Structural calculations in Westminster

Basement limits written into the City Plan

If a basement is on the table, Westminster has numbers to design around. The basement policy sets out 50% garden; 1 storey; 1 m soil + 200 mm drainage; 1.8 m / 900 mm highway, and the supporting text describes the most appropriate basement as no more than about 2.7 m storey below the lowest original floor.

The council also wants evidence of how construction will be handled: Signed CoCP Appendix A; neighbour engagement evidence may be requested. A signed pro forma is easy to forget and slow to obtain late in the process.

In the higher flood zones a flood risk assessment accompanies the structural statement. For small extensions the council accepts a simple version, which keeps the paperwork in proportion to the project.

Fees and the building control route

The council's schedule of charges, effective from April, sets the charge for opening a load-bearing wall. For a through-lounge in a structural wall it lists GBP 900.00 inc VAT (full plans or building notice); effective 1 April 2026. Work started without approval is charged as regularisation, which the schedule sets at Regularisation 150% of fee.

Those are council charges, paid to Westminster and separate from our fee.

Mews houses, roofs and listed buildings

Only 10.2 per cent of Westminster's households live in a house or bungalow, so many structural jobs are in flats, mews houses and upper floors of large terraces. The council publishes Mews: a guide to alterations SPG and Roofs: a guide to alterations and extensions on domestic buildings SPG, which govern what can be done to a roof or a mews elevation, and those drawings must agree with the structure underneath.

Westminster has 56 conservation areas, 10 Article 4 directions and 4,015 listed entries. For a listed building, the City Plan notes: Listed buildings: excavation damage and hierarchy of spaces. So excavation and the loss of an original layout are treated as heritage harm, not only as engineering risk.

Where demolition is part of the scheme, the council expects the applicant to show why retention is not possible. A calculation that proves an existing wall or floor can carry the new load is the best evidence for retention.

Fee, deliverables and access

Our fee for the calculations is £295 or more, VAT included and fixed once the constraints check is done. You receive the calculations, a beam and padstone schedule and a layout drawing, normally about a week after the survey. A second technologist checks everything, and we revise at no charge if the examiner asks for changes.

Where a job involves a freeholder, a managing agent and neighbours above or below, we write the calculation so that each of them can see the load path and the assumptions made about the floors around the opening. It also helps the builder, who receives a schedule that says which beam goes where and what bears it.

Access can be as much of a constraint as structure in central streets, with parking suspensions, restricted hours and narrow stairs. Tell us early how steel will reach the flat, because the length of each piece may decide how a long beam is split into sections.

A basement is quoted separately, because it needs specialist surveys that the calculation alone does not cover.

Further reading

The service is described on our structural calculations page. For Westminster as a whole, see architectural drawings in Westminster, and for how the figures reach the construction set, building regulations drawings in Westminster. Across the boundary, Camden asks for a different set of reports.