Basement impact assessment in Kingston upon Thames

How we build a Kingston upon Thames assessment

The order of work matters. We start with the desk study, because it tells us whether the site sits over clay, gravel or something more awkward, and whether surface water is a known problem. Only then do we brief the ground investigation, so boreholes land where the basement will actually go.

While the investigation runs, we prepare the plans and sections the engineer will design against. When the results arrive, the engineer fixes the retaining wall type and the groundwater measures, and we update the drawings so that the depth on the section matches the depth in the report. A mismatch there is the commonest reason for a request for more information.

We are chartered architectural technologists (MCIAT). We coordinate; the engineer signs. Our structural calculations in Kingston upon Thames page describes how that split works in practice.

Access is the other early question. Boreholes and small rigs have to reach the back garden, sometimes through a side passage or the house itself, and the same constraint later applies to excavators and spoil removal. We note the access route on the plan so the council sees that the outline construction method is realistic.

Constraints specific to Kingston upon Thames

A basement here often sits in a very different setting from inner London. The borough has 28 conservation areas, 163 listed building entries and 3 Article 4 directions, and 17 per cent of its area is covered by green-belt polygons. Houses account for 61.5 per cent of households, so gardens are larger than in the inner boroughs.

Domestic gardens cover 30.9 per cent of the borough's land in the national land-use database. More garden means more scope for a lightwell or a cinema room, but also more trees, and tree roots are part of the ground and drainage assessment.

How the council treats householder schemes

The council decided 1,100 planning applications in its latest published year. It granted 83 per cent of householder applications but only 64.9 per cent of minor ones. Timing is the other number to watch: 92.5 per cent of householder cases and 80.1 per cent of minor ones were decided in time.

A basement application is judged with any extension above it. We prepare the full planning drawings in Kingston upon Thames so that the basement, the extension and the elevations tell one story.

Party wall and drainage rules for a Kingston upon Thames dig

Notice under the Party Wall etc. Act 1996 is needed for excavation within 3 metres of an adjoining building that goes deeper than its foundations, and within 6 metres on the diagonal test. Serve it at least 1 month before work. Our party wall notices service prepares the plans.

Building Regulations then address the floor. Where the water table can rise to within 0.25 metres of the lowest floor, it needs drainage or protection.

Cost and next step

There is no list price because ground, depth and tree cover change the scope. After the free constraints check we send a fixed quote and a note of what the council will expect.

The council can ask for more than the minimum list if the desk study raises a concern, so we allow for a modest second round of questions in our programme. Tell us early about any trees, any neighbour already worried about the dig and any plans for an extension above, because each of those changes what the investigation needs to cover.

We also send a short next-steps note with the quote. It lists who will do what, the order of the work and the points in the process where your decision is needed, so there are no surprises once the boreholes are drilled.