When an HMO becomes sui generis at seven occupants

A seven occupant HMO needs planning permission, full stop. Class C4 of the Use Classes Order covers the use of a dwellinghouse by not more than six residents as a house in multiple occupation, so the seventh occupant takes the property out of the class and into sui generis, where no use class and no permitted change route applies. There is no prior approval, no notification and no threshold argument to be had. A landlord adding a seventh bedroom to a licensed six bed HMO is making a material change of use.

What follows is the part that costs money: once the use is outside the classes, the authority assesses it as a full application against its own HMO policies, and those policies are usually where the scheme fails rather than on the principle.

The six occupant ceiling in Class C4

Class C4 is defined by reference to the statutory definition of a house in multiple occupation in the Housing Act 2004, with the limit set at six residents. In practice that means three to six unrelated people sharing a kitchen or bathroom, living as more than one household.

Below three occupants the use normally remains Class C3, as a single household or as a household plus a lodger. Between three and six it is Class C4. Above six it is sui generis.

The change from C3 to C4 is permitted development under Part 3 of the General Permitted Development Order, in both directions, unless an Article 4 direction has removed the right. Many university towns and cities have made those directions, and in those areas even a four bed HMO needs permission. Check the authority's Article 4 register first, because the answer differs street by street in some boroughs.

What leaving the classes removes

Sui generis status takes away three things landlords tend to assume they have.

Flexibility. There is no class to move within, so any later change of use needs a fresh application, including going back to a six person HMO or to a single family house.

Permitted development. The rights in Part 3 are written as movements between named classes, and a sui generis use is outside all of them. The C3 to C4 route cannot be used to get to seven occupants in stages.

Certainty. A C4 conversion in an area without an Article 4 direction is lawful without anyone's permission. A large HMO is lawful only if the authority grants it, and plenty of authorities have policies that restrict HMO concentrations by area, often through a threshold on the proportion of HMOs within a defined radius.

What a full application has to address

Write the application around the authority's own HMO policy and its supplementary guidance, because that is what the officer will apply.

Expect to deal with concentration first. Many councils operate a test on the percentage of properties within a stated radius already in HMO use, sometimes with a sandwiching rule preventing an HMO immediately between two others. The evidence is usually drawn from the council's licensing register and council tax records, and the officer will run the figures whether or not you do. Run them yourself and present them.

Then amenity: room sizes, communal space, kitchen and bathroom provision, natural light and ventilation, noise transmission between rooms, and the effect on neighbours. Then highways and parking. Then refuse and cycle storage. Then management.

A planning statement is the right vehicle for the policy case, and it should set out the concentration arithmetic, the amenity schedule room by room and the management arrangements. Where the property is in a conservation area or is listed, the external alterations raise separate issues that need their own assessment.

Room sizes and the licensing overlap

Two regimes apply and they are not the same. Planning deals with the acceptability of the use. Licensing deals with the standard of the accommodation.

Mandatory HMO licensing applies to houses in multiple occupation occupied by five or more persons forming two or more households, following the removal of the storey threshold in 2018. Licence conditions include prescribed minimum sleeping room floor areas: 6.51 square metres for one person over ten years old, 10.22 square metres where two people over ten share, and 4.64 square metres for a child under ten. Additional licensing schemes in some areas catch smaller properties.

Many authorities also publish their own HMO amenity standards covering bathroom and kitchen ratios per occupant, communal living space and storage. Those are planning standards as well as licensing ones in several boroughs, and a room that satisfies the licensing minimum can still be refused on planning amenity grounds.

The point to hold on to is that a licence does not make the use lawful in planning terms, and planning permission does not guarantee a licence. Applications that assume one follows the other get into trouble at both ends.

Parking stress evidence

Large HMOs generate more car ownership per dwelling than a family house in some locations and less in others, and authorities almost always ask for evidence rather than assertion.

The conventional method is a parking stress survey following the approach developed in London and now used widely: a survey of available kerbside capacity and occupied spaces within a defined walking distance of the site, carried out overnight and at a weekend, avoiding school and public holidays, repeated on at least two occasions. Stress above roughly 85 per cent of capacity is generally treated as saturation, and a proposal adding demand to a saturated street has to answer for it.

Commission the parking survey properly or not at all. A single weekday afternoon count will be dismissed, and a survey with the radius drawn to include a quiet side street will be noticed. Where the site is well served by public transport, the argument shifts to accessibility and to a car free or car capped proposal, and the transport statement should make that case explicitly rather than leaving the officer to infer it.

Offer the mitigation that fits: a car free condition with no parking permits issued, secure cycle parking at a stated ratio, and a travel information pack for tenants.

Refuse, cycle storage and management

Refuse is the issue most often raised by neighbours and most often underdesigned by applicants.

Seven or more occupants generate more waste than the standard household collection assumes, and bins stored at the front of a terraced house are a visual and amenity problem the officer will not ignore. Show the bin numbers from the council's own waste standards, the storage location on a plan, the screening, and the route by which bins reach the collection point. Do the same for cycle parking, with stands rather than a bare shed floor.

Management is the last piece and the easiest to offer. A management plan covering the letting arrangement, the nominated manager, response times to complaints, refuse arrangements, noise rules and tenancy conditions costs nothing to draft and addresses the objection that no one is responsible when something goes wrong. Several authorities require one by condition anyway.

Residential class boundaries generate more argument than almost anything else in the Order, and the same pattern appears at the C2 to C3 boundary in retirement housing.

Conditions capping occupancy

Expect a condition limiting the maximum number of occupants, and read it carefully, because it defines the asset.

Conditions are commonly drafted by reference to a maximum number of residents, sometimes with a plan showing the approved room layout and a restriction on creating additional bedrooms. Where the permission is for a stated number, exceeding it is a breach of condition, enforceable without any argument about use classes.

Two further conditions are common. A requirement that the refuse and cycle storage shown on the approved plan is provided before occupation and retained. And a requirement to submit and comply with a management plan.

An illustrative example. A six bed licensed HMO in a street with no Article 4 direction converts a dining room into a seventh bedroom. The use becomes sui generis. The authority's policy restricts HMOs where more than a stated proportion of properties within 100 metres are already in that use, and the street is above it. The application is refused on concentration, and the landlord is left with an unlawful use, a licensing position that no longer matches the planning position, and a seventh room that has to come out.

Check the concentration policy before buying, not after converting.

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.