C3 to C4: when a house becomes a small HMO

The c3 to c4 boundary turns on numbers and household composition: class C4 covers a small house in multiple occupation shared by between three and six unrelated people who share basic amenities such as a kitchen or a bathroom. Below three, or where the occupiers form a single household, the property remains in class C3. Above six it leaves the class system altogether and becomes sui generis.

A national permitted development right allows movement between C3 and C4 in both directions. Whether it is available on your property is the first thing to check, because in a great many towns it has been removed.

What C4 covers and the occupier numbers

Class C3 covers dwellinghouses used by a single person or a family, and also by small groups living together as a single household, including certain care arrangements, up to six residents.

Class C4 covers small shared houses occupied by three to six unrelated individuals as their only or main residence, sharing one or more basic amenities. The sharing is what matters. A property converted into self-contained flats each with its own kitchen and bathroom is not a C4 house in multiple occupation, it is a set of separate C3 dwellings, and creating them is a different planning question with different consequences.

Seven or more occupiers takes the property outside both classes and into the territory of the uses that belong to no class at all, so a change to a large house in multiple occupation always requires planning permission.

The word unrelated is doing work here. A family of five with a lodger is not the same as five students on separate tenancies, and the assessment looks at how the household actually functions rather than at the tenancy paperwork alone.

The permitted development right between C3 and C4

Part 3 of Schedule 2 to the General Permitted Development Order permits a change of use from a dwellinghouse in C3 to a small house in multiple occupation in C4, and back again. That is a national right, so in most of the country converting a family house into a three to six person shared house needs no planning application.

Two caveats follow immediately. The right can be removed by a condition on a previous planning permission, which is common on new housing estates and on conversions, so check the planning history of the property rather than assuming. And it can be removed across an area by an Article 4 direction.

The reverse direction is worth knowing too. Where a property is lawfully in C4, the right to revert to C3 means the owner can return it to a family house without permission, which matters for an exit strategy.

Where an Article 4 direction removes it

Many authorities with large student or young professional populations have made Article 4 directions removing the C3 to C4 right, so that every new small house in multiple occupation needs planning permission. The direction is made by the council, applies to a defined area, and takes effect after the notice period.

National policy expects directions of this kind to be limited to situations where they are necessary to avoid wholly unacceptable harm and to cover the smallest area needed. In practice the areas covered are often substantial, and the boundaries are precise: a street on one side of a line is covered and the next street is not.

Check the direction itself rather than a summary. Look for the date it came into force, the exact area boundary, and what it removes, because some directions cover only the C3 to C4 change while others go wider. Where a property was already lawfully in C4 before the direction took effect, that lawful use is unaffected, and proving it becomes the whole game.

Evidence of the existing lawful use

Where a house has been shared for years, the value of the asset depends on being able to prove it. Assemble the evidence before you need it.

• Tenancy agreements for consecutive periods, showing the number of occupiers and that they were separate households.
• Council tax records and any student exemption certificates.
• Electoral roll entries.
• Any licence granted under the housing legislation, with its dates.
• Utility accounts, tenancy deposit registrations and letting agent records.
• Statutory declarations from previous tenants or the managing agent.

Then apply for a certificate of lawfulness of existing use or development under section 191 of the Town and Country Planning Act 1990. That is the only formal way to confirm that a use is lawful, and it converts a pile of paperwork into a document a lender, a purchaser and the council will all accept.

Do it while the evidence is fresh. Reconstructing occupancy from eight years ago after the letting agent has changed hands is a different exercise entirely.

Amenity standards councils apply

Where permission is required, the application is assessed against local plan policies and often a supplementary planning document on houses in multiple occupation. Recurring themes across authorities include the following.

Room sizes and the ratio of kitchens, bathrooms and living space to occupiers, which are usually set out in a local standard. Refuse and recycling storage, because bin presentation is the most visible neighbour issue and the one that generates complaints. Cycle parking, sound insulation between rooms and to adjoining properties, and the external appearance of the property including any loss of front garden to parking.

Parking is frequently the decisive issue, and the evidence councils accept is a survey rather than an assertion. A Parking Survey carried out to a recognised methodology, over the right nights and outside holiday periods, is what answers a highway objection.

Several councils also apply concentration policies, refusing a new house in multiple occupation where a stated proportion of nearby properties are already in that use. Those thresholds are local, so read the policy.

Licensing as a separate regime

Licensing sits under housing legislation and answers a different question from planning. Mandatory licensing applies to houses in multiple occupation occupied by five or more people forming two or more households, whatever the size of the property. Councils can also operate additional licensing schemes covering smaller houses in multiple occupation in defined areas.

Licence conditions cover management, safety and minimum sleeping room sizes, and the room size figures are set out in the licensing rules rather than in planning policy. Check the current figures with the council, because they are amended from time to time.

A licence does not authorise a change of use, and planning permission does not exempt anyone from licensing. Operating an unlicensed licensable property carries civil penalties and can trigger a rent repayment order, so the two need dealing with together rather than sequentially.

Recording the change for a future sale

Whatever route you took, create the paper trail now.

Keep the lawful development certificate, or the planning permission and its conditions, in the property file with the licence, the gas and electrical certificates and the tenancy history. Note any condition that restricts occupancy numbers, because a purchaser's solicitor will find it and a lender may ask about it.

Where the property was converted under permitted development, keep the evidence of the date the use began and the number of occupiers from the outset. That is the document that protects the value if an Article 4 direction is made later.

This is general guidance rather than legal advice, and the position depends on the planning history of the individual property and on any Article 4 direction in force, so check with your local planning authority 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. A Planning Statement setting out the existing lawful use and the evidence for it is the core document in most of these applications.