Guide
Site investigation report: what it contains and who relies on it
Updated
The report is the product. The holes are temporary; what your engineer, building control and warranty provider rely on is the document, so it pays to know what a complete one contains before comparing fees.
What a complete report contains
- The ground model: exploratory hole logs (pits, windows or boreholes), strata descriptions, and groundwater observations.
- Laboratory results: soil classification, strength, sulfate/concrete design class, and chemical suites where contamination was in scope.
- Interpretation (in an interpretative report): foundation recommendations, bearing capacity commentary, and flags such as shrinkable clay near trees or obstructions in made ground.
- Compliance framing: work planned and reported under BS 5930 and Eurocode 7, so third parties can rely on it without re-investigation.
Factual vs interpretative
A factual report records what was found and costs less; an interpretative report adds engineering conclusions and recommendations. If a structural engineer is already appointed, they may only need factual data, since interpretation is their job. If no engineer is appointed yet, the interpretative report is usually worth its premium, because it is the document building control and warranty providers can act on directly. The report is normally included in the quoted investigation fee, so the real comparison between quotes is scope, not a separate report price.
Reading a quote like a professional
- Check the number, type and depth of exploratory holes against what your engineer asked for, like for like.
- Check the lab testing schedule is itemised: classification, sulfate and any chemical suites named, not "testing as required".
- Check the deliverable: factual or interpretative, and whether the firm carries professional indemnity insurance for the advice given.
This site explains fees and process; it is not engineering advice, and nothing here replaces a structural engineer's specification for your site. Get quotes from ground investigation firms and let them price the scope your project actually needs.