The Housing Act 2004 sets out the statutory definition of an HMO for the purposes of housing law and licensing — and it is this definition that governs mandatory HMO licensing, additional licensing, and the HMO management regulations. A separate planning use class system (under the Town and Country Planning (Use Classes) Order 1987) determines when a change from a single dwelling (C3 use) to an HMO requires planning permission — and this definition uses different thresholds. A property can be an HMO for housing law purposes without requiring a planning use class change (e.g., a property converted to house five people from three families is an HMO for licensing purposes but its planning status as a small HMO depends on the number of persons and the local Article 4 direction position).
Scotland and Northern Ireland have their own HMO definitions and licensing frameworks — both with a lower mandatory licensing threshold of three or more persons from two or more households (compared to England's five-person mandatory threshold). Wales follows the same Housing Act 2004 framework as England, with Welsh Government guidance on local authority additional licensing schemes.
The Housing Act 2004 HMO definition — the three statutory tests
The Housing Act 2004 ss.254-259 set out three tests for determining whether a property is an HMO for housing law purposes:
- Standard test (HA 2004 s.254(2)) — the most commonly encountered test: A building or part of a building satisfies the standard test if it meets all of the following conditions: (a) it is occupied by persons who do not form a single household — 'household' is defined for this purpose as: a single person; a couple (married or civil partnership couple; or two people living together as a couple, including same-sex couples); a family group (which includes parents and their children or grandchildren; siblings and their partners; grandparents and their descendants; and any other person who was living as a member of the original family before being separated from it). Critically, a group of unrelated sharers (e.g., four friends sharing a house; five students sharing a house) are each a separate household — even if they moved in together and share the property as friends; (b) the occupants number three or more — a property with two persons from two households (e.g., two flatmates who are not related or partners) is NOT an HMO under the standard test (it may be an HMO under the converted building test if the physical structure applies); (c) the property is occupied as the occupants' only or main residence — not a holiday let or a property used as a place of work only; (d) the occupants share one or more basic amenity or one or more basic amenity is lacking — basic amenities are: a toilet; personal washing facilities (bathroom or shower); kitchen facilities for food preparation. A property where the occupants share even one of these amenities (e.g., they share the kitchen) satisfies the standard test. A property where some basic amenities are lacking (e.g., no kitchen in the property) also satisfies this limb. Mandatory HMO licensing threshold: a property that satisfies the standard HMO definition requires mandatory HMO licensing (under HA 2004 s.55) if it is occupied by five or more persons from two or more households — this is the mandatory licensing threshold. A property with three or four persons from two or more households may still be an HMO (for the purposes of management regulations and safety standards) but is not subject to mandatory licensing unless the local authority has designated an additional licensing scheme covering that property type
- Self-contained flat test (s.254(3)) and converted building test (s.254(4)): Self-contained flat test (s.254(3)): a self-contained flat is an HMO if it is in a converted building (not a purpose-built block of flats where all flats meet the standard) and is occupied by three or more persons from two or more households who share a basic amenity. In practice, this test most commonly applies to a large Victorian or Edwardian house that has been converted into flats but where some of those flats are themselves shared between multiple households (e.g., a flat within a converted house shared by four students). Converted building test (s.254(4)): a converted building is an HMO if it contains at least one unit that is not self-contained — i.e., where the occupant of that unit must leave their unit to access a basic amenity (toilet; bathroom; kitchen) that is shared with other occupants of the building. The converted building test is particularly relevant for: older conversions (pre-1991 building regulations); properties converted from single dwelling to multiple units where some units share bathrooms; bedsit-type conversions where bedrooms are rented individually and the kitchen and bathroom are shared. What is a 'household' for HMO purposes: the definition of 'household' is important — it determines whether the occupants of a property constitute two or more separate households (triggering the HMO definition) or whether they form a single household (not an HMO). Key points: (a) a married or civil partnership couple is one household — not two; (b) two or three unrelated individuals sharing a house are multiple households — even if they are close friends; (c) a family group (e.g., three adult siblings sharing a house) may be one household — the extended family definition under HA 2004 s.258 is broad; (d) au pairs, live-in nannies, or carers who form part of the family unit may be treated as part of the same household. Exempt properties: certain properties are excluded from the HMO definition even if they satisfy the tests — these include: properties managed by registered providers (housing associations); religious communities; NHS trusts; prisons; bail hostels; student halls of residence managed by universities
Planning HMO definition — C4 and Sui Generis use classes, Article 4 directions and devolved positions
The planning system uses a different (and separate) definition of HMO for determining when a change of use requires planning permission:
