Structural engineering for two-storey extensions in Surrey

Surrey at a glance

Nation: England
Price region: South East England
Postcode areas: CR, GU, KT, RH, SM, TW
Towns covered: 35 listed below, plus surrounding villages
Site visits: Free, no obligation

What a structural design involves

This service suits every two-storey extension, because each one needs foundations sized for two storeys and usually steel beams where walls are removed. You get a structural engineer's calculations and drawings for beams, padstones, lintels, foundations and connections, coordinated with the architectural drawings, submitted for building control and followed through on site by our build teams.

The main places we list in Surrey are Woking (GU21), Guildford (GU1), Esher (KT10), Redhill (RH1), Staines (TW18) and Banstead (KT20). We cover the villages in between too.

Fees

A structural engineer (calculations and beam design) is a guide of £750–£2,200, priced in writing once the design is known.

Rules in England

In England, structural engineering is part of building regulations approval under Part A rather than planning. The engineer's calculations go to council building control or a registered building control approver with the full plans application. Where more than one contractor is involved, the Building Safety Act dutyholder rules also apply.

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.

Getting the design right

Foundations for two storeys

Two storeys put more load on the ground than one, so foundations are usually deeper or wider. Clay soil, nearby trees, drains and made-up ground can all mean deeper trench fill or piles, which is why we dig trial holes before fixing the design.

Tying into the house

The new walls and floors are tied into the existing house with wall ties, restraint straps and joist hangers. The engineer also considers movement between the old and new foundations and where a movement joint may be needed.

How we work in Surrey

Measure and listen
A visit to Surrey to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Design and approvals
We draw the extension and check it against the rules for England, then apply for planning permission or a certificate of lawfulness, whichever fits.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Towns we cover in Surrey

Structural engineering for two-storey extensions in Surrey: questions

Will the engineer visit the site during the build?

Not usually at every stage. Building control inspects the foundations, steelwork and other key stages against the approved calculations. The engineer is called back if site conditions differ from the design, such as unexpected ground, hidden beams or weak existing walls, and issues revised details before that part of the work continues.

Do I need a structural engineer for a two-storey extension?

Almost always. Building control needs calculations showing that the foundations, beams and walls can carry the loads of two storeys and a roof. A two-storey extension usually involves removing part of an outside wall and new steel, which needs an engineer's design.

What are trial holes and why do I need them?

Trial holes are small excavations dug next to the house or garage to see the depth and condition of the existing foundations and the soil. They tell the engineer whether existing footings can be reused and how deep the new ones need to go, which avoids surprises during the build.

Neighbouring areas

All extension services in Surrey · About structural engineering for two-storey extensions