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 Monmouth?
In Monmouth, 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. The guide for Monmouth reflects typical costs in Wales, roughly 8% below the UK-wide figure. 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 |
What moves the price most:
- Ground conditions and foundation depth
- Glazing: sliding and bifold doors cost more than French doors
- Floor area and the length of new wall
- Kitchen, flooring and finishes, which we can include or leave to you
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a single-storey extension in Monmouth?
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.
Building regulations in Wales are set by the Welsh Government. Approval comes from the council’s building control service or a registered building control approver, with inspections during the work and a completion certificate at the end.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
What we take care of:
- Cavity walls, insulation and roof to current building regulations
- Building control inspections and completion certificate
- Structural calculations for steels and lintels
- First and second fix electrics, heating and plastering
- Foundations, drainage and any build-over agreement
- Measured survey and design drawings
How long does it take?
Allow 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 Monmouth
Terraced houses in Welsh towns often have narrow plots, which suits rear and side return extensions and rear dormers.
Monmouth sits in Gwent, about 20 miles north-east of Newport. We cover the whole of Monmouth, including postcodes NP25.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about single-storey extensions in Monmouth
Who approves a single-storey extension in Monmouth?
Planning matters in Monmouth go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
Do I need planning permission for a single-storey extension in Monmouth?
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.
What is a build-over agreement?
If a public sewer runs within 3 metres of the extension, the water company normally has to agree to the work before it starts. We check sewer records during design and apply where needed.
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.
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.
How much does a single-storey extension cost in Monmouth?
In Monmouth, 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.