Guide
Boreholes or trial pits: choosing the cheaper right answer
Updated
The method is the biggest single price lever in a phase 2 investigation. The cheap method is fine surprisingly often, and wrong expensively when it is wrong, so the choice belongs to your engineer, not to the price list.
The methods, plainly
- Trial pits
- Machine-dug pits, typically a few metres deep, logged by an engineer on site and backfilled the same day. The cheapest way to see the ground, foundation depths of neighbouring structures, roots and groundwater near the surface. Sits at the lower end of the £1,500–£4,000 single-plot range (typical 2026 quotes).
- Window sampling
- A small percussive rig taking continuous soil samples from a narrow hole. Deeper than a pit, lighter and cheaper than a full borehole rig, and often the right middle answer for house plots with restricted access.
- Boreholes
- A drilling rig forming deeper holes with in-situ testing (such as standard penetration tests) and sampling for the lab. The most expensive method per hole and the only honest one where deep information is needed: basements, piled foundations, deep made ground, contamination at depth.
How the choice is made
- Start from the structure. A two-storey house on strip footings asks shallow questions; pits or window samples usually answer them.
- Let the desk study steer. Deep fill, buried structures or contamination flagged at phase 1 push the method towards boreholes before anyone mobilises.
- Price the whole job, not the hole. We deliberately do not quote per-borehole or per-metre rates: they vary too much with rig type, depth, access and testing to compare honestly. Compare complete scoped quotes instead.
Whichever method is used, the work should be planned and reported to BS 5930 and Eurocode 7, and the samples that matter should go to the laboratory: the drilling is only as valuable as the testing and interpretation attached to it. Get scoped quotes for your plot from firms that carry both options.