Design and build two-storey extensions in Wiltshire

Wiltshire at a glance

Nation: England
Price region: South West England
Postcode areas: BA, SN, SP
Towns covered: 14 listed below, plus surrounding villages
Site visits: Free, no obligation

What a design and build project involves

A design and build project for a two-storey extension involves one team taking responsibility for the whole job: the survey, design, planning or permitted development, structural engineering, building regulations, party wall matters where they apply and the construction itself. You deal with one point of contact instead of coordinating an architect, engineer and builder separately. The design stage is priced first, then the build at a fixed price.

Across Wiltshire we cover Swindon (SN1), Salisbury (SP1), Trowbridge (BA14), Chippenham (SN15), Melksham (SN12) and Warminster (BA12), plus the smaller places around them.

Fees

The design stage is priced in writing before it starts, and the build is a fixed price in writing once the design is agreed.

Rules in England

In England, design and build covers the permitted development check or planning application (£548 (or £575 for applications made from 8 December 2026)), building regulations approval from council building control or a registered approver, Party Wall Act notices where needed, and the Building Safety Act dutyholder roles. We programme them so they overlap where possible.

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

Responsibility for the rules

In England, where more than one contractor is involved, a principal designer and principal contractor must be appointed. On design and build projects we take on these duties, so you are not left holding responsibilities you may not know you had.

Cost checking as you design

Because the people drawing the extension also build it, each design option comes with a guide cost. That avoids the common problem of an approved design that turns out to be too expensive once builders price it.

How we work in Wiltshire

Free site visit
We visit your home in Wiltshire, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
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 Wiltshire

Design and build two-storey extensions in Wiltshire: questions

Who builds my extension?

Your extension is built by vetted teams working under S&K, with the project managed by us from design to completion. You have one point of contact throughout, and the same team that prepared the design is responsible for the build.

What is the difference between design and build and using an architect?

With an architect, you appoint them for the design and approvals, then find and manage a builder separately. With design and build, one team does both, so cost, buildability and approvals are considered together and there is one point of contact. Some people still prefer to hire an architect separately.

Do I have to use you for the build if I pay for the design stage?

No. The design stage is priced separately, so you can take the approved drawings to other builders if you choose. Most people who use design and build carry on to the build, because the design has been costed as it developed.

Neighbouring areas

All extension services in Wiltshire · About design and build two-storey extensions