Structural engineering for two-storey extensions in Gwynedd and Anglesey

Gwynedd and Anglesey at a glance

Nation: Wales
Price region: Wales
Postcode areas: LL
Towns covered: 10 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.

Gwynedd and Anglesey towns we list: Bangor (Gwynedd and Anglesey) (LL57), Holyhead (LL64), Caernarfon (LL54), Llangefni (LL60), Bethesda (LL57) and Pwllheli (LL51). Every other address in Gwynedd and Anglesey 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 Wales

In Wales, structural design is checked under the Welsh building regulations, Part A, as part of a full plans application to building control. The engineer's calculations and drawings are submitted with the architectural drawings, and the building control surveyor inspects foundations and key structural stages on site.

Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.

Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).

The Party Wall etc. Act 1996 applies in Wales, 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.

Building on existing structure

When building over a garage or a single-storey extension, the engineer checks the existing footings, walls and lintels. Many were sized for one storey only and need underpinning, strengthening or replacement to carry the new floor.

How we work in Gwynedd and Anglesey

Start at your house
We come to your home in Gwynedd and Anglesey, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Get it approved
Once you're happy with the design we submit it to the council for Gwynedd and Anglesey and deal with any questions from the planning officer.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.

Towns we cover in Gwynedd and Anglesey

Structural engineering for two-storey extensions in Gwynedd and Anglesey: questions

Can a steel beam be hidden in the ceiling?

Often, yes. A beam can sit within the floor depth so the ceiling is flat, but that may mean a deeper steel section or a different floor structure. Otherwise it shows as a downstand below the ceiling. We discuss the options with you and the engineer before the design is fixed.

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.

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.

Neighbouring areas

All extension services in Gwynedd and Anglesey · About structural engineering for two-storey extensions