3.6m × 3m garden room: what it really costs to build
Every figure below is computed by the same parametric engine that produces our buildable plans - a full insulated timber-frame spec (150 mm floor, 125 mm walls, 100 mm warm roof, EPDM), priced line-by-line at indicative UK merchant rates.
Cost by build stage
| Stage | Materials |
|---|---|
| Stage 1 – Site base | £443 |
| Stage 2 – Floor | £861 |
| Stage 3 – Wall frames | £1,096 |
| Stage 4 – Roof structure | £1,022 |
| Stage 5 – Sheathing / racking | £200 |
| Stage 6 – Breather membrane | £100 |
| Stage 7 – Windows & doors | £1,650 |
| Stage 8a – Battens + cladding | £1,563 |
| Stage 8b – Roof covering | £1,011 |
| Stage 9 – Insulation + VCL | £530 |
| Stage 10 – First-fix electrics (parts only) | £321 |
| Stage 11 – Plasterboard | £263 |
| Stage 12 – Interior finishes | £423 |
| Total (ex VAT) | £9,483 |
| VAT (20%) | £1,897 |
| Total (inc VAT) | £11,379 |
Add £1,000–£2,000 for electrics + decoration and ~10% contingency: that is where the £13,517–£14,517 budget comes from. A turnkey company would typically quote 2-3× the materials figure once labour and margin are in.
Will it need planning permission?
At a 2.175 m wall height this size clears the headline Permitted Development limits (flat roof, ≥2 m from the boundary):
✓ overall height ✓ eaves height ✓ distance to boundary ✕ other conditions ✓ Building Regs: floor area ✕ Building Control – how it actually works ! Part P – electrical notification ! Structural: roof loading ✕ Structural: roof loading ✕ Structural: roof loading
Spec behind the numbers
| Walls | 47x125 C24 studs @ 400 mm, full-fill insulation, U ≈ 0.19 W/m²K |
| Roof | Warm flat roof, 100 mm PIR over deck, EPDM, U ≈ 0.2 W/m²K |
| Floor | 150 mm insulated joist cassette on ground screws |
| Cladding | Siberian Larch, shiplap, on ventilated battens |
Common questions
How much does a 3.6m × 3m garden room cost to build yourself in the UK?
Materials for a 3.6m × 3m insulated timber-frame garden room come to roughly £9,483 ex VAT (£11,379 inc VAT) at indicative merchant rates - about £1,171 per square metre of internal floor. With electrics, decoration and contingency a realistic all-in DIY budget is £13,517-£14,517. Labour is extra if you are not building it yourself.
Do I need planning permission for a 3.6m × 3m garden room?
Usually not, if it meets Permitted Development rules: single storey, no higher than 2.5 m within 2 m of a boundary (3 m flat-roof overall otherwise), and not forward of the main elevation. At this footprint and a 2.175 m wall height the design checks out against the headline PD limits - verify with your local planning authority.
What internal space does a 3.6m × 3m garden room give?
About 8.1 m² internally (3161 × 2561 mm) once the insulated timber-frame walls are accounted for - comfortable for a one-to-two person office.