Concrete pad foundations + bearers under a garden room
Priced on our reference 4 m × 3 m insulated office: the base stage costs £788 in materials, of a £10,320 whole-build materials total.
£788base-stage materials
£10,320whole build, ex VAT
£1,132/m²per internal m²
What is in the base stage
| Item | Spec | Cost |
|---|---|---|
| Treated bearers 100×150 | 4 runs × 3.90 m | £98 |
| Concrete pad foundations | 4 runs × 4 pads – 200×200 mm, 300 mm deep | £512 |
| Bagged concrete (pads) | ≈0.19 m³ mixed + 10% – general foundation mix | £110 |
| Cast-in bolts + nuts/washers | M12, one per pad, set in the wet concrete | £56 |
| Damp-proof membrane (DPM) / ground barrier | 1200-gauge polythene, footprint | £12 |
When to choose it
For: Cheapest materials, simple hand-dig holes, good on firm level ground.
Against: Slowest DIY route (setting out + curing per pad), less tolerant of soft ground.
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.