Building regulations for two-storey extensions in Somerset

Somerset at a glance

Nation: England
Price region: South West England
Postcode areas: BA, BS, TA
Towns covered: 18 listed below, plus surrounding villages
Site visits: Free, no obligation

What a building regulations application involves

Building regulations approval for a two-storey extension involves preparing technical drawings and a specification that show how the extension meets the rules on structure, fire safety, insulation, ventilation, electrics and drainage, getting them approved and having the work inspected. At the end you receive a completion certificate.

Somerset towns we list: Bath (BA1), Weston-super-Mare (BS22), Taunton (TA1), Yeovil (BA20), Bridgwater (TA5) and Portishead (BS20). Every other address in Somerset is covered as well.

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.

Dutyholders in England

Since October 2023, where more than one contractor is involved, a principal designer and principal contractor must be appointed. For domestic clients these duties normally pass to the contractor and designer, so on our projects we take them on.

How we work in Somerset

Understand the brief
At your home in Somerset we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Structure and building control
A structural engineer sizes the foundations and steels, and we get building regulations approval before work starts.
Build and sign-off
Vetted teams working under S&K build the extension, and we arrange the building control completion certificate at the end.

Towns we cover in Somerset

Building regulations for two-storey extensions in Somerset: 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.

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.

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.

Neighbouring areas

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