What is a single-storey extension?
A single-storey extension is a ground-floor addition, usually at the rear of a house, that enlarges a kitchen, living or dining space. Most are built with cavity walls on concrete foundations and finished with a flat roof and roof lantern or a pitched tiled roof.
How much does a single-storey extension cost in Seaham?
In Seaham, a single-storey extension typically costs £1,750–£2,600 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £35,000–£52,000. We start from a UK-wide guide and adjust it for the North East, where labour and materials are typically about 10% below average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £24,500–£36,500 |
| Typical project (20 m²) | £35,000–£52,000 |
| Larger project (28 m²) | £49,000–£73,000 |
| Rate per m² | £1,750–£2,600 |
Your quote will depend mainly on:
- Roof type and the size of any lantern or roof windows
- Ground conditions and foundation depth
- Kitchen, flooring and finishes, which we can include or leave to you
- How much of the existing house is opened up
Use the guide price tool to see how size and specification change the figure, then ask for a written, itemised quote.
Do you need planning permission for a single-storey extension in Seaham?
Before anything is built in Seaham, we confirm which approvals apply in England. In England a single-storey rear extension is often permitted development: broadly up to 3 metres deep on a semi-detached or terraced house and 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary, and covering no more than half the garden. The larger home extension scheme allows up to 6 or 8 metres if you notify the council first and neighbours have a chance to comment. In conservation areas, National Parks and National Landscapes the larger home extension route, side extensions and cladding are not permitted development. Flats and houses whose rights have been removed need a planning application, and listed buildings need listed building consent.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
What we take care of:
- Building control inspections and completion certificate
- Cavity walls, insulation and roof to current building regulations
- Measured survey and design drawings
- First and second fix electrics, heating and plastering
- Foundations, drainage and any build-over agreement
- Structural calculations for steels and lintels
How long does it take?
Build time is typically 10 to 14 weeks on site for a typical rear extension, after approvals. Allow time beforehand for drawings and approvals, usually 6 to 12 weeks.
Building in Seaham
The North East has many terraced streets and post-war semis, where rear extensions and loft conversions are popular ways to gain space.
Our Seaham coverage includes postcode districts SR7, and we also work in nearby places such as Houghton-Le-Spring, Sunderland and Peterlee.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about single-storey extensions in Seaham
How long does a single-storey extension take?
Once approvals are in place, a typical rear extension takes 10 to 14 weeks on site. Design and approvals usually take another 6 to 12 weeks beforehand, depending on whether a planning application is needed.
How much does a single-storey extension cost in Seaham?
In Seaham, a single-storey extension typically costs £1,750–£2,600 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £35,000–£52,000. Your fixed price depends on the survey and drawings.
Do I need planning permission for a single-storey extension?
Not always. Many small rear extensions are permitted development, within limits on depth, height and how much of the garden is covered. The limits depend on which nation you live in and on protected areas such as conservation areas, and flats or houses whose rights have been removed need an application. We check this at the survey and can apply to the council for formal confirmation.
Do you build single-storey extensions in Seaham?
Yes. We build single-storey extensions across Seaham, including postcodes SR7. Every project starts with a free home visit.
Is VAT charged on an extension?
Yes. Building work on an existing home is standard-rated, so VAT at 20% applies. Our guide prices include it.