The short answer
A supplied-and-fitted garden room typically costs £2,000–£3,500 per square metre in 2026. So a 10m² room (around 4 × 2.5m) usually lands somewhere between £20,000 and £35,000, and a 15m² room (around 5 × 3m) between £30,000 and £52,500. The rate is a useful sanity check, but it is not fixed — small rooms cost more per m² than large ones, and glazing, groundworks and finish move the figure either way. Treat it as a benchmark, not a quote. See the main cost guide for the full price picture.
Cost per square metre is the quickest way to compare garden room quotes that come in different sizes, because it strips out the effect of footprint and leaves you comparing specification. But it is widely misunderstood: people see a low headline rate and assume it is the better deal, when in fact a cheaper rate often means a thinner build — less insulation, single glazing, a shed-grade roof. This guide explains what the rate covers, why small rooms cost more per m², and how to use the number to catch an underspecified or overpriced quote.
Per-square-metre costs at a glance
- Typical rate £2,000–£3,500/m²
- Budget / kit end From ~£1,500/m²
- Premium / high glazing £3,500–£5,000/m²+
- 10m² room ~£20,000–£35,000
- 15m² room ~£30,000–£52,500
- Small rooms Higher rate per m²
Why small rooms cost more per square metre
Fixed costs do not shrink with the room. The base, the delivery, the electrical connection back to the house, the door set and a chunk of the labour cost broadly the same whether the room is 8m² or 18m². Spread across fewer square metres, those fixed costs push the rate up. That is why a tiny 6m² office can come in at £3,500/m² while a 20m² studio of the same specification works out closer to £2,200/m². When you compare two quotes on rate alone, make sure they are a similar size — otherwise you are comparing the maths, not the build.
| Floor area | Approx. size | At £2,500/m² | At £3,200/m² |
|---|---|---|---|
| 7.5m² | 3 × 2.5m | £18,750 | £24,000 |
| 10m² | 4 × 2.5m | £25,000 | £32,000 |
| 15m² | 5 × 3m | £37,500 | £48,000 |
| 20m² | 5 × 4m | £50,000 | £64,000 |
What the rate should include
A genuine supplied-and-fitted rate covers the base or foundation, the insulated timber frame, full insulation to floor, walls and roof, double glazing, exterior cladding, a weatherproof roof, internal finishes and a basic electrical fit-out certified under Building Regulations Part P. If a quote shows a low rate, find out what has been left out: groundworks, the electrical connection, glazing upgrades and VAT are the usual exclusions. A £1,800/m² quote that excludes the base and electrics is not cheaper than a £2,600/m² quote that includes them — it is simply less complete. Always compare like for like on insulation and glazing.
What pushes the rate up
Lots of glazing is the single biggest driver — a wall of bi-fold or sliding doors can add thousands. A higher insulation specification, underfloor heating, a green or premium roof, bespoke joinery and a tricky site (slope, poor access, soft ground for the foundations) all push the rate up. At the other end, a kit or self-build can drop the headline rate sharply — but only because you are taking on the base, insulation and electrics yourself, so the labour and risk move to you rather than disappearing. This is general information; your actual rate depends on your garden, ground conditions and the quotes you receive.
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Frequently asked questions
How much is a garden room per square metre in 2026?
Typically £2,000–£3,500 per square metre supplied and fitted. Budget kit builds can start nearer £1,500/m², while premium rooms with lots of glazing can exceed £3,500–£5,000/m². Smaller rooms cost more per m² than larger ones.
Why is a small garden room more expensive per m²?
Because fixed costs — the base, delivery, electrical connection and door set — do not shrink with the room. Spread across fewer square metres, they raise the rate. A 6m² room can cost £3,500/m² while a 20m² room of the same spec works out nearer £2,200/m².
Does the per-m² rate include groundworks and electrics?
It should, but not always — a low rate often excludes the base, the electrical connection, glazing upgrades or VAT. Always check what a rate covers before comparing it. A complete higher rate can be cheaper overall than a low rate with exclusions.
Is a lower cost per m² always better value?
No. A low rate often means a thinner build — less insulation, single glazing, a lighter roof — or major exclusions. Use the rate to flag outliers, then read the specification to see what you are actually getting.
Sources & further reading
- Trade and industry pricing guidance — typical garden room cost-per-m² ranges
- GOV.UK / Building Regulations Approved Documents L and P — energy efficiency and electrical safety
- GOV.UK Planning Portal — outbuildings and permitted development
This is general information, not advice for your specific property or project. Costs vary with size, specification, ground conditions and the quotes you receive — confirm planning with your Local Planning Authority.