Two-storey extensions for semi-detached houses in County Durham

County Durham at a glance

Nation: England
Price region: North East England
Postcode areas: DH, DL, SR, TS
Towns covered: 19 listed below, plus surrounding villages
Approval route: Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission.
Site visits: Free, no obligation

What a two-storey extension for a semi-detached house involves

This service suits you if you own a semi-detached house and want to add bedrooms and living space without moving. On a semi, the main questions are which side to build on and how to treat the attached neighbour. You get a survey, design options, the approvals your nation needs and the build, carried out by vetted teams working under S&K.

County Durham towns we list: Darlington (DL1), Hartlepool (TS24), Stockton-on-Tees (TS18), Durham (DH1), Chester-le-Street (DH2) and Billingham (TS20). Every other address in County Durham is covered as well.

Guide price in North East England

In North East England, which includes County Durham, we'd expect a two-storey extension for a semi-detached house to cost around £50,500–£68,000 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), or £1,800–£2,430 per m² including VAT. Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	Typical project
Essential	£1,660–£2,240 per m²	£46,500–£62,500
Standard	£1,800–£2,430 per m²	£50,500–£68,000
Premium	£2,160–£2,920 per m²	£60,500–£81,500

Rules in England

In England, a two-storey rear extension on a semi can be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary, with matching materials and roof pitch. A two-storey side or wraparound extension always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026). Protected areas such as conservation areas exclude two-storey rear permitted development.

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

Rear, side or both

On a semi, a rear extension sits against the attached neighbour, while a side extension faces the detached neighbour and the street. We compare the space, cost and approval route for each, and for a wraparound, before you commit to one design.

Keeping the pair balanced

Semis are designed as matching pairs, and a side extension changes that balance. Setting the side extension back from the front wall and keeping its ridge lower helps the pair still read as a pair, which councils' design guides commonly ask for.

How we work in County Durham

Start at your house
We come to your home in County Durham, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering County Durham.
Structure and building control
A structural engineer sizes the foundations and steels, and we get building regulations approval before work starts.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Towns we cover in County Durham

Two-storey extensions for semi-detached houses in County Durham: questions

How much does a two-storey extension for a semi-detached house cost in County Durham?

In North East England our guide is £1,800–£2,430 per m² including VAT, so about £50,500–£68,000 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.

Should I extend my semi to the side or the rear?

It depends on your plot and what you need. A rear extension keeps the side drive and can sometimes be permitted development, but it affects the attached neighbour. A side extension keeps the rear garden but always needs planning permission in England. We compare both at the free site visit.

Will a side extension make my semi look like a terrace?

It can if it fills the whole gap to the boundary at first floor and the neighbour does the same. Many councils ask for a first-floor gap to the side boundary or a set-back for this reason. We design the extension to keep the semi reading as one of a pair.

Does a two-storey extension add value to a semi-detached house?

It usually adds value, but the gain is never certain. Nationwide's 2025 research found that 10% more floor area was linked to about 5% higher value, and that adding a double bedroom and bathroom to a three-bed, one-bathroom house could add up to 24%. Every street has a ceiling price, so check local sales first.

Will I need planning permission in County Durham?

County Durham is in England. Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission.

Neighbouring areas

All extension services in County Durham · About two-storey extensions for semi-detached houses