Converting a property into a House in Multiple Occupation (HMO) is one of the highest-yield strategies available to London landlords — but it is also one of the most regulated. Getting the conversion wrong can mean a failed licensing inspection, enforcement action, and costly remedial work. This guide covers the practical side of what a compliant HMO conversion involves.
What counts as an HMO?
A property is an HMO if it is occupied by three or more people forming more than one household, sharing facilities such as a kitchen or bathroom. The most common HMO types converted by London landlords are:
- Three to five-bedroom terraced or semi-detached houses converted to 4–8 lettable rooms
- Larger Victorian or Edwardian houses split into 6–10 rooms
- Flat conversions within larger buildings
Licensing — mandatory and additional
All HMOs with five or more people and three or more storeys require a mandatory HMO licence from the local council. In addition, many London boroughs operate additional licensing schemes that require licences for smaller HMOs — sometimes for properties with as few as three occupants. Boroughs with active additional licensing schemes include Newham, Waltham Forest, Barking & Dagenham, and many others.
We check licensing requirements for every borough before we price an HMO conversion. Proceeding without the correct licence is a criminal offence.
Article 4 Directions and planning permission
Many London boroughs have implemented Article 4 Directions that remove the permitted development right to change a dwelling house (Use Class C3) to a small HMO (Use Class C4). In these areas, you need planning permission before converting, even for a three-bedroom HMO. Newham, Waltham Forest, Brent, and several other boroughs apply this restriction.
We establish planning requirements before any project starts.
Fire safety — the most important part of the conversion
Fire safety is the area where HMO conversions are most commonly non-compliant. The requirements depend on the number of storeys and rooms, but typically include:
- Fire doors: FD30 fire-rated doors to all rooms and kitchen, with self-closing devices and intumescent strips
- Fire detection: Interlinked Grade D, LD2 fire alarm system covering all circulation spaces and each floor
- Emergency lighting: in circulation areas where natural light is insufficient
- Fire compartmentation: between floors and rooms, including sealing penetrations for pipes and cables
- Escape routes: protected means of escape in case of fire, including window escape where required
We design and build fire safety compliance into every HMO from the outset, rather than retrofitting it at the end.
Minimum room sizes
National licensing standards set minimum room sizes:
- Single occupancy bedroom: minimum 6.51m²
- Double occupancy bedroom: minimum 10.22m²
- For children aged 10 and under: minimum 4.64m²
Many local councils require larger minimum sizes than the national standard. Always check local requirements before finalising the room layout.
Kitchen and bathroom provision
Councils specify minimum ratios of kitchens and bathrooms to occupants. A typical requirement is one bathroom per five occupants and one kitchen per five occupants, though this varies. Shared kitchens must meet minimum size requirements and be adequately equipped.
What does an HMO conversion cost?
For a typical 5–7 room HMO conversion in London, costs typically range from £40,000 to £90,000 depending on:
- The number of rooms and storeys
- The level of fire safety work required
- Whether additional bathrooms or kitchen facilities are being added
- The existing condition of the property
- Finish level required by the local council licensing team
RCB has delivered multiple HMO conversions across East and South London. We work with the landlord's licensing consultant where required, and we understand what inspectors look for.
How to get started
The right order of steps is: confirm licensing requirements → check planning position → get the building surveyed → price the conversion → submit planning (if required) → apply for licence in principle → build → final inspection → licence issued.
We help landlords navigate this process. For a free initial conversation about your HMO project, call or WhatsApp us on 07359 872594.