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 Caernarfon?
In Caernarfon, a single-storey extension typically costs £1,800–£2,650 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £36,000–£53,000. Prices across Wales are typically 8% below the UK average for this kind of work, which is reflected in the range for Caernarfon. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £25,000–£37,000 |
| Typical project (20 m²) | £36,000–£53,000 |
| Larger project (28 m²) | £50,500–£74,000 |
| Rate per m² | £1,800–£2,650 |
The biggest cost drivers are:
- Kitchen, flooring and finishes, which we can include or leave to you
- Ground conditions and foundation depth
- Roof type and the size of any lantern or roof windows
- How much of the existing house is opened up
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a single-storey extension in Caernarfon?
Whether you need planning permission depends on your house and its location in Wales. In Wales a single-storey rear extension is often permitted development: up to 4 metres beyond the rear wall and up to 4 metres high, with eaves no higher than 3 metres within 2 metres of a boundary and no more than half the land around the original house covered. Wales has no larger home extension prior approval route, so deeper extensions need a planning application, as do extensions to flats, listed buildings and houses whose rights have been removed.
The Party Wall etc. Act 1996 applies in Wales, so notices must be served before work on a shared wall, on the boundary, or excavation close to a neighbour’s foundations.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
The work we manage on a single-storey extension:
- Cavity walls, insulation and roof to current building regulations
- First and second fix electrics, heating and plastering
- Doors, windows and roof glazing installed
- Foundations, drainage and any build-over agreement
- Building control inspections and completion certificate
- Measured survey and design drawings
How long does it take?
Build time is typically 10 to 14 weeks on site for a typical rear extension, after approvals. Design and approvals come first and typically take 6 to 12 weeks, depending on the approval route.
Building in Caernarfon
Terraced houses in Welsh towns often have narrow plots, which suits rear and side return extensions and rear dormers.
Projects in Caernarfon (LL55) are surveyed in person before we quote, so the price reflects your actual property.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about single-storey extensions in Caernarfon
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.
Who approves a single-storey extension in Caernarfon?
Planning matters in Caernarfon go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
Can I stay in the house during the build?
Usually yes. We build the shell before opening up the back wall, so the house stays weathertight for most of the job. There will be a few weeks when the kitchen or back room is out of use.
Do I need planning permission for a single-storey extension in Caernarfon?
In Wales a single-storey rear extension is often permitted development: up to 4 metres beyond the rear wall and up to 4 metres high, with eaves no higher than 3 metres within 2 metres of a boundary and no more than half the land around the original house covered. Wales has no larger home extension prior approval route, so deeper extensions need a planning application, as do extensions to flats, listed buildings and houses whose rights have been removed.
How much does a single-storey extension cost in Caernarfon?
In Caernarfon, a single-storey extension typically costs £1,800–£2,650 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £36,000–£53,000. Your fixed price depends on the survey and drawings.
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.