Guide
Ground investigation cost: what a GI actually costs in 2026
Updated
A ground investigation (GI) is professional time plus plant plus laboratory testing, so the fee moves with scope. Here is what typical 2026 quotes look like for domestic-scale work, and the choices that move them.
Typical fees at a glance
| Scope | Typical fee |
|---|---|
| Phase 1 desk study only | £500–£1,200 |
| Phase 2, trial pits or window sampling, single plot | £1,500–£4,000 (lower half of the range) |
| Phase 2 with borehole rig, single plot | £1,500–£4,000 (upper half, and above for deep or difficult work) |
| Development sites, multiple plots | Scoped and priced per scheme |
These are typical market quote ranges, not fixed fees. What you are buying is the information your structural engineer needs to design foundations that suit the actual ground, which is why the sensible order is: engineer names the questions, the GI answers them, the foundation design follows. A GI scoped without knowing the questions tends to cost more and answer less.
What moves the fee
- Method: machine-dug trial pits are cheaper than boreholes; a tracked rig, deeper holes and in-situ testing push the fee up. See boreholes or trial pits.
- Access: a rear garden with no side access, live services or protected trees can add mobilisation and reinstatement cost.
- Laboratory testing: soil classification, chemical (contamination) suites and concrete design (sulfate) suites are itemised; more suites, higher fee.
- Reporting: a factual report states what was found; an interpretative report adds engineering recommendations and costs more. See what's in the report.
Why the money is well spent
Foundation design is the single largest unknown in most self-build budgets. Where the ground is suspect (shrinkable clay with trees nearby, made ground, slopes, former industrial use), building control bodies and structural warranty providers such as NHBC commonly require ground investigation evidence before foundations are approved; that is standard practice on suspect ground rather than a blanket legal rule. The governing standards for how investigations are planned and reported are BS 5930 and Eurocode 7; a competent firm will reference both without being asked.
Contaminated land assessments follow the phased approach in the Environment Agency's land contamination guidance (gov.uk): desk study first, intrusive work only where the desk study justifies it. Doing phase 1 first is usually the cheapest way to spend less on phase 2.