Structural engineering for two-storey extensions in Buckinghamshire

Buckinghamshire at a glance

Nation: England
Price region: South East England
Postcode areas: HP, MK, SL
Towns covered: 13 listed below, plus surrounding villages
Site visits: Free, no obligation

What a structural design involves

Structural engineering for a two-storey extension involves calculating how the new floors, walls and roof carry their loads down to the ground, and designing the beams, lintels, foundations and ties into the existing house to suit. The engineer's calculations and drawings form part of the building regulations approval. They also tell the build team exactly what steel and foundations to install.

Buckinghamshire towns we list: Milton Keynes (MK5), High Wycombe (HP11), Aylesbury (HP17), Bletchley (MK1), Amersham (HP7) and Chesham (HP5). Every other address in Buckinghamshire is covered as well.

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

Beams and padstones

Steel beams carry the first floor and roof over openings, and they sit on padstones that spread the load into the walls. The engineer sizes each beam and checks the walls can take the point loads, which affects ceiling heights and where posts can go.

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 Buckinghamshire

Start at your house
We come to your home in Buckinghamshire, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Towns we cover in Buckinghamshire

Structural engineering for two-storey extensions in Buckinghamshire: 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 Buckinghamshire · About structural engineering for two-storey extensions