The three to six person boundary for a small HMO
Class C4 runs from three to six residents sharing amenities. Above that the use is sui generis, and inside an Article 4 area even the small change needs permission.
Class C4 of the Use Classes Order 1987 covers a dwellinghouse used by no more than six residents as a house in multiple occupation. The c4 hmo three to six people range comes from two sources read together: the lower end from the definition of a house in multiple occupation in the Housing Act 2004, which in practice needs three or more occupiers forming more than one household and sharing basic amenities, and the upper end from the words of Class C4 itself. Seven residents or more takes the property outside C4 altogether and makes it sui generis, needing planning permission in its own right.
Those two numbers decide whether you need an application. The licensing regime uses different numbers again, and conflating them is the mistake that costs landlords money.
What Class C4 covers and how occupancy is counted
Class C4 borrows the definition of a house in multiple occupation from section 254 of the Housing Act 2004, excluding converted blocks of flats dealt with under section 257. The standard test asks four questions: is the building occupied by persons forming more than one household, do they share basic amenities or does the accommodation lack them, does at least one occupier pay rent, and is it their only or main residence.
Counting residents means counting people, not bedrooms or tenancies. Six residents in five bedrooms is still six residents. A couple sharing a room are two residents, although they are one household, which matters for the household test but not for the headcount.
Children count. A household with a child occupying a room in a shared house adds to the total, which is a point that catches landlords who let on a per-room basis and never ask who else has moved in.
The practical consequence is that a six-person C4 house has no headroom. One extra occupier moving in, even informally, takes the use outside the class, and that is a breach of planning control rather than a technicality.
Sharing basic amenities as part of the definition
Sharing is as much part of the definition as the headcount, and it is where the boundary with self-contained flats sits.
Basic amenities means a toilet, personal washing facilities and cooking facilities. Occupiers who share any of those, or whose accommodation lacks them, fall within the standard test. Occupiers who each have their own self-contained unit, with their own kitchen and bathroom behind their own front door, do not: those are separate dwellings, which is a different change of use altogether and usually a more difficult application.
The in-between arrangement is the problem one. A house converted into bedrooms with en suite shower rooms but a single shared kitchen is still a house in multiple occupation, because the cooking facilities are shared. A house converted into studios each with a kitchenette and a shower room, sharing only a hallway, is probably several dwellings. Where a landlord has gone part way, the classification depends on the detail of what is shared, and the question of whether parts of a building form separate planning units runs the same way as it does for upper floors above a shop.
If you are unsure which side of the line a conversion falls, resolve it before you build the partitions, because unpicking it afterwards is expensive.
Families, lodgers and when C3 still applies
Class C3 covers use as a dwellinghouse by a single person or by people living together as a family, and by not more than six residents living together as a single household, with or without care.
Three common arrangements stay in C3.
- A family, however large, occupying the house as a single household.
- A resident owner or tenant with one or two lodgers, which the Order and the Housing Act treat as remaining a single household arrangement in most cases.
- A group who really do live together as a single household, such as a religious community or a small group home, rather than as separate households sharing a building.
The last of those is narrower than landlords hope. Four students on separate tenancies, each with their own room and a joint kitchen, are not a single household however friendly they are. The test looks at the legal and practical arrangements, not at whether they get on.
| Occupancy | Planning class | Application needed? |
|---|---|---|
| Family or single household, up to six | C3 | No |
| Three to six sharers, separate households, shared amenities | C4 | Only if an Article 4 direction applies |
| Seven or more sharers | Sui generis | Yes, always |
| Self-contained flats behind their own front doors | C3 units | Yes, change to multiple dwellings |
The permitted change from C3 to C4
Part 3 of Schedule 2 to the General Permitted Development Order 2015 permits a change of use from Class C3 to Class C4, and from Class C4 back to Class C3. No application is needed and no prior approval procedure applies.
That right is the foundation of small-scale HMO investment, and it is also the right most frequently removed. Note what it does not do. It does not permit a change to a large HMO of seven or more residents, it does not permit the creation of separate dwellings, and it does not authorise any operational development, so a rear extension, a dormer or a new bin store still stands or falls on its own.
The right also does nothing about the condition of the building. Fire safety duties, the Housing Health and Safety Rating System, minimum room sizes under licensing and Building Regulations where works are carried out all apply regardless.
