Garden Office Cost Calculator
Estimate what your garden office or garden room will cost in 2026. Pick a size, add the extras you want and enter your postcode — the calculator builds a fully-installed range including foundations and VAT.
Size
Extras
Used for a regional cost adjustment — London and the South East run higher.
£21,600 – £36,000
Fully installed, including foundations and VAT.
- Base build
- £16,000 – £26,000
- Foundations & groundworks
- £2,000 – £4,000
- VAT (20%)
- £3,600 – £6,000
The electrical supply run from the house consumer unit (£400–£1,500) is usually quoted separately.
An indicative estimate — your final quote depends on site access, spec and finish.
Garden office cost by size (2026)
All figures are fully installed, including foundations and VAT, for a mid-spec build. Per-m² rates are highest on compact builds because fixed costs spread over fewer square metres.
| Size | Floor area | Installed cost | Cost / m² |
|---|---|---|---|
| Small | 6–8m² | £15,000 – £25,200 | £2,150–£3,600/m² |
| Medium | 10–15m² | £21,600 – £36,000 | £1,800–£3,000/m² |
| Large | 16–25m² | £30,600 – £49,200 | £1,550–£2,450/m² |
| Extra Large | 25m²+ | £44,400 – £69,600 | £1,400–£2,200/m² |
Add-ons & upgrades
Typical costs for the extras buyers ask about most. Electrics (lights, sockets and data) are part of every base build.
| Extra | Typical added cost |
|---|---|
| Underfloor Heating | +£800 – £2,500 |
| Kitchenette / Plumbing | +£2,000 – £4,500 |
| Bathroom / Shower Room | +£4,000 – £10,000 |
| Premium Cladding (cedar / larch) | +£1,500 – £3,500 |
| Bi-fold / Sliding Doors | +£1,500 – £6,000 |
| Planning Support | +£500 – £1,200 |
| Electrics & Data Cabling | Included in base build |
How the calculator works
Each estimate is built from the same formula:
total = (base build + foundations + extras) × regional uplift × (1 + VAT)
- Base build — structure, cladding, insulation, double glazing, electrics, interior finish and delivery & install.
- Foundations & groundworks — shown separately, as they vary with your footprint and site.
- Regional uplift — +20% for London, +10% for the wider South East.
- VAT — added at 20%.
- Quoted separately — the electrical supply run from the house consumer unit (£400–£1,500).
FAQs
How accurate is this garden office cost calculator?
It gives an indicative range based on 2026 UK prices for a professionally installed, mid-spec timber-frame or SIPs build. Your final quote depends on site access, ground conditions, spec and finish, so treat it as a starting point before getting installer quotes.
Does the estimate include VAT and foundations?
Yes. Both foundations & groundworks and VAT (20%) are shown as explicit line items in the total. The one cost usually quoted separately is the electrical supply run from the house consumer unit (£400–£1,500).
Why do smaller garden offices cost more per m²?
Fixed costs — doors, glazing, electrics, delivery and install mobilisation — are spread over fewer square metres, so the rate per m² is highest on compact builds and falls as the footprint grows.
Does my location change the price?
Yes. Labour and delivery cost more in and around the capital, so the calculator adds a regional uplift of +20% for London postcodes and +10% across the wider South East.