Glossary
C3 and C4 use classes for London houses and shared homes
C3 = single dwelling. C4 = small HMO (3–6 unrelated tenants). Conversion between them often restricted by Article 4.
C3 = single dwelling. C4 = small HMO (3–6 unrelated tenants). Conversion between them often restricted by Article 4.
C3 is the use class for a dwellinghouse occupied by a single household. C4 is a small house in multiple occupation shared by three to six unrelated people. The change from C3 to C4 is permitted development nationally, but many London boroughs have removed that right by Article 4 direction, making a planning application necessary.
At three to six unrelated people sharing basic amenities. The change from C3 to C4 is permitted development under Class L — unless an Article 4 direction removes it, which Waltham Forest has done across 807 recorded areas and Southwark across 480.
| Use class | What it covers | Route to it |
|---|---|---|
| C3 | a dwellinghouse, single household | — |
| C4 | 3 to 6 unrelated people sharing amenities | permitted development, Class L |
| Sui generis HMO | 7 or more sharing | full planning permission |
| C3 to C4 where an Article 4 applies | — | householder or full application |
| Waltham Forest Article 4 areas | 807 | most in London |
| Southwark Article 4 areas | 480 | second most |
Sources: the Town and Country Planning (Use Classes) Order 1987 as amended; the General Permitted Development (England) Order 2015, Schedule 2, Part 3, Class L, and Article 4; the Article 4 register from the MHCLG Planning Data Platform, retrieved 1 September 2026, excluding revoked entries. Read at 1 September 2026. Licensing is a separate regime again: a C4 use can be lawful in planning terms and still require an HMO licence from the council.
C3 covers a single person, a family, or up to six people living together as a single household — including care arrangements. C4 begins where three to six unrelated occupiers share basic amenities as separate households. Above six occupiers the use falls outside both classes and becomes sui generis, which always requires planning permission.
Where a borough has made an Article 4 direction covering C3 to C4, converting a family house into a small HMO becomes a material change of use requiring a full planning application. Many inner and outer London boroughs have made these directions borough-wide precisely to protect family housing stock.
The application is assessed on amenity standards, room sizes, waste and cycle storage, and often on the proportion of HMOs already in the immediate area — several boroughs apply a concentration threshold within a set radius.
An HMO application needs a room-by-room schedule with floor areas measured against the borough's minimum standards, a communal space calculation, amenity and sanitary provision per occupier, refuse and cycle storage, and a fire strategy that will also be tested under Part B and the licensing regime.
A worked Barking and Dagenham example of c3 and c4 use classes: with 9 conservation areas — the Becontree Estate (historic) Conservation Area and the Eastbury Conservation Area among the best known — London Borough of Barking and Dagenham (Barking and Dagenham Council) sees c3 and c4 use classes constantly, and there is no borough-wide Article 4 direction, so permitted development generally survives outside conservation areas. Where c3 and c4 use classes pushes a Barking and Dagenham scheme out of permitted development, the route becomes a £548 application decided in 8 weeks rather than a £249 prior approval in 6 weeks.
| C3 | Dwellinghouse, single household, up to 6 people |
|---|---|
| C4 | Small HMO, 3–6 unrelated occupiers |
| Above 6 occupiers | Sui generis — planning permission always required |
| Default C3→C4 | Permitted development, GPDO Part 3 Class L |
| Common London position | Right removed by Article 4 direction |
| Application fee | £610 for change of use |
In much of London yes, because Article 4 has removed the permitted C3 to C4 change.
No. HMO licensing is a separate housing regime and both may be required.
That is sui generis use and always needs planning permission.
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