- Planning use classes — C3, C4 and Sui Generis: The Town and Country Planning (Use Classes) Order 1987 (as amended) divides residential properties into three relevant use classes for HMO purposes: (a) C3 (dwellinghouse): a building used as a dwelling by a single person; by people forming a single household; or by up to six people living together as a single household and receiving care (e.g., a supported living arrangement). A standard family home is C3. A house shared by one or two people is C3. A house shared by three to six people who form a single household (e.g., a large extended family) is C3; (b) C4 (houses in multiple occupation — small HMO): a dwelling occupied by three to six unrelated persons who do not form a single household and who share basic amenities. A house shared by four students or four professionals (all unrelated; from different original households) is C4 use. Converting from C3 to C4 is a change of use — but historically this was treated as permitted development (PD) under the GPDO, meaning it did not require planning permission in most areas. However, where a local authority has made an Article 4 direction removing this PD right, the conversion from C3 to C4 requires a full planning application; (c) Sui Generis (large HMO): a dwelling occupied by seven or more unrelated persons from two or more households. There is no size limit within Sui Generis — any HMO with seven or more persons is Sui Generis regardless of the number of bedrooms. Additionally, in areas where an Article 4 direction has been made, ANY HMO (even one with three to six persons — i.e., C4 use) requires planning permission to change from C3. Key distinction between planning definition and housing law definition: the planning definition uses seven or more persons as the Sui Generis threshold — whereas the mandatory HMO licensing threshold under HA 2004 is five or more persons. This means a property with five or six unrelated persons is: subject to mandatory HMO licensing (HA 2004); but is C4 use class (not Sui Generis) unless in an Article 4 area. A property with seven or more unrelated persons is: subject to mandatory HMO licensing; AND Sui Generis for planning purposes
- Article 4 directions, Scotland, NI and Wales: Article 4 directions: a local planning authority (LPA) can make an Article 4 direction removing the permitted development right to change from C3 (single dwelling) to C4 (small HMO) — meaning that in the Article 4 designated area, planning permission is required to convert a house into a small HMO (3-6 persons). Many LPAs with high concentrations of student lettings or HMOs have made Article 4 directions — examples include: Oxford; Cambridge; Leeds; York; Southampton; Nottingham; Bristol; Bath; Newcastle. Where an Article 4 direction is in force: any conversion from C3 to C4 (even a small three-person HMO) requires full planning permission; enforcement action (planning enforcement notice) can be taken against unauthorised C3-to-C4 conversions; the planning authority's local plan policies on HMO concentration (HMO Article 4 thresholds; Article 4 Cumulative Impact areas) apply. Check with the local planning authority whether an Article 4 direction is in force in the property's location before converting. Scotland: the HMO definition under the Civic Government (Scotland) Act 1982 (for HMO licensing) is: a property occupied by three or more persons from two or more households as their only or main residence who share a basic amenity. Scotland's mandatory licensing threshold (3+ persons) is lower than England's (5+ persons) — meaning a Scottish shared house with three unrelated individuals requires HMO licensing. Apply for HMO licence from the relevant Scottish council before advertising or occupying. Scotland has no equivalent C4/Sui Generis planning use class system — planning permission for change of use may be required under planning policies but is assessed differently from England. NI: the Houses in Multiple Occupation Act (Northern Ireland) 2016 defines an HMO as a property occupied by three or more persons from two or more households sharing a basic amenity — same as Scotland's lower threshold. Apply for HMO licence from the relevant NI council. Wales: follows the HA 2004 England definition (same housing law framework); C4 and Sui Generis planning use classes apply in Wales as in England; Article 4 directions available to Welsh LPAs; Rent Smart Wales landlord licence required for all Welsh landlords (Housing (Wales) Act 2014)
Frequently asked questions
Is a house shared by three friends an HMO?+
Yes — if the three friends are unrelated and do not form a single household. Under the Housing Act 2004 s.254 standard test, a property is an HMO if occupied by three or more persons from two or more households who share a basic amenity. Three unrelated friends sharing a house (each a separate household) is an HMO for housing law purposes. However, this property is not subject to mandatory HMO licensing unless it has five or more persons — the mandatory licensing threshold in England is five or more. A three-person HMO may still be subject to additional licensing if the local authority has designated an additional licensing scheme covering that area and property type.
Does my HMO need planning permission?+
It depends on the number of occupants and whether an Article 4 direction is in force. Under planning use classes: three to six unrelated persons is C4 use (small HMO). Converting from C3 (single dwelling) to C4 is permitted development in most areas — no planning permission required — unless your local authority has made an Article 4 direction removing that PD right. Seven or more persons is Sui Generis — always requires planning permission regardless of Article 4 status. Check with your local planning authority whether an Article 4 direction is in force before converting a single dwelling to an HMO for any number of occupants.
What is the mandatory HMO licensing threshold in England?+
Mandatory HMO licensing under the Housing Act 2004 s.55 applies to any HMO occupied by five or more persons from two or more households. Operating a mandatory licensable HMO without a licence is a criminal offence — unlimited fine; potential rent repayment order; entry on the rogue landlord database. Local authorities can also operate additional licensing schemes covering smaller HMOs (three or more persons) — check whether your local authority has designated an additional licensing area. In Scotland and Northern Ireland, the mandatory threshold is three or more persons from two or more households.
How does the HMO definition in Scotland differ from England?+
Scotland's HMO licensing threshold is lower than England's. Under the Civic Government (Scotland) Act 1982, an HMO in Scotland is any property occupied by three or more persons from two or more separate households sharing a basic amenity. All HMOs at this three-person threshold in Scotland require an HMO licence from the relevant Scottish local council — there is no separate mandatory vs additional licensing distinction. In England, the mandatory licensing threshold is five or more persons; smaller HMOs (three to four persons) require a licence only in areas where the council has made an additional licensing designation. Scotland also requires Scottish Landlord Registration for all private landlords (register.landlord.gov.scot), separate from HMO licensing.
- Mandatory HMO licensing — 5+ person threshold, application and conditions →
- Additional HMO licensing — local authority designation and 3+ person schemes →
- HMO planning permission — C4 use class, Article 4 and change of use →
- Article 4 direction — HMO areas, planning restriction and local authority maps →
- HMO fire safety — means of escape, fire doors and detection requirements →
- HMO minimum room sizes — bedroom space standards 2026 →