A single-storey extension is a new ground-floor room built onto your house, usually at the rear or side, with its own foundations, walls and roof, creating a bigger kitchen, living space or bedroom without moving home.
South Glamorgan is part of our UK-wide coverage for a single-storey extension. Places we cover include Cardiff, Barry, Penarth and Llantwit Major, and we travel to smaller communities across the area as well. Since your property is in Wales, the relevant planning and building rules are the ones set there. In Wales, budget around £32,000–£69,000 with VAT; the figure is confirmed after a survey that costs you nothing.
- Guide price
- £32,000–£69,000 inc VAT
- Time on site
- 10–16 weeks on site
- Planning rules
- Wales
- Price level
- About 8% below the national guide
- Towns listed
- 4
- Survey
- Free, with a written quote
How much does a single-storey extension cost in South Glamorgan?
What should you budget for a single-storey extension in South Glamorgan? Use the figures below as a starting point. Prices in Wales sit about 8% below the national guide, so the range here is £32,000–£69,000 including VAT. Your fixed price comes in writing once we've surveyed the property, at no charge.
| Type of job | What it usually involves | Guide in South Glamorgan |
|---|---|---|
| Small extension (8–12m²) | A modest rear or side extension, such as a utility room or a slightly larger kitchen. | £20,000–£37,000 |
| Typical rear extension (15–25m²) | A kitchen-diner or family room with bifold doors and a rooflight or lantern. | £32,000–£69,000 |
| Large or wrap-around (30m² plus) | A wrap-around or wide rear extension, often with structural steelwork into the house. | £64,000–£120,000 |
Your price depends mostly on:
- Roof type, rooflights, lanterns and the amount of glazing
- Ground conditions, foundation depth and drains to divert
- Steelwork needed to open into the existing house
- Finishes, kitchen, flooring and heating specification
What’s included?
- Groundworks, foundations and below-ground drainage
- Cavity walls built and insulated to building regulations
- Steel beams to open into the existing house
- Electrics and plumbing by qualified trades, with certificates
- Plastering, screed floor and internal doors
- Building control inspections and completion certificate
Housing across South Glamorgan
Cardiff has large areas of bay-fronted Victorian and Edwardian terraces in districts such as Roath, Canton and Cathays, plus interwar suburbs, post-war estates and modern flats around Cardiff Bay. Penarth has Victorian villas, Barry mixes terraces with newer estates, and Vale of Glamorgan villages are often built of local limestone.
Terraces commonly suit loft conversions, side-return and rear extensions, and bay window renewal. Suburban semis take side extensions and driveways, and stone village homes need lime-based repairs.
Mild but wet, with coastal exposure along the Severn estuary and Bristol Channel affecting render, roofline and windows.
Planning and building rules in South Glamorgan
Which rules apply depends on where you live. For South Glamorgan, the answer is Wales, and the points below reflect that; we verify them with the council before quoting.
In Wales, permitted development allows many single-storey rear extensions, with depth and height limits that depend on the type of house and how close the extension comes to your boundaries. Side extensions, listed buildings, conservation areas and flats usually need planning permission.
Building Regulations in Wales apply to extensions, from foundations to insulation and fire safety. The Party Wall etc. Act 1996 applies in Wales as it does in England.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
From survey to handover
Survey and measure
We begin by looking at the job in person. During the free survey we discuss options, materials and budget for a single-storey extension, and photograph or measure anything the quote needs to reflect.
Your fixed price
The quote arrives in writing, not over the phone. It covers the full scope, the finishes you've chosen, any exclusions and the payment schedule, with a fixed price tied to that specification.
Dates and permissions
Preparation matters as much as the build. We agree access, parking and working hours with you, order materials in good time, and confirm any permissions so the job isn't held up once it starts.
Build and hand over
On site, the agreed plan is followed and any change is put in writing first. At completion we do a final clean, go through the snagging list with you and leave you with the relevant documents.
What you can expect from us
Questions about a single-storey extension in South Glamorgan
Do I need an architect for an extension?
You need proper drawings for an extension, but not always a full architect service. A designer or architectural technician can produce planning and building regulations drawings, and a structural engineer provides beam and foundation calculations. If you already have drawings, we price from them. If not, we can arrange the drawings and calculations as part of the project so everything is coordinated from the start.
Can we stay at home during the build?
Most people stay at home while we build a single-storey extension, because the new structure goes up outside before we break through. The disruptive part is usually the last few weeks, when we open into the house and fit the kitchen. We put up dust screens, keep a safe route through the house and agree a temporary kitchen setup if needed. Water and power are only off for short, planned periods.
How much will a single-storey extension cost in South Glamorgan?
As a guide, expect to pay £32,000–£69,000 including VAT for a single-storey extension in South Glamorgan. That range is adjusted for Wales, which runs about 8% below the national guide. Where your project lands depends on size, materials, access and the condition of what is already there. We confirm a fixed price in writing after a free survey of your home.
How long does a single-storey extension take to build?
A single-storey extension usually takes 10–16 weeks on site, from digging foundations to final plastering. Bad weather, deep foundations or a complex roof can add time. Before work starts, allow several weeks for drawings, structural calculations and building control approval, and longer if planning permission is needed. We give you a stage-by-stage programme with your quote so you know what happens each week.
Is the price fixed?
Yes, for the specification we agree. Your written quote sets out exactly what is included at a fixed price. It only changes if you ask for something different, or if a problem the survey could not reasonably reveal later needs extra work. In either case we explain the change and confirm it in writing before going ahead.
Towns in South Glamorgan
Looking for a single-storey extension somewhere in South Glamorgan? Start with the towns below; each links to a page with pricing for your region and coverage details.