Can You Sign Off the Ground Conditions and Foundations?

This is one of the most common questions we receive, and the short answer is: we design to the information available, but ground conditions are confirmed on site by Building Control — not by us remotely.

What PorthouseDean Does

We produce structural calculations for foundations based on the information you provide: your architectural drawings, the proposed loads, the location of the site and any soil or tree survey data available. We design the foundation to an assumed bearing capacity (typically 100 kN/m² for most residential ground conditions unless you tell us otherwise) and specify the required depth, width and concrete specification.

If you have a ground investigation report — a soil survey — we use that data to refine our design. If you do not, we work to conservative defaults and flag where ground conditions need to be confirmed.

What Building Control Does

The Building Control Officer (BCO) is the party who physically inspects the foundation trench on site and confirms whether the formation level soil looks acceptable. This is a legal requirement under the Building Regulations and cannot be substituted by desk-based engineering calculations.

When your builder reaches formation level during excavation, they must call for a BCO inspection before pouring concrete. The BCO will look at the soil, confirm it looks consistent with the design assumptions, and give the go-ahead — or ask for deeper excavation if the ground is soft or variable.

When Ground Surveys Are Needed

A formal ground investigation is not always required, but it becomes important when:

– There are trees within 20 metres (particularly on clay soil, where tree roots cause seasonal shrinkage and heave)
– The site has a history of made ground, fill or mining activity
– Visual signs of subsidence or settlement are present
– The BCO specifically requests geotechnical data

In those cases, a geotechnical engineer should be commissioned to carry out trial pits or borehole tests and produce a report. PorthouseDean can then use that report to produce more accurate foundation specifications.

What This Means for Your Project

Do not expect your structural engineer to sign off that the ground is adequate — that sign-off comes from the BCO on site inspection. What your engineer provides is a calculation showing that the foundation design is appropriate given acceptable ground conditions, and the BCO’s job is to confirm those conditions exist.

If you are unsure what investigation your project needs, get in touch with PorthouseDean at the start of the design process so we can advise before work begins.