C3 to C4: small houses in multiple occupation
Two sharers is C3 and three is C4. How the Use Classes Order draws the line, the amenity standards councils apply and what an HMO application has to prove.
Three sharers is the line. A house let to two unrelated people stays in Class C3, and a house let to three, four, five or six unrelated people sharing a kitchen or bathroom falls into Class C4. That single step is what makes the c3 to c4 permitted development question live, because the classes either side of it are treated very differently by councils, licensing teams and mortgage lenders.
Get the classification right before anything else. Landlords lose money arguing about Article 4 directions when the property was never in Class C4 to begin with, or when it quietly slipped past six occupants into sui generis territory.
What the Use Classes Order actually says
Class C3 covers dwellinghouses used as a single household, which the Order splits into three limbs. C3(a) is occupation by a single person or by people living together as a family. C3(b) is up to six residents living together as a single household where care is provided. C3(c) is up to six residents living together as a single household in other circumstances, which is the limb that catches small religious communities and some supported living arrangements.
Class C4 is narrower. It covers use of a dwellinghouse by not more than six residents as a house in multiple occupation, taking the meaning of that phrase from section 254 of the Housing Act 2004. The standard test there asks whether the building is occupied by persons forming more than one household who share a basic amenity such as a toilet, washing facilities or a kitchen.
So the pivot is the household, rather than the number of bedrooms or the form of the tenancy. Six members of one family are C3. Six students on separate agreements are C4. A couple plus a lodger is a single household in most readings and stays C3.
Above six residents the property leaves both classes and becomes sui generis. There is no permitted development route into sui generis, which is why a landlord adding a seventh bedroom to a licensed six bed HMO is making a planning application whether they realise it or not.
Where councils draw the line in practice
Officers look at how the property is occupied rather than at what the tenancy says. The recurring evidence points are separate rent payments, separate council tax liability, locks on bedroom doors, separate fridges, and whether the occupiers arrived together or were recruited individually.
None of those is decisive on its own. Together they build a picture, and where the picture is ambiguous the safer route is a lawful development certificate rather than an argument with an enforcement officer two years later. A certificate under section 192 of the Town and Country Planning Act 1990 for a proposed use settles the classification before you spend money.
Note: a change of use that takes a property from C3 to C4 is development, and a change that does not is not. Fine grained differences in occupancy therefore have very large consequences, which is the opposite of how most landlords expect planning to work.
Amenity standards that apply once the use is established
Licensing sets statutory minimum room sizes for mandatory licensed HMOs. A room used as sleeping accommodation by one person aged over 10 must be at least 6.51 m². For two people over 10 the minimum is 10.22 m², and for one person under 10 it is 4.64 m². Rooms below 4.64 m² cannot be used as sleeping accommodation at all.
Those are licensing floors rather than planning standards, and most councils apply their own and higher figures through an HMO supplementary planning document. Expect requirements covering communal living space in proportion to the number of bedrooms, kitchen worktop and appliance provision per occupier, bin storage capacity for weekly collections, and secure cycle parking.
The nationally described space standard applies to dwellings rather than to HMOs, so do not quote it at an officer assessing a shared house. Quote the council's own document.
Sound insulation between rooms is a Building Regulations matter that turns up in planning reports anyway, because objectors raise noise transfer and officers repeat it. Deal with it in a sentence and move on.
Parking, bins and the objections that actually land
Two objections carry weight on small HMO applications: on street parking pressure and refuse.
Parking is evidential. A street with controlled parking and good bus frequency supports a low or nil provision case. A suburban street with no controls and a 20 minute bus does not, and asserting sustainability without survey data invites refusal. A parking survey carried out to a recognised method, on the right nights and outside holiday periods, is the only thing that moves an officer who has read 30 objection letters about parking.
Refuse is physical. Six occupants generate more waste than a family of four, and a bin store that cannot hold the containers between collections becomes a street level problem. Show the number and size of containers, where they sit, how far they are dragged to the collection point, and who moves them.
Cycle parking is easy to provide and routinely forgotten. Put it in a lockable store at the rear, not a rack in the front garden.
Where the right has been withdrawn
Inside an Article 4 area every new small HMO needs planning permission. The policies that decide those applications usually combine a concentration threshold with amenity criteria, and the threshold is commonly expressed as a percentage of HMOs within a defined radius of the application property.
Read the policy and the evidence base behind it. Then build the application to answer it directly:
- Establish the current concentration from the council's own licensing register and planning history, and state your methodology.
- Show the room sizes against the adopted HMO standard on a floor plan with dimensions.
- Provide parking survey evidence rather than assertions about sustainable location.
- Show bin and cycle storage in plan, with capacity calculated for the occupancy proposed.
- Address the character of the street honestly, including the balance of family housing.
A planning statement that works through the policy criterion by criterion gives the case officer something to copy into the report. The applications that fail are the ones that describe the property and never mention the policy. Our note on the evidence pack for a change of use application sets out the supporting documents that normally accompany it.
Where the concentration threshold is already exceeded, be realistic. Refusal is likely, and an appeal will turn on whether the council's data is accurate and up to date.
Licensing runs on a separate track
Mandatory licensing applies to HMOs occupied by five or more people forming two or more households, regardless of the number of storeys. Additional licensing schemes extend that to smaller HMOs in defined areas, and selective licensing covers all private rented property in others.
The licensing team assesses room sizes, amenities, fire precautions and management standards. The planning team assesses the use and its impact. Neither grants what the other grants.
That separation produces the standard enforcement case in student districts, where a landlord holds a valid licence for a property whose C4 use was never authorised inside an Article 4 area. The licence is not a defence.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and remember that a lawful development certificate is the only formal way to confirm that a use is lawful.
To see which supporting documents a change of use application is likely to need, enter the postcode on PlanScope. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
How many sharers turn a house into a Class C4 HMO?
Three or more residents forming more than one household and sharing a basic amenity such as a kitchen, toilet or washing facilities. Two unrelated sharers remain Class C3. Above six residents the property leaves Class C4 altogether and becomes sui generis, which always needs planning permission.
Is a couple with a lodger a house in multiple occupation?
For planning purposes a couple plus a lodger is usually treated as a single household and remains in Class C3. Licensing definitions can bite differently. Where the arrangement is unusual or the occupancy is likely to grow, a lawful development certificate for a proposed use settles the classification in advance.
What are the minimum bedroom sizes in a licensed HMO?
For mandatory licensed HMOs the statutory minimums are 6.51 square metres for one person aged over 10, 10.22 square metres for two people over 10 and 4.64 square metres for one person under 10. Rooms below 4.64 square metres cannot be used for sleeping. Councils often apply higher planning standards.
Does the nationally described space standard apply to HMOs?
No. It applies to dwellings rather than shared houses, so quoting it in an HMO application misses the point. The relevant figures are the licensing minimum room sizes and whatever the council sets in its own HMO supplementary planning document for bedrooms, communal space and kitchen provision.
What evidence supports an HMO application in an Article 4 area?
Current concentration data taken from the council's licensing register and planning history, dimensioned floor plans measured against the adopted standard, parking survey evidence collected outside holiday periods, and bin and cycle storage shown in plan with capacity calculated for the proposed occupancy.
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.