Structural engineering in London

What the structural design includes

A typical package has four parts. Calculations prove that each beam, lintel and foundation is strong enough. Drawings show them: beam positions, sizes, bearing details, padstones and temporary works notes. A specification names the steel grade and concrete mix. And a coordination check confirms that the structure fits in the ceiling depths, wall thicknesses and floor build-ups the architectural set shows.

That last step is where separate firms can trip. A beam that works on paper but is deeper than the ceiling void has to be redesigned, often once a builder is standing under it. We model structure and architecture together, so the clash shows up on screen, not on site.

Our structural calculations service covers the calculation package on its own, for cases where the drawings are already settled. The engineering page you are reading covers the wider design, including foundations, underpinning and larger alterations.

The regulations behind it, in plain English

Part A of Schedule 1 to the Building Regulations has three requirements. The first deals with loading: A1(1): the building shall be constructed so that the combined dead, imposed and wind loads are sustained and transmitted by it to the ground (a) safely; and (b) without causing such deflection or deformation of any part of the building, or such movement of the ground, as will impair the stability of any part of another building. A1(2): regard shall be had to the imposed and wind loads to which it is likely to be subjected in the ordinary course of its use for the purpose for which it is intended.. The second deals with ground movement and the third with disproportionate collapse, so they are summarised in the guidance as A1 loading; A2 ground movement; A3 disproportionate collapse.

The adopted guidance dates from the 2004 edition incorporating 2004, 2010 and 2013 amendments, and it points designers to the Eurocodes: AD A names BS EN 1990 to BS EN 1999 (Eurocodes 0 to 9, including EN 1991-1-7 on accidental actions) with their UK National Annexes, and PD 6688-1-7, PD 6687-1, PD 6693-1 and PD 6697, as the structural design standards; BS 8103-1, -2 and -3 cover low-rise housing foundations, masonry and timber floors and roofs. Calculations are done to those standards, which is why they cannot be copied from a neighbour's job.

Roof work has a trigger of its own. The guidance sets a threshold of 15 per cent for an increase in roof load before the supporting structure must be checked. The simplified rules also cap the load on a wall at 70 kN/m, and a floor may span no more than 6 metres onto it.

Lofts, extensions and basements: different structural problems

A loft conversion usually means new steel across the house, with the floor joists strengthened and the roof structure altered. Permitted development limits the added volume: Class B loft enlargement: resulting roof space must not exceed the original by more than 40 m3 (terrace house) or 50 m3 (any other case); no part may exceed the height of the highest part of the existing roof or extend beyond the principal roof plane fronting a highway; original eaves maintained or reinstated and the enlargement, so far as practicable, at least 0.2 m from the eaves along the slope; no part beyond the outside face of any external wall of the original dwellinghouse (except hip-to-gable or joining to a rear or side extension). Our loft conversion drawings service pairs the design with the planning route.

A rear or side extension is mainly about the opening in the old wall, the new foundation and where the roof loads end up. Soil, nearby trees and drains decide how deep the foundation goes, so the survey and trial pits come before the final design.

A basement is the most demanding job. It involves underpinning or a new retained box, groundwater, temporary propping and neighbours. Check our basement impact assessment page, as some councils ask for one before they decide.

Neighbours, party walls and building control

Structural work often touches a shared wall, and that triggers the Party Wall etc. Act 1996. A party structure notice must be served at least 2 months ahead, and an excavation near a neighbour's foundations needs 1 month's notice. Our party wall notices service handles the paperwork, using the structural drawings as the attachment.

Building control then checks the design. Full plans applications are decided within 5 weeks under the current regulations, and the regulations require notice 2 days before starting on site. A building notice route lapses after 3 years if not progressed. Structural drawings are the usual first thing an inspector asks to see.

Designers also have personal duties: Reg 11F: any person carrying out design work must have the skills, knowledge, experience and behaviours (or organisational capability) to carry out the design work so that the building work, if built, would accord with all relevant requirements. Reg 11K(2): a designer must take all reasonable steps to ensure the design, if built, would comply with all relevant requirements.. That is a further reason to use a competent firm for structural design and not a builder's guess.

How the quote works

We do not publish a starting price for structural engineering, because a single steel beam and a basement are not the same job. We run a free constraints check first, ask for photographs and any existing drawings, and then give a fixed quote.

TODO (owner): confirm the engineer's credentials (for example CEng, MIStructE) and whether structural design is delivered in-house or through a partner

The words structural engineer are not a legally protected title, according to the Engineering Council, so it is reasonable to ask anyone you instruct what qualification they hold.

Structural engineering by borough

Ground, housing stock and conservation rules vary a great deal across London. London clay under a terrace in one borough is a different problem from a sloping site in another. Our council pages set out the local designations that decide how structural work can be seen from the street. Start with Camden's planning facts, or browse architectural drawings by area.