C3 to C4: the HMO threshold and Article 4 directions

Changing a family house into a small house in multiple occupation for three to six people is permitted development across most of England, which is why C3 to C4 HMO permitted development is the first thing an investor checks. The right comes from Schedule 2 Part 3 of the General Permitted Development Order 2015, and it works in both directions, so a small HMO can revert to a single dwelling without permission too.

Across many university towns and inner urban areas, though, that right has been withdrawn by an Article 4 direction. The direction is the difference between a conveyancing enquiry and a planning application with a parking survey attached, so find it before you exchange.

What Class C4 covers

Class C4 is the use of a dwellinghouse by three to six residents as a house in multiple occupation within the meaning of section 254 of the Housing Act 2004, where the occupants are not a single household.

Three elements decide whether a property is in C4.

The number of residents: three to six. At seven or more the use falls outside C4 and becomes sui generis, which needs planning permission in every case, Article 4 direction or not.

Whether the occupants form a single household. A family, however large, remains C3. Unrelated sharers on separate agreements do not.

Whether the property meets the statutory definition of a house in multiple occupation, which turns on sharing basic amenities such as a kitchen or bathroom.

A house let to five unrelated professionals sharing a kitchen is C4. The same house let to a couple with three children is C3. A house let to eight students is sui generis. The boundaries between the C classes cause similar trouble elsewhere, and our note on children's homes and the C2 or C3 question deals with a related line.

The permitted change between C3 and C4

The Order permits a change of use from a dwellinghouse in C3 to a small HMO in C4, and from C4 back to C3. No application, no fee, no prior approval procedure.

Three qualifications apply even where the right is intact.

It covers the use only. Any building work, such as a rear extension, a dormer, additional bathrooms with external soil pipes, or a bin store in the front garden, is assessed on its own terms and may need permission.

It does not override a condition. Where the original permission for the house restricted occupation, for instance on a new estate with a condition tying units to C3 use, the condition prevails over the permitted development right.

And it does not override a planning obligation or a restrictive covenant. Covenants are private law rather than planning, and a council will not enforce one, but your lender and your title insurer care about them.

How an Article 4 direction removes it

An Article 4 direction is made by the local planning authority to withdraw a specified permitted development right in a defined area. For HMOs the standard form of direction removes the C3 to C4 change, so a conversion that would be permitted development anywhere else requires a planning application.

Two features of directions matter commercially.

They are area based, and the area varies enormously. Some cover a single ward, some cover most of the urban area of a city, and some are drawn around specific streets. A property 200 metres outside the boundary keeps the right.

They take effect on a stated date, and an authority that brings a direction into force less than 12 months after giving notice exposes itself to compensation liability under section 108 of the Town and Country Planning Act 1990. In practice that means most directions are announced roughly a year before they bite, which gives a window for conversions to be completed and evidenced.

A direction does not make HMOs unlawful. It makes them something you apply for, assessed against the local plan policy on housing mix, concentration and amenity. Many authorities apply a threshold policy limiting the proportion of HMOs within a given radius, commonly expressed as a percentage of properties within 100 metres or within a street.

Finding the direction and reading its scope

Start with the authority's own planning policy pages, where directions are usually listed with a map and the confirming resolution. The national planning data service also publishes Article 4 direction datasets, which is a quicker way to check a large area, though the local document remains the authoritative version.

Then read the direction itself rather than a summary of it, for five things:

• the classes of development withdrawn, since a direction may remove more than the HMO right
• the date it came into force
• the boundary, checked against the property's own position rather than its postcode
• whether it applies to the whole of the area shown or only to specified property types
• any exclusions, for instance properties already in HMO use at the date it took effect

That last point is where existing use evidence becomes valuable. A property already lawfully in C4 use when the direction took effect keeps that lawful use. Proving it is the problem, and the evidence is tenancy agreements, council tax or licensing records, and dated correspondence.

Licensing is a separate regime

Planning and HMO licensing answer different questions, and satisfying one does nothing for the other.

Mandatory licensing applies to properties occupied by five or more people forming two or more households. Many councils operate additional licensing covering smaller HMOs, and selective licensing covering all private rented property in defined areas. A property can be lawfully in C4 planning use and unlicensed, which is an offence. It can also be licensed and in breach of planning control, since the housing team issuing a licence is not confirming the planning position.

Ask both teams. A licence is not a planning consent and a planning permission is not a licence.

The amenity, bin and parking evidence

Where an application is needed, the case is made on amenity and the local concentration policy, and the evidence list is short but specific.

Room sizes and the mix of shared space, measured and labelled on the plans, against the authority's own HMO standards where it publishes them. Bathroom and kitchen provision per occupant. Bin and recycling storage, shown within the curtilage and sized for the number of occupants and the collection frequency. Cycle parking. Sound insulation between rooms, where the policy asks for it.

Parking is usually the contested point, and the answer is evidence rather than assertion. A Parking Survey carried out to the recognised overnight and weekend methodology establishes the actual on-street stress in the surrounding streets, which is the figure that answers an objection about parking pressure. Carry it out in a neutral month, avoiding school holidays, and survey the streets the policy identifies rather than the ones that suit you.

Then pull the policy case together in a Planning Statement dealing with the concentration policy, the housing mix argument, amenity standards and the parking evidence in that order.

Where a certificate gives certainty

Two certificates are worth knowing about, and both are applications to the planning authority.

A certificate of lawfulness of existing use under section 191 of the 1990 Act establishes that a current use is lawful. This is the route where a property was in HMO use before an Article 4 direction took effect, or where the use has continued long enough to become immune from enforcement.

A certificate of lawfulness of proposed use under section 192 establishes that a proposed use would be lawful. This is the route where the right survives and you want a formal document for a lender or a buyer, since permitted development produces nothing else to show them.

Both require evidence rather than argument. Tenancy agreements with dates, licensing records, utility accounts, council tax records and witness statements all help. Both carry a fee and a determination period, and both produce a document that materially affects value on resale.

Check the Article 4 position and the licensing regime before you offer on a property, because together they decide whether the conversion is a decorating job or a planning project. Enter your postcode on PlanScope to see which reports an HMO application is likely to need, or browse the full report list.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A lawful development certificate is the only formal way to confirm that works or a use are lawful. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.