What is a S257 HMO?

Section 257 HMOs (after s257 of the Housing Act 2004) are buildings which has been converted, or part converted, into self-contained flats that did not comply with the appropriate building standards and still do not comply with those standards, and less than two-thirds of the self-contained flats are owner occupied. This page covers England; Wales has its own equivalent rules and separate licensing thresholds.

Buildings converted into self-contained flats will generally not be S257 HMOs, provided that they were converted in accordance, or now comply, with the appropriate building standards required at the time of the conversion.

A building is an HMO under s257 if all three of these apply:

• The building has been converted into self-contained flats

• The conversion does not meet the appropriate Building Regulations (i.e. not in accordance with 1991 standards or later)

• Less than two-thirds of the flats are owner-occupied (the rest are rented out)

The appropriate building standards, as a minimum, will be the 1991 Building Regulations. If you don’t have a building certificate for the conversion, it’s very likely your building is a s257 HMO. Please seek professional advice if you are unsure.

A flat counts as owner-occupied under s257(4) where it is occupied by a person holding a lease of more than 21 years, by the freeholder of the block, or by a member of that person’s household. Anything else, including a flat let on an assured shorthold tenancy, counts towards the rented proportion.

Often these blocks were converted into flats before 1st June 1992 and did not comply at that time with the Building Regulations 1991.

Section 257 HMOs are not C4 dwellings, but they are subject to licensing where additional or selective licensing is in place. 

Section 257 HMOs and planning

This is the point most often misunderstood. Section 257 is a housing definition, not a planning one, and the two do not line up.

For planning purposes each self-contained flat in the block is a Class C3 dwellinghouse in its own right. The building is not Class C4. The Use Classes Order 1987, as amended in 2010, expressly excludes a converted block of flats to which section 257 applies from the Class C4 definition of a house in multiple occupation.

Two consequences follow, and both matter:

• the Class L permitted development right (C3 to C4 and back) is irrelevant here, because the GPDO definition of dwellinghouse excludes flats
• an Article 4 direction withdrawing Class L therefore does not bite on self-contained flats, so a s257 building is not caught by it

In short, a building can be a s257 HMO for licensing and management purposes under the Housing Act 2004 while remaining a group of C3 flats for planning purposes. Being a s257 HMO does not by itself create a need for planning permission.

What this means in practice

• Even though each flat may be self-contained, the building as a whole is classed as an HMO

• The landlord or freeholder (or managing agent) may have HMO-related responsibilities for the entire building, especially around fire safety, common areas, and maintenance

• Some councils require HMO licensing for s257 buildings if they meet their local scheme criteria (especially additional licensing schemes)

S257 licensing

Unlike most other HMOs, Section 257 HMOs are not automatically subject to mandatory licensing. S257 HMOs are subject to licensing where additional or selective licensing is in place. This will vary depending upon the local authority. So please check locally.

Where a s257 HMO is licensable, the Housing Act 2004 does not apply to it in unmodified form. The Houses in Multiple Occupation (Certain Converted Blocks of Flats) (Modifications to the Housing Act 2004 and Transitional Provisions for section 257 HMOs) (England) Regulations 2007 (SI 2007/1904) adjust Parts 2 and 4 of the Act for these buildings, including who counts as the person having control and what the authority must be satisfied of before granting a licence.

Additional Licensing – Additional Licensing requires houses in multiple occupation shared by 3 or 4 unrelated people who are forming 2 or more households and who share facilities such as kitchens and bathrooms, to have a licence. Although the legislation refers to ‘houses’ this does cover a variety of housing types including flats. A designation under section 56 of the Housing Act 2004 may include s257 HMOs, but it does not have to, so the position varies between authorities and between schemes. Note also that a s257 HMO is defined by how the building was converted and by the pattern of ownership, not by the number of occupiers.

Selective Licensing – Selective Licensing requires most private rented properties within a designated area to be licensed. It means that houses need to be licensed where they have a family or one or two tenants living there. Like Additional Licensing, although the legislation refers to ‘houses’ this does cover a variety of housing types including flats.

Typical conditions of a licence (if required)

• Fire-safety upgrades (FD30S doors, interlinked alarms, emergency lighting)

• Management of common parts (lighting, refuse, structural maintenance)

• Periodic inspection records and gas/electrical safety certificates

Applying for a licence

• Apply through the council’s portal, typically using its HMO licence application form

• Provide layout plans, a fire-risk assessment and current safety certificates

If licence not required

• Still ensure compliance with The Licensing and Management of Houses in Multiple Occupation (Additional Provisions) (England) Regulations 2007 (SI 2007/1903), which are the management regulations that apply to s257 HMOs

• Comply with the Regulatory Reform (Fire Safety) Order 2005 in the communal areas

• Keep a written fire-risk assessment and record of safety checks

S257 HMO Action Plan

If you own or manage a converted building:

• Check whether the conversion met 1991 Building Regs standards

• Confirm how many flats are owner-occupied

• If less than two-thirds and not compliant, it’s a s257 HMO

If so:

• Review your council’s HMO licensing policy, as you may need to apply for a licence

• Ensure fire precautions, common-area maintenance, and management standards comply with The Licensing and Management of Houses in Multiple Occupation (Additional Provisions) (England) Regulations 2007 (SI 2007/1903)

• Keep proper records for safety inspections and repairs

Council tax

Since 1 December 2023 most HMOs are valued as a single dwelling for council tax. Section 257 HMOs fall outside that change because the flats are self-contained, so each flat keeps its own council tax band and the normal hierarchy of liability applies.

Section 254 HMO

Section 254 HMOs (after the section in the Housing Act 2004 that describes them) are buildings where there are the sharing of some basic amenities. These are the types of properties that people most associate with HMOs, such as shared student houses or bedsit accommodation, where the bedsits share kitchens and / or bathrooms, etc. These are generally C4 or Sui Generis HMOs.

Page updated: 22nd July 2026