Ground screws under a garden room
Priced on our reference 4 m × 3 m insulated office: the base stage costs £588 in materials, of a £10,119 whole-build materials total.
£588base-stage materials
£10,119whole build, ex VAT
£1,110/m²per internal m²
What is in the base stage
| Item | Spec | Cost |
|---|---|---|
| Ground screws | 4 runs × 4 posts | £512 |
| Screw-head bolts / brackets | M10, one set per screw – often supplied with the screws; confirm | £64 |
| Damp-proof membrane (DPM) / ground barrier | 1200-gauge polythene, footprint | £12 |
When to choose it
For: No dig, no spoil, installed in a morning, works on slopes, removable.
Against: Per-screw cost adds up on big footprints; needs a torque-certified installer for warranty.
Compared with the alternatives (same 4×3 build)
| Base | Base stage | Whole build |
|---|---|---|
| Ground screws | £588 | £10,119 |
| Concrete slab | £428 | £9,313 |
| Concrete pad foundations + bearers | £788 | £10,320 |
Twenty Paces is a planning aid, not professional structural or planning advice. Costs are materials-only at indicative merchant rates (excluding labour and delivery); span tables, U-values and regulations thresholds are indicative. Verify your design with a structural engineer, your local planning authority and Building Control before you build.