HMO extensions across Cardiff | HMO Refurbishment

In short: An HMO extension adds space to a shared house, usually a ground-floor bedroom with ensuite or a bigger communal kitchen. We carry this out across Cardiff, priced against the HMO rules for Wales and the council’s own standards.

Nation: Wales
Pricing region: Wales
Postcode areas: CF
Main towns: Cardiff, Whitchurch

What do extensions for extra rooms in Cardiff involve?

Building control completion
Planning route check and drawings
Party wall coordination where needed
Fire separation and detection extended to the new space
Kitchen or bedroom fit-out
Ensuite drainage and extraction

Which rules apply in Cardiff?

3–6 sharers is use class C4, and in Wales changing a house to C4 always needs planning permission; only C4 back to C3 is permitted development.
Building regulations cover structural work, partitions, drainage, fire-resisting construction and electrics; confirm with building control whether the conversion is a material change of use.
Fitness for human habitation rules require mains-powered, interlinked smoke alarms on every storey and CO alarms where there is a gas, oil or solid-fuel appliance.
Kitchen and bathroom ratios are set in each council’s HMO standards.
More than 6 sharers is a sui generis HMO and needs planning permission; councils such as Cardiff apply concentration limits.

Cardiff Council: local HMO schemes

Additional licensing	In force in part of the council area Cathays: 1 Feb 2023 to 1 Feb 2028. Plasnewydd had a scheme from 1 Jan 2021; check with Cardiff Council whether it has been renewed.
Selective licensing	No scheme found

Schemes change. Check the council’s current pages for the exact address in Cardiff before you buy or start work. Source: Cardiff Council HMO licensing page, checked 2026-10-31.

How much do extensions for extra rooms cost in Cardiff?

Regional adjustment for Wales. Planning budgets: see our prices page.
Item	UK typical	Local guide	Per
Single-storey extension, about 15 m²	£35,000 – £60,000	£32,900 – £56,400	project
Single-storey extension per m²	£1,800 – £4,000	£1,700 – £3,750	m²

Typical time on site: 8–14 weeks. For a figure for your house, try the guide-price tool.

Extensions for extra rooms by town in Cardiff

Questions about extensions for extra rooms in Cardiff

Will the extension affect neighbours?

Possibly, if it is on or near a boundary. Party wall procedures may apply in England and Wales.

Can I extend an HMO under permitted development?

Some extensions to houses are permitted development, but rules differ for HMOs and by nation and council. We check the address before design.

Do you carry out extensions for extra rooms across Cardiff?

Yes, across the whole of Cardiff, including Cardiff, Whitchurch.

Who licenses HMOs in Cardiff?

Cardiff council licenses HMOs in its area. Landlords must also register with Rent Smart Wales.

Extensions for extra rooms across Cardiff