Merging two dwellings and the loss of a unit

Merging two flats into one is not automatically a change of use, and that single point confuses more householders than any other part of the process. Section 55(3)(a) of the Town and Country Planning Act 1990 makes subdivision a material change of use by statute. It says nothing about amalgamation. So whether you need planning permission to combine two dwellings into one is a question of fact and degree, judged against the local plan rather than settled by the Act.

In much of England the answer is that you do, because the loss of a residential unit is a planning consideration in an adopted plan.

Whether amalgamation needs permission at all

The ordinary test applies: is there a material change in the use of the land? Two dwellings becoming one is still residential use in Class C3, so on a narrow view nothing has changed.

The courts have accepted that the loss of a residential unit can itself make the change material, where the development plan treats housing loss as a matter of planning concern. In an authority with policies protecting housing stock and a published position on amalgamation, the answer is usually that permission is required. In an authority whose plan is silent, the position is arguable.

Three practical routes out of the uncertainty:

1. Ask the local planning authority in writing, through pre-application advice if they offer it. The reply is not binding but it tells you how the planning service will treat the works.
2. Apply for a certificate of lawfulness for proposed use or development under section 192 of the 1990 Act. This is the only formal way to establish that works are lawful, and it produces a document a buyer's solicitor will accept.
3. Apply for planning permission anyway. Where the plan protects housing stock this is the pragmatic answer, because an unauthorised amalgamation discovered on sale is an expensive problem.

Do not rely on council tax merging the bands as evidence of anything. The valuation office and the planning service work to different rules and neither informs the other.

Why councils resist losing a unit

The policy logic is straightforward. Authorities have housing targets, and a net loss of one dwelling counts against delivery in the same way a new dwelling counts towards it.

Beyond the arithmetic, plans protect the existing stock for a mix reason. A borough with many one bedroom flats and a shortage of family housing may actively support amalgamation, because the resulting four bedroom house is the type it is short of. A district with the opposite profile resists it. The policy you are arguing against is often local, specific and recently adopted, so read the current plan rather than a guide to the system.

Expect the policy test to be framed in one of three ways: a presumption against net loss with limited exceptions, a floor area threshold below which amalgamation is acceptable, or a requirement to demonstrate the existing units are unsuitable. Each needs a different application.

The evidence that makes the case

Officers assessing an amalgamation want a small, specific set of documents, and the application usually fails on the absence of one of them rather than on the policy argument.

Existing floor plans with measured gross internal areas for each unit, clearly annotated, and proposed plans with the same. Measured areas, not areas scaled off an estate agent's floorplan.

A schedule comparing each existing unit against the applicable space standard. Where the local plan has adopted the Nationally Described Space Standard, that means 37 m² for a one bedroom one person flat with a shower, 50 m² for a one bedroom two person flat, 7.5 m² for a single bedroom and 11.5 m² for a double, with a floor to ceiling height of at least 2.3 m over three quarters of the floor area.

Evidence about the existing units as homes: whether each has its own entrance, its own bathroom and kitchen, daylight to habitable rooms, any private outdoor space, and whether either has been let in recent years.

A planning statement setting the proposal against the specific policy, naming the policy number and quoting the test. Amalgamation applications are decided on policy compliance, and a statement that describes the works without engaging the housing policy gives the officer nothing to recommend.

Where the existing units are substandard

This is the strongest case, and it is more common than people assume in houses converted in the 1970s and 1980s.

The last row needs real evidence, meaning agent's particulars, the asking rent and an enquiry record, rather than an assertion that nobody wanted it.

Where the two existing units are both compliant, decent flats in an area short of small homes, be realistic. That application is difficult, and the honest advice is often to improve the flats instead.

Fees, the levy and council tax

Three money points that come up every time.

The planning fee is the change of use fee where permission is needed, plus a householder fee if you are also extending. Fees have been indexed annually since April 2025, so take the figure from the current national schedule.

The Community Infrastructure Levy is charged on net additional floorspace. Combining two units without extending creates no additional floorspace, so there is normally no levy liability. If you extend as part of the works, the residential extension exemption may apply, and a self build exemption exists for other circumstances. Both require the right form submitted before work starts, and missing that deadline is the most common way people end up paying a charge they were entitled to avoid.

Council tax will eventually merge into a single band, but the valuation office acts on its own timetable and sometimes needs prompting.

Conditions, obligations and going back

A permission for amalgamation commonly carries a condition requiring the building to remain as a single dwelling, so that converting back later needs a fresh application. That is not a restriction to argue with. It is the authority protecting the position it has just accepted.

A small number of authorities whose plans provide for it seek a planning obligation on the loss of a unit, either a replacement unit or a contribution. Check whether the plan contains such a policy before you budget, because it is not universal.

Reversion is also a practical construction question. If the separating floor and the second kitchen are removed entirely, going back later is a substantial job, and the fire separation and sound insulation requirements that applied to two flats will have to be reinstated to current standards.

Putting the application together

The submission for a straightforward amalgamation is short: a planning statement engaging the housing policy, existing and proposed plans with measured areas, elevations if anything changes externally, and the space standard schedule.

Where the property is in a conservation area and the works involve external alteration, Article 9 of the Development Management Procedure Order requires a design and access statement. Where the building is listed, listed building consent is needed for the internal works as well, and removing a separating floor in a listed building is a substantial intervention that needs its own justification.

The character of a residential use can also shift without any change in the number of units, which is the question examined in the piece on children's homes and the C2 or C3 distinction. The list of report types shows what else a larger scheme might trigger.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

Enter your postcode on PlanScope to see which documents an amalgamation application at your property would need.