Building regulations for 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 building regulations application involves

This service suits every two-storey extension, because each one needs building regulations approval wherever you live in the UK. You get technical drawings and a specification coordinated with the structural engineer, a full plans application, site inspections arranged at each stage, and the completion certificate you will need when you sell. We manage the process, and the work is carried out by vetted teams working under S&K.

The main places we list in Wiltshire are Swindon (SN1), Salisbury (SP1), Trowbridge (BA14), Chippenham (SN15), Melksham (SN12) and Warminster (BA12). We cover the villages in between too.

Fees

Technical drawings and specification are a guide of £1,500–£4,000. The council's building control fee depends on the value of the work; we confirm every fee in writing before the design stage starts.

Rules in England

In England, building regulations approval comes from council building control or a registered building control approver, using the Approved Documents. Full plans are recommended for two-storey work. New editions of Approved Documents L and F take effect generally from 24 March 2027 and are not yet in force, so current projects follow the 2021 standards.

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

Insulation and U-values

In England, Part L sets limiting U-values for extensions: 0.18 W/m²K for walls, 0.15 for roofs, 0.18 for floors and 1.4 for windows. Glazing is normally limited to 25% of the new floor area plus windows removed, unless SAP or compensating calculations are used.

Fire escape from the first floor

In England, first-floor habitable rooms need an escape window, with a clear opening of at least 0.33 m², at least 450 mm wide and high and its bottom no more than 1,100 mm above the floor, or a protected stair. Adding a storey above 4.5 m means a protected stairway or an alternative.

How we work in Wiltshire

Look at the house
We start in Wiltshire with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Get it approved
Once you're happy with the design we submit it to the council for Wiltshire and deal with any questions from the planning officer.
Fixed price in writing
With approved drawings and calculations, we give you a fixed build price and a programme you can plan around.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

Towns we cover in Wiltshire

Building regulations for two-storey extensions in Wiltshire: questions

What is a build-over agreement?

A build-over agreement is permission from your water company to build over or near a public sewer. Many rear extensions sit near shared drains, and the water company will want access protected and the pipe checked. We check sewer records early so the agreement does not delay the start.

Do I need building regulations if I have planning permission?

Yes. Planning permission and building regulations are separate. Planning covers what the extension looks like and how it affects neighbours; building regulations cover how it is built and whether it is safe, warm and healthy. A two-storey extension needs both, unless permitted development replaces the planning part.

Are the new 2027 building regulations going to affect my extension?

New editions of Approved Documents L and F take effect generally from 24 March 2027 in England, and are not in force yet. Projects approved under the current rules follow the 2021 standards. If your build will start after that date, we check whether transitional arrangements apply.

Neighbouring areas

All extension services in Wiltshire · About building regulations for two-storey extensions