C4 house in multiple occupation or sui generis HMO

The line between a C4 HMO and a sui generis HMO is the sixth occupier. Class C4 of the Use Classes Order covers a house in multiple occupation shared by no more than six residents. Add a seventh and the property leaves the class system altogether, becomes sui generis, and needs planning permission for the change in every part of the country, article 4 direction or not.

That single number drives a lot of acquisition decisions. It also explains why so many student lettings stop at six bedrooms when the building could comfortably hold eight.

The three to six occupier definition

Class C4 was inserted into the Town and Country Planning (Use Classes) Order 1987 in 2010. It covers the use of a dwellinghouse by not more than six residents as a house in multiple occupation within the meaning of section 254 of the Housing Act 2004, excluding the converted blocks of flats caught by section 257 of that Act.

The section 254 definition is the one doing the work. Broadly, a property is an HMO where it is occupied by persons forming more than one household as their only or main residence, and those occupiers share a basic amenity such as a kitchen, bathroom or toilet. Two sharers is generally still C3, because C3 covers use by up to six residents living together as a single household and also by small groups in certain care arrangements. Three unrelated sharers is where most councils treat C4 as engaged.

Household matters as much as headcount. A couple counts as one household, so a house with a couple and four individual sharers has five households and six residents, which still sits inside C4.

Where a large HMO becomes sui generis

Seven or more residents takes the property outside C4. There is no class for a large HMO, so it is sui generis, and any change into it needs a full planning application judged on its merits.

The practical consequences for an investor are worth setting out plainly:

• No permitted change applies, so permission is required even where the property is already a lawful C4 HMO
• The application is determined against local plan policy on HMO concentration, amenity and parking rather than against a prior approval checklist
• A refusal is appealable, but the appeal turns on planning merits rather than on a procedural test
• Conditions restricting occupancy are common, and our note on conditions that tie a use to one class or occupier explains how tightly they can bite

Counting is done on residents rather than bedrooms. A six bedroom house let to six students is C4. The same house let to six students and a live-in couple is not.

The permitted change between C3 and C4

Part 3 of Schedule 2 to the General Permitted Development Order 2015 permits change of use from C3 to C4, and from C4 back to C3. That right is what makes small HMO conversion viable in most of England without a planning application.

The right is subject to the usual limitations. It does not apply where an article 4 direction has withdrawn it, it does not authorise building operations, and it does not override a condition on an earlier permission that restricts the use of the property. A house built under a permission conditioned to C3 occupation only cannot rely on the class.

Physical works are a separate question. Adding an en suite, forming a dormer or building a rear extension may need permission or prior approval in its own right, and a conversion delivered entirely within permitted development for both use and works is rarer than it sounds.

Article 4 directions in university towns

Councils in cities with large student populations have made article 4 directions removing the C3 to C4 right, sometimes across the whole authority area and sometimes in defined wards. Inside a direction area, a change from a family house to a small HMO needs planning permission.

Directions are local instruments with local wording. Read the direction itself and its map rather than a summary on a council web page, because the boundary can follow a street line in a way a summary will not capture. Check the date it came into force too, since a use established before that date may be lawful.

Where a direction applies, councils generally assess applications against a concentration policy. These are usually expressed as a proportion of HMOs within a stated radius of the application property, with the percentage and the radius both set locally in the local plan or a supplementary planning document. Some authorities also apply a sandwiching test that refuses an HMO between two family dwellings. Get the council's own published policy and its HMO register before you exchange contracts.

Licensing as a separate regime

Planning permission and HMO licensing are different consents from different statutes, decided by different teams. Mandatory licensing under Part 2 of the Housing Act 2004 applies to an HMO occupied by five or more persons forming two or more households, regardless of how many storeys the building has. Councils may also run additional licensing schemes covering smaller HMOs and selective licensing covering all private rented housing in a designated area.

A licence is not evidence of planning lawfulness, and a planning permission does not guarantee a licence. Buyers routinely assume that a licensed HMO must be lawful in planning terms, and that assumption has produced a great many enforcement cases.

Mandatory licence conditions set minimum room sizes: 6.51 m² for a room occupied by one person over ten years old, 10.22 m² for two persons, and 4.64 m² for a child under ten. Those figures come from the 2018 mandatory conditions regulations and they are a licensing standard rather than a planning standard, though officers often refer to them when assessing amenity.

Amenity, bin storage and parking evidence

The evidence pack for an HMO application is short but specific. Councils want to see internal room sizes and communal space on the floor plans, a bin and recycling store sized for the number of occupiers and within a sensible carrying distance of the collection point, secure cycle parking, and usable private or shared outdoor amenity space.

Parking is where most refusals originate. Where the council's standard would generate more demand than the street can absorb, a Parking Survey carried out to the Lambeth methodology, with overnight counts on a midweek night and a weekend night outside school holidays, is the evidence that answers the highway officer. A survey taken in August tells nobody anything about a student street.

Noise and refuse management plans are worth submitting voluntarily for larger schemes. They cost little and they take two common objection themes off the table. Our guide to the evidence pack for a change of use application covers the general structure.

Applying for seven or more occupiers

For a sui generis HMO application, assemble the pack in this order:

1. Confirm the lawful existing use, with evidence if the property has been an HMO for some years.
2. Check for article 4 directions, conditions on earlier permissions and any licensing designation.
3. Prepare floor plans showing room areas, communal space and storage.
4. Commission a parking survey if the council's standard is not met on site.
5. Draft a Planning Statement addressing concentration policy, amenity, parking, refuse and management.
6. Submit, and expect a consultation response from the licensing team as well as from neighbours.

An illustrative case: a four storey Victorian terrace, currently a lawful six person C4 HMO, proposed for nine bedrooms. That is a sui generis application. The concentration policy, the bin store and the parking survey will decide it, and the licensing team will want the room sizes to meet the mandatory conditions before a licence is issued.

Enter your postcode on PlanScope to see which reports an HMO conversion at your address is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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