Extra bedroom and en-suite extensions in Cardiff and the Vale of Glamorgan

Cardiff and the Vale of Glamorgan at a glance

Nation: Wales
Price region: Wales
Postcode areas: CF
Towns covered: 10 listed below, plus surrounding villages
Approval route: It may be permitted development if the ground floor goes no more than 4 m and the first floor no more than 3 m beyond the original rear wall, with the first floor 10.5 m from the rear boundary.
Site visits: Free, no obligation

What an extra bedroom and en-suite extension involves

An extra bedroom and en-suite extension is a two-storey extension planned around a new double bedroom with its own shower room on the first floor, with a ground-floor room below. It is one of the most effective ways to add space for a growing family. Nationwide's 2025 research linked adding a double bedroom and bathroom to a three-bed, one-bathroom house with value gains of up to 24%.

Cardiff and the Vale of Glamorgan towns we list: Cardiff (CF10), Barry (CF62), Penarth (CF64), Llantwit Major (CF61), Whitchurch (Cardiff and the Vale of Glamorgan) (CF14) and Rhiwbina (CF14). Every other address in Cardiff and the Vale of Glamorgan is covered as well.

Guide price in Wales

In Wales, which includes Cardiff and the Vale of Glamorgan, we'd expect an extra bedroom and en-suite extension to cost around £51,500–£69,500 (plus £5,500–£11,000 for the en-suite) for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), or £1,840–£2,480 per m² including VAT. Professional fees for drawings and the structural engineer are listed separately on our prices page.

Spec	Per m²	Typical project
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

Rules in Wales

In Wales, an extra bedroom at the rear can be permitted development if the first floor goes no more than 3 m beyond the original rear wall and stays 10.5 m from the rear boundary. A two-storey side extension can also qualify 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).

The Party Wall etc. Act 1996 applies in Wales, so notices may be needed for work on or near a shared wall or boundary.

Getting the design right

Planning the en-suite

An en-suite needs a route for the soil pipe to the drains, enough fall for waste water and an extract fan to the outside under Part F. Placing it over the ground-floor utility or near an existing drain keeps pipework short and hidden.

Escape window and fire safety

A new first-floor bedroom needs an escape window with a clear opening of at least 0.33 m², at least 450 mm wide and high, and the bottom no more than 1,100 mm above the floor, unless there is a protected route to the stairs. We design the windows to meet this.

How we work in Cardiff and the Vale of Glamorgan

Understand the brief
At your home in Cardiff and the Vale of Glamorgan we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
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.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Towns we cover in Cardiff and the Vale of Glamorgan

Extra bedroom and en-suite extensions in Cardiff and the Vale of Glamorgan: questions

How much does an extra bedroom and en-suite extension cost in Cardiff and the Vale of Glamorgan?

In Wales our guide is £1,840–£2,480 per m² including VAT, so about £51,500–£69,500 (plus £5,500–£11,000 for the en-suite) for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.

What goes on the ground floor below a new bedroom?

Whatever suits you: a bigger kitchen, a family room, a study, a utility or a downstairs shower room. The ground floor usually costs about the same whatever it is used for, apart from kitchen units and bathroom fittings, which are priced separately.

How big should a new double bedroom be?

There is no legal minimum size for a bedroom in a house you own, so the test is whether it works. A comfortable double needs room for the bed with space to walk round it, wardrobes and a door that opens freely. We draw furniture on the plans so you can judge the space before anything is built.

Does an extra bedroom add value to my house?

It usually does, though not always by the full cost. Nationwide's 2025 research found that adding a double bedroom to a two-bed house was linked to about 13% higher value, and a double bedroom and bathroom on a three-bed, one-bathroom house up to 24%. Local ceiling prices still apply.

Will I need planning permission in Cardiff and the Vale of Glamorgan?

Cardiff and the Vale of Glamorgan is in Wales. It may be permitted development if the ground floor goes no more than 4 m and the first floor no more than 3 m beyond the original rear wall, with the first floor 10.5 m from the rear boundary.

Neighbouring areas

All extension services in Cardiff and the Vale of Glamorgan · About extra bedroom and en-suite extensions