Change of use to C4: the HMO threshold explained

Class C4 of the Use Classes Order covers a small house in multiple occupation, meaning a dwelling occupied by three to six unrelated people who share a kitchen, bathroom or toilet and live there as their only or main residence. Below three occupiers the property stays in Class C3. Above six it leaves the use classes altogether and becomes sui generis, which means a full planning application whatever the local policy says.

The c4 use class hmo boundary matters because it decides whether you need permission at all, and the answer changes street by street depending on whether an Article 4 direction is in force.

What C3, C4 and large HMOs cover

Class C3 is a dwellinghouse. It covers a single person or a family, and it also covers up to six people living together as a single household, including care arrangements and religious communities. The phrase doing the work is single household, which the Housing Act 2004 defines by reference to family relationships rather than to a shared tenancy agreement.

Class C4 covers the same building occupied by three to six people who are not a single household and who share basic amenities. The definition is borrowed from section 254 of the Housing Act 2004, so the planning class and the housing law test line up at this point, which they do not always do further up the scale.

Seven or more occupiers takes the property outside both classes. A large HMO is sui generis, there is no permitted development route into it, and it is assessed on its merits against the development plan every time.

Where the three to six line comes from

The counting is of people, not of bedrooms or tenancies. Six adults in six letting rooms is C4. Seven adults in six rooms, where one room is shared by a couple who are not part of any wider household, takes the property into sui generis territory even though nothing has been built.

Two consequences follow, and both catch investors out.

The first is that a permission for C4 use does not authorise seven occupants. Councils increasingly attach a condition capping the number of occupiers, and where they do not, the use class itself does the capping. Letting a seventh room is a material change of use and enforcement can follow.

The second is that the change is about use rather than works. Internal alterations to create letting rooms are not usually development at all, which our explainer on what section 55 actually means by development sets out. The planning issue is created by who lives there and how, and that assessment follows the ordinary material change of use test described in our note on the test councils apply.

Class L permitted development between C3 and C4

Class L of Part 3 of Schedule 2 to the General Permitted Development Order 2015 permits a change of use from Class C3 to Class C4, and back again from C4 to C3. No application and no fee, and no prior approval stage either.

That right is what makes the small HMO model work in most of the country. It is also the right that councils remove most often.

Where Class L survives, the sensible step before letting is a lawful development certificate for the proposed use. It costs half the equivalent planning fee, takes eight weeks, and produces a document a mortgage lender and a future buyer will both want to see. Where the property has been in C4 use for a long time without any certificate, an existing-use certificate does the same job retrospectively.

Where an Article 4 direction removes the change

An Article 4 direction withdrawing Class L is common in university towns, around large hospitals and in parts of many cities with concentrated private renting. Inside the direction area, moving from C3 to C4 needs a planning application, judged against the local plan's HMO policies.

Those policies usually work on concentration. The council counts existing HMOs within a defined radius of the application property, often using council tax and licensing records, and refuses where the proportion exceeds a threshold set in the plan or in a supplementary planning document. Read the policy and do the count yourself before you buy, because the threshold is the whole decision on most of these applications.

No planning fee is payable where the application is needed only because of the direction. That is a small consolation, given that the direction has removed the fallback position that underpinned the purchase price.

Directions vary in scope. Some cover a single ward, some a whole borough, and some catch only certain streets. The direction schedule, rather than a summary map, is the document to read.

Licensing is a separate consent

A licence under the Housing Act 2004 is not planning permission, and planning permission is not a licence. You may need both, one, or neither, and holding one is no defence to enforcement under the other.

Mandatory licensing applies to any HMO occupied by five or more people forming two or more households, regardless of the number of storeys. Many councils operate additional licensing for smaller HMOs and selective licensing for other private rented housing, each under its own scheme with its own boundary.

Licensing brings national minimum room sizes with it. Under the mandatory conditions regulations, a room used for sleeping by one person over ten years old must be at least 6.51 m², a room for two adults at least 10.22 m², and a room for a child under ten at least 4.64 m². Rooms below 4.64 m² cannot be used for sleeping at all. Those figures are licensing standards rather than planning policy, but they shape the layout, and a planning application showing rooms that could never be licensed invites a refusal on living conditions.

What councils ask for on amenity and bin storage

Where an application is needed, the supporting material is short but specific.

• Existing and proposed floor plans with every room dimensioned and labelled by intended occupancy.
• A schedule of shared kitchen, bathroom and WC provision against the number of occupiers, measured against the council's own HMO amenity standards.
• Refuse and recycling storage sized for the occupancy, shown in a position the collection crew can reach, with a screened enclosure at the front where there is no rear access.
• Cycle parking, usually secure and covered.
• A parking stress survey where the local plan applies a parking standard to HMOs, which a Parking Survey sets out using an overnight beat count on the surrounding streets.
• A short management statement covering the letting arrangement, waste, noise and the responsible manager.

Bin storage is the item that generates the most objections and the fewest pages of evidence. On a terraced street with no rear access, six occupiers producing individually bagged waste in a small front garden is exactly the harm the concentration policies were written to address, and a designed enclosure answers it better than an assurance.

Before committing to a purchase, check the direction position, the concentration policy and the licensing scheme in that order. You can also enter the postcode on PlanScope to see which constraints are recorded against the property. This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.