Building regulations for two-storey extensions in Dorset

Dorset at a glance

Nation: England
Price region: South West England
Postcode areas: BH, DT, SP
Towns covered: 16 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.

Across Dorset we cover Bournemouth (BH1), Poole (BH15), Weymouth (DT3), Christchurch (BH6), Ferndown (BH22) and Dorchester (DT1), plus the smaller places around them.

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

Full plans and inspections

Full plans approval checks the design before work starts, which we recommend for two-storey extensions. Building control then inspects key stages, such as foundations, damp-proofing, drainage and insulation, before issuing the completion certificate.

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 Dorset

Free site visit
We visit your home in Dorset, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Drawings, then consent
We draw the scheme, check it against the rules in England, and take it through the right consent with the council.
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 Dorset

Building regulations for two-storey extensions in Dorset: questions

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.

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.

Neighbouring areas

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