HMOs & Conversions
An HMO (house in multiple occupation) is a property rented by several unrelated tenants who share facilities. AVA Home Design designs HMO conversions and layouts across London and the Home Counties to maximise lettable rooms and rental yield while meeting room-size, amenity and planning rules, and advises on Use Class C4 versus Sui Generis and Article 4 directions.
HMOs are one of the most profitable things a landlord can do with a property, and one of the easiest to get wrong. The difference between a scheme that lets well and one a council refuses usually comes down to room sizes, amenity provision, and getting the planning class right before any drawings are done.
We design HMO layouts that hit the minimum standards your council licenses against, plan extensions or loft conversions where they add lettable rooms, and confirm the planning route (permitted development, a full application, or Sui Generis) at the very start.
Two regimes run in parallel and people routinely conflate them. Planning decides whether you may use the building as an HMO at all, and turns on use class and any Article 4 direction. Licensing decides whether the property may be let, and turns on occupant numbers, room sizes and amenity provision. A scheme can have planning permission and still be unlicensable because a bedroom is 40mm too small, which is why we design against the licensing standards from the first sketch rather than checking them at the end.
Planning classes and licensing thresholds
- Small HMO (Use Class C4)
- Shared by three to six unrelated occupants. May be permitted development from a family house unless an Article 4 direction applies.
- Large HMO (Sui Generis)
- Seven or more occupants. Always needs full planning permission, and usually more amenity and fire provision.
- Flat conversion
- Splitting one house into several self-contained flats, addressing minimum space standards, parking and amenity space.
- HMO plus extension or loft
- Adding floor area at the same time as the conversion to increase the number of lettable rooms.
- Mandatory licensing
- Since 1 October 2018, an HMO housing five or more people in two or more separate households will in many cases require a licence, regardless of how many storeys the building has. Licensing is separate from planning and runs on the council's own standards.
Who this is for
- Landlords and investors maximising rental yield
- Buyers converting a family house to a rental
- Portfolio owners adding rooms to existing HMOs
Frequently asked questions
- What's the difference between a C4 and a Sui Generis HMO?
- Use Class C4 covers a small HMO shared by three to six unrelated occupants. A large HMO of seven or more occupants is Sui Generis and always needs planning permission. The class affects whether you can convert under permitted development and what the council requires, so we confirm which applies before any design work.
- What is an Article 4 direction and does it affect my HMO?
- Many councils have made Article 4 directions that remove the permitted-development right to convert a family house into a small HMO, meaning a full planning application is needed even for a small C4. Whether your address is covered changes the route entirely, so we check it at the outset.
- How do you maximise the number of rooms?
- We design layouts that meet minimum room sizes and amenity standards while using the floor area efficiently, and where it adds rooms we plan a rear extension or loft conversion at the same time. The aim is the best compliant yield, not the most rooms on paper that a council would refuse.
- Do HMO rooms have to be a minimum size?
- Yes, and the national mandatory licence conditions are specific. Sleeping accommodation must be not less than 6.51 square metres for one person over 10 years old, not less than 10.22 square metres for two people over 10, and not less than 4.64 square metres for one person under 10. No room smaller than 4.64 square metres may be used as sleeping accommodation at all. Councils may also apply their own higher standards, so we design against whichever is stricter.
- Does a sloping ceiling count towards the room size?
- Only partly, and this is the detail that quietly kills loft rooms. Any part of a room where the ceiling height is less than 1.5 metres is not taken into account when determining the floor area. A loft bedroom can look comfortably over 6.51 square metres on plan and still fail once the area under the slope is discounted, so we check usable area against the section, not the plan.
- When does my HMO need a licence?
- Mandatory licensing has applied since 1 October 2018 to HMOs housing five or more people in two or more separate households, in many cases regardless of the number of storeys. Many councils also operate additional or selective licensing that catches smaller properties. Licensing is a separate question from planning permission, and satisfying one does not satisfy the other.
- How many rooms can I actually get?
- Fewer than a spreadsheet suggests, and that is the useful answer. Once you apply the 6.51 and 10.22 square metre minimums, discount everything under 1.5 metres of headroom, and provide the kitchen, bathroom and circulation the council requires per occupant, the honest number often lands one or two below the initial hope. We would rather show you that at feasibility than after you have bought on a yield that was never achievable.
- Do HMO conversions need an overheating assessment?
- Sometimes. Approved Document O applies to new residential buildings, so a change of use or conversion that creates new dwellings can bring Part O into play, while converting a house to a shared HMO that remains one dwelling generally does not. It depends on what your scheme creates in planning and building control terms, and we confirm it rather than guess.