It is the first question almost everybody asks, and the honest answer is that it depends on the site. That is not a dodge — below is exactly what it depends on, so you can judge whether a quote you have been given is reasonable.
What actually drives the price
Four things move the number more than anything else.
- How many trial pits the design needs. This is the biggest single factor. A small extension may need one or two; a larger site or a scheme with several soakaways will need more. Each pit has to be dug, then filled and timed three times over.
- Whether you need one test or two. Surface water testing to BRE 365 and foul testing to BS 6297 are separate tests with separate results. Rural sites with no mains foul connection often need both. Doing them on one visit is far cheaper than two.
- Access. If a machine can get to the test location, the work is straightforward. If it cannot — a walled back garden, a steep plot, no gate wide enough — the pits may have to be dug by hand, and that takes considerably longer.
- Distance. Most firms build travel into the price. A site twenty minutes away costs less to attend than one three hours away.
Why quotes vary so much
If you gather three quotes you will often see a wide spread, and the cheapest is not always doing the same job. The most common reason for a low price is a test that cuts corners — a single trial pit where the design needs several, or one filling instead of three.
BRE Digest 365 asks for each pit to be filled and timed on three separate occasions, with the slowest of the three results used for the calculation. A single filling is quicker and cheaper, and it is the sort of thing that gets picked up when the drainage design is reviewed. A retest costs more than getting it right first time.
Questions worth asking before you accept a quote
- How many trial pits is that price for?
- Does it include three timed fills per pit, as BRE 365 requires?
- Is a written report included, with the recorded times, or just a single figure?
- Does the price cover surface water only, or foul as well?
- What happens if the ground fails — is there a charge for a report that says infiltration is not viable?
That last one matters more than people expect. A failed test is not a wasted test: it is the evidence your engineer needs to justify a different drainage approach, and it is what a water authority will want to see under a Section 106 application before accepting a surface water connection. It should still come with a proper report.
What we do
We quote per site rather than off a price list, because the honest number depends on the four things above. Send us the postcode and roughly what is proposed — extension, self build, barn conversion, a full development — and we will come back with a fee proposal. Allow up to 48 hours. There is no charge for the quote, and if we think you need a different test from the one you have asked for, we will tell you before you commit.
We own our own machinery rather than sub-contracting the digging, which keeps our overheads down, and we are based in Wolverhampton, so sites across the Midlands and the Welsh borders carry very little travel.