds about £220 per m². Over 20m² it adds £100 per m².
Here’s why the tables still rise. Bigger rooms tend to come with bifolds, more glazing, air conditioning or a WC. And once a room passes 15m² of internal floor area, it must sit at least 1m from every boundary or be built substantially of non-combustible material to stay exempt from building regulations (legislation.gov.uk). Some buyers pay to meet that.
So for budgeting: price your spec per m², then expect a small room to cost a bit more per m² than a big one.
Kit, installed or bespoke
A kit is the cheapest way in, but “kit price” and “installed price” measure different things. Compare totals, not headlines.
| Route | Typical 2026 price | What you get | Source |
|---|---|---|---|
| Uninsulated shed or summerhouse | £2,000–£5,000 | Timber shell, not insulated | less.co.uk |
| Insulated flat-pack you build | £5,000–£12,000 | Panels, doors, windows; you or a builder assemble it | less.co.uk |
| Flat-pack or kit | £6,000–£15,000 | As above, wider band | BestBuilders |
| Modular, factory-built | £15,000–£30,000 | Delivered in sections and installed | BestBuilders |
| Bespoke, built on site | £12,000–£30,000 (less.co.uk); £30,000–£100,000+ (BestBuilders) | Designed and built to your plot | less.co.uk; BestBuilders |
The two guides disagree on bespoke prices by a wide margin, which tells you how loose the word is. less.co.uk says a flat-pack saves roughly £3,000 to £8,000 against a fully installed bespoke room. MyJobQuote puts a DIY garden room at £3,000 to £10,000, about 30 to 40% less than using an installer.
Watch what “installed” means on a kit listing. Gardensite sells the Forest Xtend 4.0 garden office at £12,384.99 as self-assembly, including VAT, or £15,149.99 installed (the page doesn’t say whether that includes VAT). The installed option is assembly only. The base must be ready beforehand, and the electrics aren’t supplied (Gardensite).
Insulated vs uninsulated
Pay for insulation if you want to use the room from November to March. Uninsulated rooms are much cheaper, and owners consistently say they’re cold.
An uninsulated shed or summerhouse costs £2,000 to £5,000 (less.co.uk). Upgrading a basic shell to full insulation adds £1,500 to £4,000, according to both BestBuilders and MyJobQuote.
Owners on Mumsnet are blunt about the gap. One said an uninsulated room “will be unusable for most of the year” (Mumsnet, 2025). Another, pricing an uninsulated unit of roughly 4m x 4m at “about 4 grand”, said it “will be miserable in the winter” (Mumsnet, 2025). Even the owner of an insulated £4,000 plug-in pod said it was “still cold in winter” (Mumsnet, 2023).
There’s no legal insulation standard for a typical garden office. Part L energy rules don’t apply to stand-alone buildings other than dwellings under 50m² (Planning Portal). So check the spec sheet yourself. less.co.uk suggests 50mm to 100mm of PIR or phenolic board in the walls and 100mm or more in the roof.
What’s in a quote and what’s extra
A headline price often covers the building and nothing under or behind it. The base and the power supply are the two items left out most often.
| Item | Often in the headline price? | Typical cost if extra (2026) | Source |
|---|---|---|---|
| Groundworks and base | Often not | £1,000–£3,000; £1,000–£2,000 on a flat, accessible plot | less.co.uk |
| Foundations, wider range | Often not | £1,500–£5,000; up to about £4,500 on sloped or clay ground | MyBuilder |
| Base rate per m² | – | Ground screws £30–£50/m²; concrete slab £80–£120/m² | MyBuilder; BestBuilders |
| Site preparation | Varies | £500–£2,500 | MyJobQuote |
| Cable run from the house | “Often excluded” | £400–£1,500 | BestBuilders |
| Fully wired room with consumer unit | Varies | £2,000–£3,000 | MyBuilder |
| Panel heater | Sometimes | £150–£500 | BestBuilders |
| Air conditioning | Rarely | £1,500–£3,000 | less.co.uk |
| WC | No | £1,500–£2,500 | less.co.uk |
| Shower and toilet | No | £3,000–£8,000, plus £200–£500 for a building regulations application | MyBuilder |
| Delivery | Varies | Some suppliers charge beyond about 100 miles, at around £6 a mile; some kit sellers include mainland delivery | The Garden Room Guide; Gardensite |
| Lawful development certificate | Only if you want one | £136, half the £272 planning fee (see below) | GOV.UK |
| VAT | Should be | 20% standard rate | HMRC VAT Notice 708 |
| Contingency | Never | Hold back 10–15% | BestBuilders |
Electrics. Running power to a garden room is notifiable work under Part P, and the small-building exemption doesn’t cover it. A registered electrician (NICEIC, NAPIT or ELECSA) can self-certify it. Otherwise building control has to inspect it (Homebuilding & Renovating; Planning Portal).
