The short answer
A garden room typically costs £10,000–£30,000 supplied and fitted in 2026. A compact insulated office of around 3 × 2.5m starts at roughly £8,000–£15,000; a large or luxury room can reach £30,000–£50,000 or more. As a rule of thumb, expect about £2,000–£3,500 per square metre supplied and fitted. Size, glazing, insulation specification, the base type and groundworks are the main variables. See our cost per square metre guide to sanity-check any quote. These are typical figures, not quotes.
A garden room is one of the larger discretionary purchases a UK household makes, and the prices advertised online — from a few thousand pounds for a self-assembly kit to over fifty thousand for an architect-designed studio — can make it hard to know what is reasonable. This guide sets out realistic 2026 supplied-and-fitted ranges by size and specification, explains what drives the differences, and flags the scenarios that push costs up so there are no surprises in a quote.
Garden room costs at a glance
- Compact office (approx. 3 × 2.5m) £8,000–£15,000
- Mid-size room (approx. 4 × 3m) £15,000–£25,000
- Large room (approx. 5 × 4m) £25,000–£35,000
- Large / luxury / studio £30,000–£50,000+
- Per square metre (supplied & fitted) £2,000–£3,500/m²
- Self-build kit (supply only) From £5,000–£15,000
Supplied-and-fitted costs by size
For most buyers, a fully insulated, supplied-and-fitted garden room is the benchmark to price against, because it includes the base, the structure, insulation, glazing, electrics and a finished interior. A compact home office of around 3 × 2.5m (roughly 7.5m²) typically costs £8,000–£15,000 depending on glazing and finish. A mid-size room of around 4 × 3m (12m²) commonly lands at £15,000–£25,000, and a large 5 × 4m room (20m²) at £25,000–£35,000. Premium studios with extensive glazing, high insulation values, bespoke cladding or integrated bathrooms can exceed £50,000. Location matters too: London and the South-East typically run 10–20% above the national average. For a like-for-like sanity check across sizes, the per-square-metre figure is the most useful single number — see our cost per square metre guide.
| Size (approx.) | Floor area | Supplied & fitted (typical) |
|---|---|---|
| Compact (3 × 2.5m) | ~7.5m² | £8,000–£15,000 |
| Mid-size (4 × 3m) | ~12m² | £15,000–£25,000 |
| Large (5 × 4m) | ~20m² | £25,000–£35,000 |
| Luxury / studio | 20m²+ | £30,000–£50,000+ |
What is included in a supplied-and-fitted price
A proper supplied-and-fitted quote should cover the foundations or base, the timber frame, full insulation to the floor, walls and roof, double-glazed doors and windows, exterior cladding, a weatherproof roof covering, internal wall and floor finishes, and a basic electrical fit-out connected back to your home consumer unit. What separates a usable, year-round garden room from a glorified shed is the specification underneath the surface — the insulation and glazing in particular. See our insulation guide for what to look for, and the build process guide for how it all goes together. A typical garden office aimed at year-round use will also be quoted as a turnkey item; our garden office cost guide breaks that down.
What pushes costs up
Several factors can push a garden room above the typical ranges:
- Glazing — large bi-fold or sliding doors and extensive windows add significantly to cost compared with a single door and modest windows.
- Groundworks and access — sloping ground, poor access for materials, or the need for an engineered base raises the foundation cost. See our foundations and base guide.
- Plumbing for a toilet or kitchenette — adding water and drainage means Building Regulations work and can affect your planning position. See whether you can put a toilet in a garden room.
- Higher insulation and heating — upgrading insulation values, adding underfloor heating or air conditioning increases both build and running costs.
- Distance for electrics — a long armoured-cable run from the house consumer unit adds material and labour. See our electrics and Wi-Fi guide.
Planning, Building Regulations and cost
Most garden rooms are built as permitted development, which avoids the time and cost of a full planning application. But the moment a room becomes self-contained living or sleeping accommodation — a “granny annexe” — it generally needs full planning permission and Building Regulations approval, both of which add cost and time. Building Regulations are also triggered by floor area: broadly, a room under 15m² with no sleeping accommodation usually does not need approval, and one under 30m² may be exempt subject to conditions (no sleeping use, and either at least 1m from a boundary or built of non-combustible materials). Sleeping accommodation always needs Building Regulations. These are general points — rules vary locally and can be removed by an Article 4 direction, so always confirm with your Local Planning Authority. See our planning permission guide.
DIY versus supplied and fitted
A self-build or kit garden room can reduce the headline cost — supply-only kits start from around £5,000 for a basic insulated shell — but you take on the base, electrics, insulation detailing and weatherproofing yourself, and any mistakes are expensive to put right. For most people, a supplied-and-fitted room from an established builder gives a better outcome and a clearer warranty. Our DIY versus supplied-and-fitted guide sets out the real trade-offs. This is general information; costs vary with your specific garden, ground conditions and the quotes you receive, and any electrical or drainage work must comply with the relevant Building Regulations.
Compare garden room quotes
Prices vary significantly between builders for the same size and specification. Use our service to compare quotes from garden room builders in your area.
Frequently asked questions
What is the average cost of a garden room in the UK?
A typical insulated, supplied-and-fitted garden room costs £10,000–£30,000 in 2026. A compact office of around 3 × 2.5m starts at roughly £8,000–£15,000, while large or luxury rooms can reach £30,000–£50,000 or more. The range reflects size, glazing, insulation specification, base type and location.
How much is a garden room per square metre?
As a benchmark, expect roughly £2,000–£3,500 per square metre supplied and fitted for an insulated, year-round garden room. Smaller rooms tend toward the higher end per square metre because fixed costs like the base and electrics are spread over a smaller area.
Is a garden room cheaper than an extension?
Often, yes. A garden room avoids structural work to the house and frequently falls under permitted development, whereas an extension usually needs planning permission and Building Regulations. However, a garden room is detached and counts differently toward home value — see our garden room versus extension guide for the full comparison.
Can I get a cheaper garden room as a self-build kit?
Self-build kits start from around £5,000 supply-only, but you take on the base, insulation, electrics and weatherproofing yourself. For most buyers a supplied-and-fitted room from an established builder produces a better, warrantied result. See our DIY versus supplied-and-fitted guide.
Sources & further reading
- GOV.UK Planning Portal — outbuildings, permitted development and when planning permission is needed
- GOV.UK / Building Regulations Approved Documents (Part L, Part H, Part P) — energy efficiency, drainage and electrical safety
- Your Local Planning Authority — local rules, conservation areas, Article 4 directions and confirmation for your property
- Trade and industry pricing guidance — typical supplied-and-fitted garden room cost ranges
This is general information, not advice for your specific property or project. Costs, timescales and outcomes vary with your garden, ground conditions and chosen builder. Planning rules vary locally and permitted development can be removed by an Article 4 direction — always confirm with your Local Planning Authority.