Article 4 directions removing that change
Many authorities, particularly in university towns and cities with large private rented sectors, have made Article 4 directions withdrawing the permitted change from C3 to C4. Inside a direction area, converting a family house to a small HMO needs planning permission.
Check the direction itself rather than a summary. Directions vary in three ways that matter. The geographical extent, which may be a ward, a defined zone or the whole authority area. Whether the direction covers only the C3 to C4 change or other rights as well. And the date it took effect, since a use established before that date is unaffected.
Where permission is needed, the policy test is usually a concentration policy. Authorities commonly assess the proportion of existing HMOs within a stated radius or within a defined number of neighbouring properties, and refuse where a threshold is exceeded or where the proposal would sandwich a family dwelling between two HMOs. Read the policy and count the existing properties before you buy, using the authority's own licensing register where it publishes one.
Amenity standards, refuse storage and parking are the other three grounds. A Parking Survey carried out to a recognised methodology, with overnight counts midweek and at the weekend, is the evidence that answers a parking stress objection, and councils usually expect a suitably qualified author for that work.
Evidence of the lawful existing use
Buying a property described as an HMO is not the same as buying a lawful C4 use, and the burden of proving lawfulness falls on the owner.
Assemble the file before completion where you can: tenancy agreements over the relevant period, council tax records, electoral roll entries, utility accounts, any HMO licence and its application, rent records, and correspondence with the authority. Photographs of room layouts help where the configuration has changed.
Where a change of use happened without permission, immunity from enforcement depends on the passage of time. The Levelling-up and Regeneration Act 2023 moved England to a single ten-year time limit for enforcement action, which took effect in April 2024, with the earlier shorter limits continuing to apply to breaches that had already occurred by then. The position for a particular property therefore depends on when the breach began, and that is a question for advice rather than assumption.
A Lawful Development Certificate under section 191 of the Town and Country Planning Act 1990 is the only formal way to confirm that an existing use is lawful, and lenders increasingly ask for one on HMO purchases in Article 4 areas. A Planning Statement setting out the occupancy history with the evidence for each period is the core of that application.
Licensing is a separate regime
Planning and licensing are run by different teams, use different thresholds and answer different questions. Satisfying one tells you nothing about the other.
Mandatory licensing applies to houses in multiple occupation with five or more occupiers forming more than one household, regardless of the number of storeys. Many authorities operate additional licensing schemes that catch smaller HMOs, and selective licensing schemes that catch single-family lettings in designated areas. Licensing deals with management standards, room sizes, amenity provision and fire precautions.
So a five-person HMO in an Article 4 area needs planning permission and a mandatory licence. A four-person HMO outside an Article 4 area may need neither, or may need a licence under an additional scheme and no planning application at all. Check both registers for the specific address, and do not let a letting agent tell you that a licence makes the planning position safe.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Enter your postcode on PlanScope to see which documents an HMO application in your area is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Do children count towards the six resident limit?
Yes. Class C4 counts residents, not bedrooms or tenancies, so a child occupying a room in a shared house adds to the total. A couple sharing a room are two residents although they form one household. A six-person C4 house therefore has no headroom, and one extra occupier takes the use outside the class.
Is a house let to two sharers an HMO for planning purposes?
In practice no. The definition borrowed from the Housing Act 2004 is applied as needing three or more occupiers forming more than one household and sharing basic amenities. A dwelling let to two people is normally treated as remaining in Class C3, as is a resident owner with one or two lodgers.
What happens at seven residents?
The use falls outside Class C4 and becomes sui generis, so planning permission is required whether or not an Article 4 direction applies. There is no permitted development route from C4 to a large HMO, and the policy tests on concentration, amenity, refuse storage and parking all apply to the application.
How do I check whether an Article 4 direction applies?
Read the direction itself rather than a summary. Check its geographical extent, which may be a ward, a defined zone or the whole authority area, check whether it covers only the C3 to C4 change, and check the date it took effect, since a use lawfully established before that date is unaffected by it.
Does an HMO licence make the planning position lawful?
No. Licensing and planning are separate regimes with different thresholds. Mandatory licensing applies at five or more occupiers forming more than one household, and additional schemes catch smaller properties. A licence addresses management standards and fire precautions, and says nothing about whether the use is lawful in planning terms.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.