Structural calculations in London

The rules behind the numbers

The relevant guidance is Approved Document A, which covers structure. It gives simple rules for common cases. For masonry walls in residential buildings of not more than three storeys, its wall-thickness rules apply. For floors supported by a wall, the simple rules cover a span of up to 6 metres between bearing centres.

Beyond the simple rules, calculation is the route. That means checking each member for bending, shear and deflection, and the bearing it sits on. The figures in the table show the scope and the limits we work to.

The design also has to resist disproportionate collapse, which sets how much robustness is needed.

The calculation also records the loads assumed for floors, roof and finishes, so a later change of roof covering can be tested against the original design.

Where a calculation is most often needed

Three jobs come up again and again: removing a chimney breast or a wall between rooms, forming a wide opening in a rear extension, and converting a loft. Each needs a beam or a new floor structure, and each needs the existing walls checked for the extra load.

In a loft the floor joists are rarely big enough for habitable use, so new joists or steel are designed. In a rear extension the large glazed opening is carried by a beam, and its end bearings carry point loads down to the foundation.

We pick these up in the survey, noting wall thicknesses and what is above and below each opening, so the calculation starts from facts instead of assumptions.

Existing walls matter as much as the new beam. We record whether a wall is solid brick or cavity, its thickness and any chimney stack above, because those details decide the loads that reach each bearing.

How our structural service works

We prepare the architectural drawings, set out the structural intent and coordinate the calculations with a structural engineer, so the structure is designed alongside the building rather than added after. The beams on our sheets are the beams in the calculation.

A change to an opening is made once in the Revit model and flows to every sheet. A technologist who did not draft it checks the set before it goes to building control, and the engineer's output is checked against it.

Our building regulations drawings use the calculations directly, and the complete package covers planning, building regulations and structural together.

Party walls and excavation near neighbours

Structural work often touches the boundary. Under the Party Wall etc. Act 1996 you must serve an adjacent excavation notice at least one month before work if you dig within a set distance of a neighbour's building and deeper than their foundations. The exact tests are in the table.

Our party wall notices service prepares the notices and the drawings that go with them. Serving them early avoids a dispute that stops the build.

If your project needs more than calculations, such as engineered design for a basement or a complex frame, our structural engineering page describes that wider service.

Price and what you receive

Structural calculations start at £295 including VAT, as a fixed fee confirmed after the constraints check. Larger or more complex structures are quoted from the same price list.

You receive the calculations, the beam and padstone schedule and a layout drawing. Expect the package roughly a week after the survey; if building control wants changes, we revise at no extra charge.