Underpinning, basements and structural alterations in London

Underpinning deepens or replaces existing foundations, normally in engineered bays of mass concrete poured in a set sequence. A house needs it when the ground under the current foundation can no longer support it, usually shrinkable clay affected by a nearby tree, a leaking drain washing out fines, or an adjacent excavation. It is a last resort after monitoring, drain repair and tree management have been considered.

It is priced per bay rather than per house, so the number depends on how much of the perimeter is affected, how deep the bays go, access for spoil removal and whether temporary support is needed inside. Where subsidence is the cause, the buildings insurer often carries the cost after an engineer confirms it. We price from the engineer's design, and a firm figure follows a site visit and trial holes.

Yes, for any work that changes how load travels through the building. Building control will ask for calculations, and no competent contractor should cut a loadbearing wall without them. Our engineer produces the calculations, the beam sizing and the temporary works design as part of the contract, so you are not appointing separately and coordinating between two parties yourself.

Not for an internal wall in an unlisted house outside a conservation area, but Building Regulations always apply. Planning does come into it for a listed building, where internal alteration needs listed building consent, and where the work changes the external appearance. Removing a wall in a flat is usually a lease matter as well, requiring the freeholder's written consent.

Converting an existing cellar into habitable space: lowering the floor if head height demands it, forming a retaining structure, waterproofing to a defined grade, then drainage, escape provision, ventilation and light. It is different from excavating a new basement under a house, which is a larger job with its own planning position. Both need building control, and both usually trigger the Party Wall Act.

We lodge the building control application and book the inspections at each structural stage. On party wall matters we prepare and serve the notices at design stage and provide the drawings and calculations a surveyor asks for. The surveyor is appointed by you and, where a neighbour dissents, by them as well; those fees sit outside our contract because they are the neighbours' choice.

On site, two to four weeks for a single loadbearing opening with one steel, and four to eight for multiple openings or a full-width removal. Underpinning and basement work are quoted per project, because bay count, depth and spoil removal drive them. In every case, the party wall notice period in front of the work is often longer than the work itself.

Direction and thickness are indicators, not proof. A wall running at right angles to the floor joists, a wall that continues on the floor above, or a wall thicker than a stud partition should all be treated as structural until an engineer says otherwise. In many London terraces the chimney breast and the spine wall carry more than the front and rear walls do. We open a small area to check rather than guessing.

It is common and it is fixable. A structural engineer inspects what is there, and where the existing arrangement is adequate a regularisation application can be made to building control, which inspects and issues a certificate. Where it is not adequate, the remedy is usually a correctly sized beam and proper bearings. Either way it is better resolved before a sale than during one.