Splitting a house into flats: do I need planning permission?

 

If you want to split a house into two or more separate dwellinghouses, planning permission is normally required. This is not simply a question of both units remaining within Use Class C3: section 55(3)(a) of the Town and Country Planning Act 1990 expressly treats the use of a building as two or more separate dwellinghouses, where it was previously a single dwellinghouse, as a material change of use.

Creating an additional dwelling in a garden, garage or outbuilding will also normally require planning permission. In those cases there may be both operational development and a new residential use to consider.

But what if you buy a house which was divided into flats years ago without planning permission? The answer now depends heavily on when the breach occurred.

 

 

 

When you split a house into flats

 

If you have purchased a property that was split into flats without permission, first establish the planning history and the date on which the relevant breach occurred. If possible, make this part of the conveyancing investigation rather than discovering it after completion.

For England, the enforcement time limits changed on 25th April 2024. The former four-year period can still be relevant where qualifying operational development was substantially completed before that date or where a qualifying change of use to a single dwellinghouse occurred before that date. For breaches falling on or after 25th April 2024, the general period is ten years. The precise breach created by a subdivision needs to be identified carefully rather than assuming that every old conversion automatically benefits from a four-year rule.

If the use has become lawful through the passage of the relevant enforcement period, an owner can apply for a certificate of lawfulness for the existing use. The applicant carries the burden of proving the case on the balance of probability.

Useful evidence can include tenancy agreements, council-tax and electoral records, utility bills, dated photographs, building invoices, bank or letting-agent records and statements from people with direct knowledge. For a use-based case, the evidence should show when the use began and how it continued through the relevant period, including any gaps or changes in occupation.

Deliberate concealment is a separate warning point. Planning law contains mechanisms which can prevent an owner benefiting from an enforcement time limit where a breach has been deliberately concealed. In Fidler v Secretary of State for Communities and Local Government and Reigate and Banstead Borough Council [2010] EWHC 143 (Admin), a dwelling had been deliberately hidden behind straw bales and tarpaulin. The Inspector and High Court treated the concealment works as part of the overall building operation when considering substantial completion. The Supreme Court later addressed deliberate deception and concealment in Secretary of State for Communities and Local Government and another v Welwyn Hatfield Borough Council [2011] UKSC 15. The practical lesson is not that development must satisfy a simple ‘plain sight’ test, but that an immunity strategy should never be built around deliberate concealment.

Different breaches can also attract different enforcement analysis. For example an unauthorised HMO use, a subdivision into flats and unauthorised building works should not be treated as though they all share one automatic time limit. If the history is complicated, establish the lawful planning unit and use before relying on an immunity argument.

 

 

 

What will the council consider on an application to split a house?

 

Where planning permission is required, the council is not simply deciding whether two flats can physically fit inside the building. It will assess the proposal against the development plan and any relevant national policy.

Common issues include the size and quality of each home, outlook and daylight, privacy, noise between units, the effect on neighbouring occupiers, the character of the area and whether the subdivision would result in an unacceptable concentration or type of housing under local policy.

Internal floor areas and room layouts can therefore become planning issues as well as Building Regulations matters. Check the authority’s adopted policies and standards before fixing the layout.

 

Parking, cycle storage and refuse

 

One house becoming two or more flats can increase the number of households using the site. Councils commonly look at car parking, cycle storage, bin storage and collection arrangements as part of the application.

The answer is not automatically to pave the whole front garden. Highway safety, local parking standards, sustainable transport policy, drainage and the effect on the street scene all need to be considered together. If a new or altered vehicle access is proposed, see our guide to dropped kerbs and highway consent.

 

Flats are different from an HMO

 

Splitting a house into self-contained flats is not the same planning use as creating a small HMO. Separate flats are individual dwellinghouses, normally within Use Class C3. A small HMO can fall within Use Class C4, while larger or materially different HMO arrangements can be sui generis.

That distinction matters for the application route, local policy, Article 4 directions and enforcement. Do not describe self-contained flats as an HMO simply because several households occupy the same former house.

 

Listed buildings and conservation areas

 

If the property is listed, internal alterations needed to create the flats may require listed building consent where they affect the building’s special architectural or historic interest. New doors, vents, meter boxes, bin stores or external escape arrangements can also affect the heritage assessment.

In a conservation area, the change of use question and the design of any external works should be considered separately. The fact that most of the subdivision is internal does not make every associated external alteration automatically acceptable.

 

Planning permission and Building Regulations are separate

 

A flat conversion can require substantial Building Regulations work for fire separation, means of escape, sound insulation, ventilation, drainage and other matters. Building Regulations approval does not grant planning permission, and planning permission does not prove Building Regulations compliance.

The design should therefore be developed with both regimes in mind. A planning layout which cannot sensibly meet fire or acoustic requirements may need to be redesigned later.

 

What should a planning application show?

 

• the existing lawful use and number of dwellings
• existing and proposed floor plans
• the number and size of the proposed flats
• private or communal outdoor space where relevant
• cycle and refuse storage
• parking and access arrangements where relevant
• any external alterations, vents, doors or meter boxes
• heritage information where the building or area is protected
• the local planning policies which apply to subdivision and housing mix

 

Page Updated: 9th September 2026

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