Two-storey annexe 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: Can be permitted development in Wales if it is 10.5 m from the side boundary, set back 1 m from the front and doesn't widen the house by more than half; otherwise planning permission.
Site visits: Free, no obligation

What a two-storey annexe extension involves

This service suits you if a parent, grown-up child or carer is moving in and you want them to have their own space while staying connected to the house. You get a layout that can be self-contained or shared, the approvals your nation needs with the annexe use made clear, accessible design where needed and the build, carried out by vetted teams working under S&K.

Across Cardiff and the Vale of Glamorgan we cover Cardiff (CF10), Barry (CF62), Penarth (CF64), Llantwit Major (CF61), Whitchurch (Cardiff and the Vale of Glamorgan) (CF14) and Rhiwbina (CF14), plus the smaller places around them.

Guide price in Wales

Expect a two-storey annexe extension in Cardiff and the Vale of Glamorgan to land somewhere around £79,000–£106,500 (plus kitchenette and shower room fittings, priced to your choice) for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Our Wales guide rate is £1,890–£2,530 per m², including VAT. 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	Typical project
Essential	£1,740–£2,330 per m²	£73,000–£98,000
Standard	£1,890–£2,530 per m²	£79,000–£106,500
Premium	£2,260–£3,040 per m²	£95,000–£127,500

Rules in Wales

In Wales, a two-storey annexe extension can use the same permitted development rules as other extensions: 4 m ground floor and 3 m first floor at the rear, or the 10.5 m, 1 m set-back and 50% width tests at the side. If you apply, the householder fee is £585, and councils may limit the annexe to use by the household.

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

Services and metering

An annexe usually shares the main house's water, gas and electricity, with a separate circuit or sub-meter if you want to split costs. We plan heating, hot water and drainage so the annexe works well without needing new supplies.

Annexe, not a separate house

To stay an annexe, the space should be used by members of the household and stay linked to the main house, usually with an internal door and shared address, garden and services. Designing it as a fully separate home can mean the council treats it as a new dwelling.

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.
Drawings, then consent
We draw the scheme, check it against the rules in Wales, and take it through the right consent with the council.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.

Towns we cover in Cardiff and the Vale of Glamorgan

Two-storey annexe extensions in Cardiff and the Vale of Glamorgan: questions

How much does a two-storey annexe extension cost in Cardiff and the Vale of Glamorgan?

In Wales our guide is £1,890–£2,530 per m² including VAT, so about £79,000–£106,500 (plus kitchenette and shower room fittings, priced to your choice) for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.

Can I rent out an annexe later?

Not always. Many annexe permissions include a condition that it is only used by members of the household, so renting it out may need a fresh planning application. If you think you might want to let it, tell us at the start so we can explain the options.

Can an annexe have its own front door?

It can, but a separate front door, kitchen and address together make it look more like a separate home, which can change how the council treats it for planning. Many annexes have their own door to the garden or side and an internal door to the main house. We explain how each choice is likely to be viewed before the design is fixed.

Can an annexe be designed for someone with limited mobility?

Yes. We can plan a ground-floor bedroom space, a level-access shower, wider doorways, lever handles and space for a stairlift later. These features are much cheaper to build in at the start than to add afterwards, and they keep the annexe useful as needs change.

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

Cardiff and the Vale of Glamorgan is in Wales. Can be permitted development in Wales if it is 10.5 m from the side boundary, set back 1 m from the front and doesn't widen the house by more than half; otherwise planning permission.

Neighbouring areas

All extension services in Cardiff and the Vale of Glamorgan · About two-storey annexe extensions