Two-storey rear extensions in Dorchester

What we'd confirm first for a project in Dorchester.

Postcode districts: DT1 and DT2
County / area: Dorset, England
Price region: South West England
Guide price: £57,500–£78,000 (£2,060–£2,780 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
Nearest towns: Weymouth (7.2 miles), Portland (10.3 miles), Bridport (14.3 miles)
Distance to Bournemouth: about 24.2 miles
First visit: Free, no obligation

About a two-storey rear extension

A two-storey rear extension is a new two-floor addition built onto the back of your house, usually giving a larger kitchen or living space on the ground floor and one or two bedrooms or a bathroom above. Because both floors share one set of foundations and one roof, it adds a lot of floor space for the garden it uses. In some cases it can be built under permitted development, depending on where you live.

Around Dorchester we also work in Weymouth, Portland and Bridport, and across the rest of Dorset. Postcode districts in and near Dorchester: DT1 and DT2.

What it costs in Dorchester

For budgeting in Dorchester, allow around £57,500–£78,000 for a two-storey rear extension with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). That's based on £2,060–£2,780 per m² including VAT for South West England. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

Spec	Per m²	A 4 m × 3.5 m footprint on two floors (28 m² of new floor space)
Essential	£1,900–£2,560 per m²	£53,000–£71,500
Standard	£2,060–£2,780 per m²	£57,500–£78,000
Premium	£2,470–£3,340 per m²	£69,000–£93,500

Planning and building regulations in Dorchester

In England, a two-storey rear extension can be permitted development if it goes no more than 3 m beyond the rear wall of the original house, stays at least 7 m from the rear boundary and matches the house's materials and roof pitch. It is not permitted development in conservation areas, National Landscapes, National Parks, World Heritage Sites or the Broads. Otherwise a householder application costs £548 (or £575 for applications made from 8 December 2026).

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.

Design points for Dorchester homes

Foundations and drains

Foundations for two storeys carry more load than a single storey and may need to go deeper near trees or on clay. Rear extensions often sit near drains, so we check sewer records early, as building over or near a public sewer may need the water company's agreement.

Roof form

A hipped or gabled roof that matches the pitch of the main house usually looks best, and matching the pitch is a permitted development condition in England. Keeping the ridge below the main ridge makes the extension read as secondary and avoids awkward junctions with existing gutters and windows.

How we'd run your project

Look at the house
We start in Dorchester 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 Dorchester and deal with any questions from the planning officer.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.

Questions about two-storey rear extensions in Dorchester

Which postcodes do you cover around Dorchester?

We cover Dorchester (DT1 and DT2) and nearby places including Weymouth, Portland and Bridport, plus the rest of Dorset. The first site visit is free.

How long does a two-storey rear extension take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils should decide householder applications within 8 weeks of validation), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.

Do I need planning permission for a two-storey rear extension in Dorchester?

Dorchester is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

Can I have a balcony on a two-storey rear extension?

In England, balconies, verandas and raised platforms are not permitted development, so a balcony on a two-storey rear extension needs planning permission. A Juliet balcony, a guard rail across full-height doors with no platform to stand on, is often a practical alternative, but it still needs checking against the rules and the council's approach to overlooking.

Will a two-storey rear extension block my neighbour's light?

It can if it is too deep or too close to the boundary, which is why councils look closely at its effect on neighbouring windows and gardens. We test the design against light and outlook early, keep the first floor shorter or set in where needed, and use a hipped roof to reduce bulk on the boundary side.

Nearby

Other towns near Dorchester:

Other extensions in Dorchester

All two-storey extension services in Dorchester · Two-storey rear extensions across Dorset

Tell us about your house in Dorchester and we'll call you back to arrange a free, no-obligation visit.