Two-storey extensions for semi-detached houses in Whitchurch (Cardiff and the Vale of Glamorgan)

Useful details for planning a two-storey extension for a semi-detached house in Whitchurch (Cardiff and the Vale of Glamorgan).

Postcode districts: CF14
County / area: Cardiff and the Vale of Glamorgan, Wales
Price region: Wales
Guide price: £51,500–£69,500 (£1,840–£2,480 per m²)
Approval route: Depends on position: rear (3 m first floor, 10.5 m to the boundary) and some side extensions (10.5 m, 1 m set-back) can be permitted development in Wales.
Nearest towns: Rhiwbina (1.2 miles), Llandaff (1.3 miles), Thornhill (2.4 miles)
Distance to Cardiff: about 2.8 miles
First visit: Free, no obligation

About a two-storey extension for a semi-detached house

This service suits you if you own a semi-detached house and want to add bedrooms and living space without moving. On a semi, the main questions are which side to build on and how to treat the attached neighbour. You get a survey, design options, the approvals your nation needs and the build, carried out by vetted teams working under S&K.

We cover postcode district CF14 in and around Whitchurch (Cardiff and the Vale of Glamorgan), along with neighbouring Rhiwbina, Llandaff and Thornhill.

What it costs in Whitchurch (Cardiff and the Vale of Glamorgan)

Guide prices for two-storey extensions for semi-detached houses in Wales are around £1,840–£2,480 per m² of new floor space, including VAT. For a typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), that's roughly £51,500–£69,500. Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	A 4 m × 3.5 m footprint on two floors (28 m² of new floor space)
Essential	£1,690–£2,290 per m²	£47,500–£64,000
Standard	£1,840–£2,480 per m²	£51,500–£69,500
Premium	£2,210–£2,980 per m²	£62,000–£83,500

Planning and building regulations in Whitchurch (Cardiff and the Vale of Glamorgan)

In Wales, a semi can take a two-storey rear extension under permitted development with the ground floor up to 4 m and the first floor up to 3 m beyond the original rear wall, 10.5 m from the rear boundary. A side extension can also be permitted development if it is 10.5 m from the side boundary, set back 1 m and adds no more than 50% width. Otherwise the fee is £585.

Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.

Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).

Design points for Whitchurch (Cardiff and the Vale of Glamorgan) homes

Rear, side or both

On a semi, a rear extension sits against the attached neighbour, while a side extension faces the detached neighbour and the street. We compare the space, cost and approval route for each, and for a wraparound, before you commit to one design.

Keeping the pair balanced

Semis are designed as matching pairs, and a side extension changes that balance. Setting the side extension back from the front wall and keeping its ridge lower helps the pair still read as a pair, which councils' design guides commonly ask for.

How we'd run your project

Visit and first ideas
One of our team visits your house in Whitchurch (Cardiff and the Vale of Glamorgan), checks the walls, roof and drains, and sketches out options with you.
Design and approvals
We draw the extension and check it against the rules for Wales, then apply for planning permission or a certificate of lawfulness, whichever fits.
Structure and building control
A structural engineer sizes the foundations and steels, and we get building regulations approval before work starts.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about two-storey extensions for semi-detached houses in Whitchurch (Cardiff and the Vale of Glamorgan)

How much does a two-storey extension for a semi-detached house cost in Whitchurch (Cardiff and the Vale of Glamorgan)?

Our guide for Wales, which covers Whitchurch (Cardiff and the Vale of Glamorgan), is £1,840–£2,480 per m² including VAT. A typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space) comes to about £51,500–£69,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Which postcodes do you cover around Whitchurch (Cardiff and the Vale of Glamorgan)?

We cover Whitchurch (Cardiff and the Vale of Glamorgan) (CF14) and nearby places including Rhiwbina, Llandaff and Thornhill, plus the rest of Cardiff and the Vale of Glamorgan. The first site visit is free.

How long does a two-storey extension for a semi-detached house take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils normally decide householder applications within 8 weeks), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.

Will a side extension make my semi look like a terrace?

It can if it fills the whole gap to the boundary at first floor and the neighbour does the same. Many councils ask for a first-floor gap to the side boundary or a set-back for this reason. We design the extension to keep the semi reading as one of a pair.

Does a two-storey extension add value to a semi-detached house?

It usually adds value, but the gain is never certain. Nationwide's 2025 research found that 10% more floor area was linked to about 5% higher value, and that adding a double bedroom and bathroom to a three-bed, one-bathroom house could add up to 24%. Every street has a ceiling price, so check local sales first.

Nearby

Nearby towns we cover for two-storey extensions for semi-detached houses:

Other extensions in Whitchurch (Cardiff and the Vale of Glamorgan)

All two-storey extension services in Whitchurch (Cardiff and the Vale of Glamorgan) · Two-storey extensions for semi-detached houses across Cardiff and the Vale of Glamorgan

The quickest next step is a visit. We'll look at your house in Whitchurch (Cardiff and the Vale of Glamorgan) and give you an honest view of the options.