How to Convert a House to an HMO — Planning, Article 4, and Fire Safety Works

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Many landlords assume converting a house to an HMO is straightforward — add a few locks, take on extra tenants, and collect higher rents. In practice, the conversion process involves planning law, building regulations, fire safety compliance, and licensing, all of which must be addressed before the first tenant moves in.

Planning Use Classes

A standard family home falls within Use Class C3. A small HMO — between three and six occupants — is Use Class C4. In most areas, moving from C3 to C4 falls under **permitted development rights**, meaning no planning application is required.

However, if your local council has introduced an **Article 4 direction** in the target area, this permitted development right is removed and you must apply for full planning permission to change from C3 to C4. Article 4 directions are common in university towns and inner-city wards. See our dedicated guide on [Article 4 directions](/guides/article-4-direction-hmo-planning-permission) for a full list of affected councils.

Large HMOs — seven or more occupants — fall into a sui generis use class and always require planning permission regardless of Article 4.

Minimum Room Sizes

Since 2018, mandatory licensing conditions require minimum bedroom sizes:

Any room below 4.64 m² cannot be used as sleeping accommodation. Rooms between 4.64 m² and the adult minimums may be used by children only. Local authorities can — and often do — set higher minimums than the national standard, particularly in newer schemes, so always check the specific licence conditions for your area.

Fire Safety Works

Converting a C3 home to a licensed HMO almost always requires significant fire safety works. The specific requirements depend on the number of storeys, occupants, and layout, but typically include:

**Interlinked smoke and heat detection:**

Mains-powered, interlinked alarms are required in every bedroom, living room, kitchen, hallway, and landing. Battery-only alarms do not satisfy HMO requirements in most councils.

**Fire doors:**

Self-closing FD30 fire doors (providing 30 minutes' fire resistance) are required to all habitable rooms and kitchen doors opening onto escape routes. Corridor fire doors must be fitted with intumescent seals and smoke seals.

**Emergency lighting:**

Properties of three or more storeys, or with complex escape routes, typically require maintained emergency lighting in hallways and stairwells.

**Fire escape routes:**

All bedrooms must have a viable means of escape. Basement bedrooms typically require an alternative escape window or external door. Any window forming part of an escape route must open to the required dimensions.

**Fire risk assessment:**

A written fire risk assessment, reviewed annually, is a licence condition in most local authorities.

Other Required Works

Beyond fire safety, common conversion works include:

• Installing additional bathrooms or shower rooms to meet occupancy ratios (typically one bathroom per three to four occupants)
• Upgrading kitchen facilities for multiple users
• Installing individual door locks to bedrooms
• Improving insulation and ventilation to meet current standards

Budgeting for Conversion

A typical three-to-four bed HMO conversion in England costs £8,000–£25,000 depending on the existing state of the property, the number of fire doors required, and whether additional bathrooms are needed. Properties requiring full rewiring and fire alarm installation sit at the higher end.

Use our [HMO calculator](/hmo-calculator) to model whether conversion costs stack up against projected rental income for your target property.