Garden Room Cost Calculator
Detached, usually no planning permission, and no disruption to the house. Priced per square metre by how well it is insulated — which decides whether you can use it in January.
Open the calculator →Price a garden room in 30 seconds
4 steps. Covers floor area, insulation spec, foundations and region.
How this calculator works
Garden rooms are priced per square metre, and the spec band you choose matters more than anything else — it is the difference between a summerhouse you use from April to September and a room you work in through the winter. The gap between basic and standard insulation is roughly £500/m², and it is the one place not to economise if the room has a job to do.
Foundations are priced per square metre too, since they scale with footprint. Ground screws are the usual choice: quick, no spoil, and no concrete lorry needed down a side alley. A slab is more robust but needs access.
On permissions: a garden room is normally permitted development as an outbuilding — single storey, under 2.5m high within 2m of a boundary, and not forward of the principal elevation. Building regulations generally do not apply under 30m² if it is at least 1m from any boundary and contains no sleeping accommodation.
Garden room costs by specification (2026)
| Specification | Typical 2026 cost | Notes |
|---|---|---|
| Basic / summerhouse | £1,000–£1,400/m² | Spring to autumn use |
| Standard insulated | £1,500–£2,000/m² | Usable year-round |
| High-spec | £2,000–£2,500/m² | Heating and proper electrics |
| Premium / bespoke | £2,500–£3,500/m² | Architect-designed |
| Ground screws | £30–£50/m² | Quickest foundation |
| Screw piles | £50–£80/m² | Poorer ground |
| Concrete slab | £80–£120/m² | Most robust |
| Flat-pack / kit | £6,000–£15,000 | Self-build, excludes base and power |
Rates match our garden room cost guide. Plumbing and drainage are excluded — adding a WC or kitchenette changes both the cost and the regulations position.
Garden room calculator FAQs
Usually not. As an outbuilding it is normally permitted development if it is single storey, no more than 2.5m high where it sits within 2m of a boundary, not forward of the principal elevation, and covers no more than half the garden. Listed buildings and some conservation areas are excluded.
Generally not under 30m² floor area, provided it is at least 1m from any boundary and contains no sleeping accommodation. Go over 30m², move it closer to a boundary, or add a bedroom, and the regulations apply — as they do to the electrical installation regardless, under Part P.
If it is an office you will use through the winter, standard insulated as a minimum — the basic band is a summerhouse and will be cold and prone to condensation from November. The extra roughly £500/m² is what makes it a room rather than a shed.
A well-built insulated one usually does, though rarely pound for pound, and valuers treat it as ancillary space rather than as floor area. A cheap uninsulated cabin adds little and can read as clutter. Build it properly or do not build it.
Related cost guides
- Garden room cost guide — full 2026 pricing by spec
- Garden room planning rules — the outbuilding allowance
- Garage conversion calculator — a cheaper route to a room
- House extension costs — extending the house instead
Get My 3 Free Garden Room Quotes
60 seconds · No spam · No obligation