Foundation excavation inspection report
An inspection of foundation excavations before concrete is poured, to confirm the ground and dimensions match the design.
About this service
Once concrete is poured into a foundation trench, nobody can check what it is sitting on. That makes the gap between digging and pouring critical. Our inspection confirms that the trench has reached a suitable bearing stratum, that its depth and width match the design, and that nothing on site, such as a root, an old drain or a pocket of soft fill, undermines the assumptions the foundation was designed on.
Building Control officers often inspect foundations themselves, but they may ask for an engineer's report where the design depends on a specific stratum or depth, where trees are nearby, or where the ground has turned out differently from what was expected. Builders also call us when they hit something unexpected and need a decision quickly, so the trench does not sit open and soften in the rain.
On London Clay, the key checks are depth relative to nearby trees, signs of desiccation and roots below the base. On gravels and made ground, the question is whether the trench has passed through loose fill onto firm natural soil. Our guide to clay, trees and foundations explains why. Every report is signed off by a chartered engineer who is a Member of the Institution of Civil Engineers (MICE).
When you need it
- Building Control or your design requires an engineer to inspect foundations
- Ground conditions on site look different from expected
- You want assurance before pouring concrete
What's included
- Inspection of the excavations
- Check of depth, width and bearing stratum
- Advice on any changes needed
How it works
- Book before the pourContact us when the excavation is nearly complete, ideally a day or two ahead. We need the foundation drawings and calculations, plus the ground investigation if one was carried out.
- Inspect the trenchesOn site we measure depth and width at intervals, examine the base and sides, and test the soil by hand. We look for roots, soft spots, water, and services or old foundations crossing the line.
- Decide on siteIf the ground is acceptable we confirm it there and then so the builder can pour. If not, we explain how much deeper to dig or whether a different foundation solution is needed.
- Issue the reportA short report with photographs, measurements and conclusions follows, ready for Building Control. Where changes were made on site, the report records them so the as-built foundation is documented.
What you receive
What happens if the ground is not what was expected?
Surprises are common in London back gardens. Footings from demolished outbuildings, backfilled ponds, buried rubble and roots from a neighbour's tree can all appear in a trench that looked straightforward on paper. Most can be dealt with by digging deeper to firm natural ground and filling with mass concrete. Where the depth becomes excessive, a different approach set out in a revised foundation design may be more economical.
If water floods the trench or the base turns soft, the builder should not pour until loose material is removed and the base is checked again. Pouring over mud or standing water is one of the commonest causes of later settlement. If digging exposes cracking or shallow footings to the existing house, flag it straight away so the junction can be reviewed before new concrete is cast against it.
Frequently asked questions
Does Building Control need to inspect foundations before concrete is poured?
Yes, foundation excavations are one of the standard stages your builder must notify to Building Control before pouring. Some officers attend in person, while others accept an engineer's inspection report, particularly on difficult ground or where the design relies on a specific depth. Confirm the arrangement with your officer at the start so the right inspection is booked.
How deep should foundations be near trees?
It depends on the tree species, its mature height, its distance from the foundation and how shrinkable the clay is. Industry guidance sets deeper minimum depths the closer and thirstier the tree, and Building Control will confirm what they accept. Where a tree is close, our tree influence assessment establishes the required depth before digging begins.
How quickly can an engineer inspect a foundation?
Give us as much notice as possible, ideally while the excavation is still under way rather than once it is finished. Trenches left open in wet weather deteriorate quickly and may need cleaning out again before they can be inspected and poured, which costs the builder time and adds to the risk of a soft base.
What does a foundation inspection cost?
Our foundation excavation inspection report starts from £250 + VAT for a single visit. Larger sites, several visits or significant changes that need redesign cost more. We confirm a fixed fee in writing before attending, so the builder can plan the pour knowing the inspection is already arranged and paid for.