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 Weymouth?
In Weymouth, a single-storey extension typically costs £2,000–£2,950 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £40,000–£59,000. Prices in the South West sit near the national average for this kind of work, and the range for Weymouth reflects that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £28,000–£41,500 |
| Typical project (20 m²) | £40,000–£59,000 |
| Larger project (28 m²) | £56,000–£82,500 |
| Rate per m² | £2,000–£2,950 |
The main things that change the cost:
- Ground conditions and foundation depth
- How much of the existing house is opened up
- Kitchen, flooring and finishes, which we can include or leave to you
- Glazing: sliding and bifold doors cost more than French doors
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 Weymouth?
Whether you need planning permission depends on your house and its location 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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
On a typical single-storey extension we handle:
- Cavity walls, insulation and roof to current building regulations
- Foundations, drainage and any build-over agreement
- Structural calculations for steels and lintels
- Knock-through to the existing house with steel beams
- Building control inspections and completion certificate
- 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 Weymouth
The South West mixes stone and render cottages with post-war and newer estates, and local materials matter more here when matching an extension.
Projects in Weymouth (DT3 and DT4) are surveyed in person before we quote, so the price reflects your actual property.
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
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about single-storey extensions in Weymouth
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.
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 Weymouth?
In Weymouth, a single-storey extension typically costs £2,000–£2,950 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £40,000–£59,000. 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 Weymouth?
Yes. We build single-storey extensions across Weymouth, including postcodes DT3 and DT4. Every project starts with a free home visit.