England
- C3: family houses and up to 6 people living as one household.
- C4: 3–6 unrelated people sharing basic amenities.
- C3 to C4 is permitted development unless an Article 4 direction removes it. Article 4 directions are common in cities with many HMOs.
- 7 or more is sui generis and normally needs planning permission.
Wales
C4 exists, but permitted development only runs from C4 to C3. A change from a house to an HMO needs planning permission, and councils such as Cardiff apply concentration thresholds.
Scotland
There is no C4 class. Class 9 (houses) covers up to 5 residents living together, and councils set their own HMO planning policies.
Northern Ireland
All new HMOs need planning permission and building control approval. Belfast has applied HMO policy areas with limits on concentration.
Planning, licensing and building control are separate
Each is a separate decision. A licence does not grant planning permission, and planning permission does not mean building control approval.
Questions
What is an Article 4 direction?
A council direction removing a permitted development right, often the change from a family house to a small HMO.
Can I apply after converting?
Retrospective applications are possible but risky. Check before buying or starting work.
Does a lawful development certificate help?
It can confirm an existing lawful use. In Northern Ireland a certificate of lawful use may be possible after 5 years of continuous HMO use.
Checked 31 October 2026. General information for landlords planning works, not legal advice. Check the council’s pages for the exact address.