Topic 11

Flats, conversions and HMOs

Guidance for flat owners, landlords and investors on alterations, house conversions, HMOs and local requirements.

20 articles

Altering your flat

01Do flats have permitted development rights?Flats and maisonettes do not have the householder permitted development rights used for ordinary house extensions and roof enlargements. That does not mean every alteration needs planning permission: check the particular work, its effect on the building and any separate rights or restrictions.02Extending a ground-floor flatExtending a ground-floor flat requires planning permission, even when it has a private garden. The scheme must also resolve rights under the lease, its effect on other homes, building regulations and any relevant party-wall or sewer requirements.03Freeholder and landlord consent for alterationsRead the lease before altering a flat: it may allow the work, require written landlord consent or prohibit it. Planning permission and building regulations approval do not replace the consent or property rights required under the lease.04Replacing windows and doors in a flatA genuinely like-for-like window replacement in a flat will not normally need planning permission, but a change in appearance or size may. Check the lease, heritage controls and building regulations separately; an entrance fire door also needs a fire-safety-specific specification.

Converting a house into flats

05Can I convert my house into flats?Converting a house into separate flats requires planning permission. Whether it is acceptable depends on the council's conversion and family-housing policies, the quality of each proposed home and whether the building can meet the relevant technical requirements.06Borough rules on losing family homes: minimum original size and keeping a family unitThere is no London-wide minimum original house size for conversion and no single rule requiring the same family flat in every borough. Read the adopted policy for the address: it may control the existing size, any enlargement, the retained family accommodation and other suitability criteria.07Space standards and unit mix in conversionsNew flats formed by conversion should be designed against the applicable planning space standards, not just a minimum bedroom area. In London, assess the whole dwelling under London Plan policy D6 and the borough's requirements for the number and size of homes.08Building regulations for flat conversions: fire separation, escape routes and soundConverting a house into flats is a material change of use under the Building Regulations. The design must address the new dwellings and their shared parts together, particularly fire separation, safe escape and sound insulation between homes.09Sound testing in conversionsFlat conversions normally need pre-completion sound-insulation testing of the separating construction. Agree the sampling with building control and an acoustic tester: the purpose is to check performance between the completed homes, not merely the specification of an insulation product.10Splitting gas, electricity and water metersSeparate flats need a planned utility and billing arrangement, not simply extra meters attached to the old supply. Ask the relevant networks, water company and energy suppliers to confirm capacity, connections, meter installation and the work that remains your responsibility.11Setting up the leases for new flatsNew flat leases should be prepared by a property solicitor alongside accurate plans and the building's management arrangements. Each lease must identify what is owned, the rights needed to use it and how the structure, common parts, insurance and shared costs will be managed.12Turning flats back into a single houseCombining flats into one house may need planning permission, depending on whether the change is material and on local housing policies. It also needs a separate building-regulations assessment and legal work to resolve the existing titles, leases and property rights.

HMOs

13HMO use classes: small HMOs (C4) vs large HMOs (sui generis)For planning, Class C4 generally covers a small HMO occupied by three to six unrelated people sharing basic amenities as their main home; larger HMOs fall outside that class as sui generis uses. The separate licensing threshold can start at five occupants, so planning and licensing must be checked independently.14Article 4 directions on HMOs across LondonHMO Article 4 directions remove specified permitted-development rights, usually the change from a C3 home to a small C4 HMO. They are common in London but their boundaries and effective dates differ, so check the actual property against the council's operative direction rather than a general borough list.15Planning for large HMOsA proposal for a large HMO needs its own planning assessment and will normally require a full planning application for a material change of use. The council will consider the local housing policy, accommodation quality and effects on neighbours; an HMO licence does not grant planning permission.16HMO licensing: mandatory, additional and selectiveMandatory licensing covers qualifying larger HMOs across England; additional licensing extends licensing to specified smaller or other HMOs locally; selective licensing covers specified rented homes in designated areas. Check the property against each scheme's legal scope, because planning permission and an Article 4 direction answer different questions.17HMO room sizes, kitchens, bathrooms and fire safetyAn HMO must satisfy the applicable sleeping-room conditions and provide suitable shared facilities and fire precautions. The national minimum bedroom figures are only a starting point: local standards, the layout and permitted occupancy can require more space and different facilities.18Badly converted flats treated as HMOs (Section 257)A building converted into self-contained flats can be a Section 257 HMO where the conversion fails the relevant building-regulations standard and less than two-thirds of the flats are owner-occupied, subject to the statutory scope and exclusions. Self-contained facilities do not by themselves take a converted block outside HMO law.

Rentals

19Minimum EPC ratings for rented homesAs checked on 2 October 2026, covered privately rented homes in England must normally have an EPC rating of at least E, unless a valid exemption is registered. The government plans a higher standard for 1 October 2030, but that is not the minimum currently in force.20Short-term lets in London: the 90-night ruleIn London, residential premises can generally be used for short-term sleeping accommodation for up to 90 nights in a calendar year without that use becoming a material change of use under the specific London rule, provided the council-tax condition is met. Exceeding the allowance requires planning permission; lease, safety and other obligations remain separate.