HMO conversion in Cardiff: Use Class C4, licensing, and what's different locally

A different legal mechanism from England's Article 4

Cardiff's HMO planning control does not work like Article 4 in English cities. Since 25 February 2016, a Wales-wide Use Class C4 order has required planning permission for HMO conversion across the whole of Cardiff, covering both C4 HMOs of three to six occupants and larger sui generis HMOs of seven or more, effectively citywide rather than discretionary or area-specific in the way an English council's Article 4 direction is. Within that, density thresholds add a further layer: a conversion is likely to be refused if it would take dwelling density above 20% within a 50 metre radius in Cathays and Plasnewydd specifically, or above 10% elsewhere in the city.

Rent Smart Wales adds a compliance layer with no English equivalent

Every landlord in Wales, not just HMO landlords, must register with Rent Smart Wales (£37 for five years) and either hold a personal licence or use a licensed agent, a nationwide compliance requirement with no direct equivalent in England. On top of that, Cardiff runs additional licensing in Cathays, currently designated from 1 February 2023 for five years, running to around February 2028. The Plasnewydd additional licensing scheme ran from 1 January 2021 to 31 December 2025 and had expired by the end of 2025 at time of writing; its renewal status should be checked directly with the council before relying on it. Cardiff does not currently run selective licensing.

Strong demand against a genuine student housing shortfall

Cardiff has around 46,600 students but only about 16,100 purpose-built student beds, a meaningful supply gap that continues to drive HMO demand. Wales-wide, HMO yields are the highest of any UK nation, averaging 9.01% gross per Paragon Bank data, and high-spec HMOs in CF24 (Roath, Cathays) are commonly cited around 8.9% gross.

For the national planning and licensing rules this local guide builds on, see the UK HMO conversion guide. For Cardiff-specific price and yield numbers relevant to a conversion project, see BRR in Cardiff, and for sourcing conversion candidates through auction, see buying property at auction in Cardiff.

Common questions

Does Article 4 apply to HMO conversion in Cardiff?

Not in the English sense. Since 25 February 2016, a Wales-wide Use Class C4 order has required planning permission for HMO conversion across the whole of Cardiff, both for C4 HMOs of three to six occupants and larger sui generis HMOs, effectively citywide rather than area-specific.

What is Rent Smart Wales and does it apply to Cardiff landlords?

Yes. Every landlord in Wales must register with Rent Smart Wales (£37 for five years) and either hold a personal licence or use a licensed agent, a nationwide requirement with no direct equivalent in England, on top of any HMO-specific licensing.

Does Cardiff have selective licensing like other cities in this guide?

No. Cardiff does not currently run selective licensing, unlike Bristol, Sheffield, Nottingham and Newcastle; it does run additional licensing in Cathays, designated from 1 February 2023 for five years, while the Plasnewydd additional licensing scheme expired at the end of 2025 and its renewal status should be checked with the council.

Planning and licensing details for Cardiff verified against multiple local and Welsh Government sources (council pages and specialist property-compliance sites), August 2026. This is general information, not legal or planning advice; always confirm current status with the relevant local authority for the specific address.