Seaham, County Durham
Semi-detached rear extension in Seaham
Single or two-storey extensions for semi-detached houses, with side access and one party wall. If you live in Seaham and want to know what a semi-detached rear extension would cost and whether it needs planning, start with the online guide price or a free site visit.
Seaham and its postcode districts SR7 are part of our County Durham coverage. Where a Seaham semi already has a small lean-to at the back, we usually replace it rather than extend it.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a semi-detached rear extension cost in Seaham?
For Seaham we work from the North East England rate: £1,710–£2,790 per square metre of new floor, including VAT, standard specification. North East prices are among the lowest in our range; former mining ground is the main foundation variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £20,500–£33,500 |
| 4 m wide × 5 m deep (20 m²) | £34,000–£56,000 |
| 4 m wide × 6 m deep (24 m²) | £41,000–£67,000 |
We put a fixed price in writing once the design is agreed, and explain any provisional sums such as foundations.
Do you need planning permission for a semi-detached rear extension in Seaham?
Here is how the rules in England apply to a semi-detached rear extension in Seaham.
Under England's householder permitted development rules you can usually add 3 metres at the back of an attached house, or 4 metres on a detached house, without a planning application, as long as the extension stays under 4 metres high and its eaves stay under 3 metres where it is within 2 metres of a boundary.
A two-storey rear extension can be permitted development in England only if it projects no more than 3 metres, stays at least 7 metres from the rear boundary, matches the existing roof pitch and has obscure-glazed upper side windows. In practice most double-storey rear extensions go through a householder planning application.
If 3 or 4 metres is not enough, England's prior approval route allows 6 metres on a terraced or semi-detached house and 8 metres on a detached house for a single-storey rear extension. Neighbours are consulted, the council decides within 42 days, and the fee is £249, rising to £310 from 8 December 2026.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent. At the first visit we measure what is there now and tell you which route fits: permitted development, prior approval or a planning application.
What are homes in Seaham like to extend?
Brick terraces, colliery houses and post-war semis make up much of Seaham. Former mining areas often need a coal mining risk check before foundations are designed.
How a semi-detached rear extension in Seaham comes together
Look round and measure
A free visit to see the back of the house, measure it, check the drains and boundaries and hear what you need.
Options and costs
We draw layout options and price each one, so the budget shapes the design rather than surprising you later.
Planning and regulations
We take the design through the right planning route, then produce the construction drawings and engineer's calculations for building control.
Written price, then build
Once the design and approvals are in place, you get a fixed written price and programme, and we build through to sign-off.
Semi-detached rear extensions near Seaham
We also build rear extensions for semi-detached houses in nearby Ryhope (2.4 miles) and Hetton-le-Hole (4.4 miles).
- Semi-detached rear extension in Ryhope
- Semi-detached rear extension in Hetton-le-Hole
- Semi-detached rear extension in Houghton-le-Spring
- Semi-detached rear extension in Sunderland
- Semi-detached rear extension in Peterlee
Other work in Seaham:
FAQ
Semi-detached rear extension questions in Seaham
Will I need a structural engineer?
Yes for the beam over the new opening and usually the foundations; we arrange them and their calculations go to building control.
Do I need planning permission for a rear extension in Seaham?
Often not for a single-storey rear extension of up to 3 metres (4 metres on a detached house) under permitted development, or up to 6 or 8 metres with prior approval, unless the house is in a conservation area or its rights have been removed.
How long does a semi extension take?
10 to 16 weeks on site for a single-storey extension.
Can you match the brick or stone on my Seaham house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.
Do I need a party wall agreement?
In England, usually yes if the extension is on or near a shared boundary or the foundations are close to a neighbour's building. We serve the notices.
How much does a semi-detached rear extension cost in Seaham?
As a guide, £1,710–£2,790 per square metre including VAT for a standard specification. For example, 3 m wide × 4 m deep (12 m²): about £20,500–£33,500 at that rate. Your written price follows the survey.