VAT. HMRC says construction of a new building is “normally standard-rated”. It gives a granny annexe that can’t be used or sold separately from the main house as an example of work that can’t be zero-rated (HMRC VAT Notice 708, paras 2.1 and 3.2.2). Ask every installer to show VAT on the quote.
Planning fees. Most garden rooms in England go up without planning permission under permitted development, provided they stay within the limits. One example: a maximum height of 2.5m within 2m of a boundary (Planning Portal). If you want proof, a lawful development certificate for proposed work costs half the full application fee. From 1 April 2026, the national fee for putting up a building within the curtilage of a house (category 7) is £272 (GOV.UK fee schedule). A garden room falls in that category, so a certificate costs £136 as of October 2026. Check your council’s fee page before you pay.
Payment terms. The Garden Room Guide says deposits of up to 50% are common, with about 45% due before installation and the balance on completion. Lead times of about 12 weeks are typical (The Garden Room Guide).
Where the money goes in a 12m² room
We couldn’t find a single 2026 source that splits one typical 4m x 3m quote into room, base, electrics and extras. Stitching together figures from different guides would give a false picture, so we haven’t. MyJobQuote does publish a component-by-component supply cost for a 12m² room, plus a labour estimate, and that’s what the chart shows.
Three things stand out. First, labour (£5,000 to £9,000 over two to three weeks) is the largest single line, which is why kits look so much cheaper. Second, the base is a small share of the total on a flat site, though it can cost far more on a slope. Third, MyJobQuote’s total of £18,420 to £32,200 sits well above less.co.uk’s £10,000 to £24,000 for the same size. That gap is normal between guides, so don’t treat any one of them as gospel.
London and the South East
Expect to pay about 15% to 25% more in London and the South East. less.co.uk and BestBuilders both use that range.
less.co.uk’s regional table, for a mid-range insulated office of about 12m² fully installed with base, electrics and heating:
| Region | Average cost | vs national |
|---|---|---|
| London | £22,000 | +25% |
| South East | £20,000 | +14% |
| Midlands | £17,500 | Average |
| North West | £16,500 | -6% |
| Scotland | £16,000 | -9% |
| Wales | £15,500 | -11% |
| North East | £15,000 | -14% |
The same page says the building itself costs about the same everywhere. What changes is groundworks, installation labour and the electrical connection. Note its own South East figure (+14%) sits below the 15% to 25% it quotes in the text.
What owners actually report paying
Owners and buyers on forums report anything from about £4,000 to £34,000 for rooms of similar size. The difference is almost always DIY versus turnkey, and whether insulation, base and electrics were included. These figures come from forum posts, are mostly 2021 to 2025 prices (one is from 2018), and haven’t been adjusted for inflation.
| Size | How it was built | Reported cost | Where |
|---|---|---|---|
| 4m x 3m | Installed by a company, insulated, double glazed | £12,000 building, plus about £1,000 base and £700 electrics | Mumsnet, 2023 |
| About 2.4m x 3m (8x10ft), SW London | Bought building, with clearance and base and the electrics priced separately | £14,000 building, about £1,000 base, about £2,000 electrics | Mumsnet, 2023 |
| 3m x 5m, London | Contractor, everything in; the cheaper of two quotes, about to be installed | £34,000 all in | Mumsnet, 2023 |
| 3m x 5m | Company built, fully insulated | £30,000 | Mumsnet, 2023 |
| About 4.5m x 3m | DIY build, professional electrician | “About 7k all in” for clearance, foundations and materials; the electrician’s part was £780 | Mumsnet, 2023 |
| About 5m x 3.5m | Self-built, insulated, heated | “A shade over 10 grand”; the owner estimated “about 25-30 grand” from a garden room company | Mumsnet, 2025 |
| Not stated | Not stated | “About £20K” in 2021; doesn’t say whether the base and electrics were included | Mumsnet, 2025 |
| 3.6m x 4.8m external | Self-built in 2018 | Just over £12,000, excluding the base | BuildHub, 2026 |
The pattern is clear. Self-builders with a paid electrician report totals of roughly a third of the turnkey prices they were quoted or expected. Turnkey prices in London run highest.
How to compare garden room quotes
Line quotes up on internal floor area, spec and exclusions, not on the headline figure. Two quotes for “a 4m x 3m room” can differ by £10,000 and both be fair.
Ask each installer for the same things in writing:
- Internal floor area and height. Building regulations measure floor area to the finished internal faces of the walls (legislation.gov.uk, regulation 2). A room sold by its outside size can have much less space inside.
- The wall, roof and floor build-up. Ask for insulation type and thickness for each, plus glazing type.
- The base. Which type, who digs it, and what happens if the ground turns out to be clay or sloped.
- The electrics. Is the cable run from the house included, and how many metres? Is there a consumer unit? Who issues the Part P certificate?
- Every exclusion. Delivery, site clearance, skips, guttering, decoration, flooring, heating.
- VAT. Shown separately, or stated as included.
- Payment schedule. How much up front, how much before installation, and how it’s protected.
Then add your own 10% to 15% contingency to whichever quote you pick.
FAQ
Is £6,000 realistic for a garden room?
Not for an insulated, installed room you can use all year. £6,000 buys an uninsulated summerhouse or a basic kit you build yourself. A Mumsnet poster who saw 17x10ft rooms at “around £6k” was told to budget “much more than £6K” by an owner who paid about £20,000 in 2021 (Mumsnet, 2025).
Is a garden room cheaper than an extension?
Usually, yes. less.co.uk puts a 12m² garden room at £10,000 to £24,000 against £25,000 to £50,000 or more for a single-storey extension of the same floor area. MyBuilder and BestBuilders both put extensions at £2,000 to £3,000 per m².
Do you pay VAT on a garden room?
Yes, at 20% in almost every case. New construction is normally standard-rated, and a garden room or annexe used with the main house doesn’t qualify for zero-rating (HMRC VAT Notice 708). Check whether a quote includes it, as several price guides don’t say.
Does a bigger garden room need building regulations approval?
Past 30m², yes. In England and Wales a detached building of 15m² or less with no sleeping accommodation is exempt from most building regulations. Between 15m² and 30m² it must be at least 1m from every boundary or built substantially of non-combustible material. Over 30m², or with anyone sleeping in it, you need approval (legislation.gov.uk). Electrics are notifiable at any size.
How long does a garden room take?
Expect about 12 weeks from order to installation for most companies (The Garden Room Guide). The build on site is much quicker. Gardensite says installation of the Forest Xtend typically follows two to four weeks after delivery, and delivery itself takes six to ten weeks.
What to do next
- Measure the spot and decide the internal floor area you need. Staying at 15m² or under keeps building regulations simple.
- Pick a spec level and multiply it out: £1,500 to £2,000 per m² for a standard insulated room is a sensible starting point.
- Get at least three written quotes and fill in the comparison list above for each one.
- Price the base and the cable run separately if any quote leaves them out.
- Add 10% to 15% contingency, and don’t pay a large deposit until you know how it’s protected.
Sources
- less.co.uk: Garden room cost UK 2026 (April 2026)
- BestBuilders: Garden room cost UK (updated 7 September 2026)
- MyBuilder: Garden room cost (updated 21 August 2026)
- MyJobQuote: Garden room cost (updated 6 October 2026)
- The Garden Room Guide: Garden room prices (14 June 2026)
- The Garden Room Guide: Setting a budget for your garden room (January 2026)
- Homebuilding & Renovating: Garden room cost (June 2023)
- Gardensite: Forest Xtend 4.0 garden office
- legislation.gov.uk: Building Regulations 2010, Schedule 2
- legislation.gov.uk: Building Regulations 2010, regulation 2 (floor area)
- Planning Portal: Exemptions from building regulations
- Planning Portal: Outbuildings planning permission
- GOV.UK: Fees for planning applications in England from 1 April 2026
- HMRC: VAT Notice 708, buildings and construction
- Homebuilding & Renovating: Approved Document P
- Mumsnet: Cost of putting in a garden office (2023)
- Mumsnet: Is a garden room worth it? (2025)
- Mumsnet: Garden office (2025)
- BuildHub: Our garden room self-build