Internal alterations and when planning is not engaged

Taking out a wall between your kitchen and dining room does not need planning permission, and the reason is a single line of statute. Section 55(2)(a) of the Town and Country Planning Act 1990 says that works for the maintenance, improvement or other alteration of a building which affect only the interior, or which do not materially affect the external appearance, are not development at all. No development means no application, no fee and no eight-week wait.

That is the general rule for internal alterations and planning permission. It has four real exceptions, and each one catches householders who assumed the inside of their house was nobody else's business.

The section 55 exclusion and what it actually says

Development is defined in section 55(1) as the carrying out of building, engineering, mining or other operations in, on, over or under land, or the making of a material change in the use of buildings or land. Section 55(2) then lists things that are declared not to be development, and internal works sit at the top of that list.

The wording does two jobs. It excludes works affecting only the interior, and separately it excludes external works that do not materially affect external appearance. So repointing, replacing a boiler, rewiring, fitting a new kitchen, re-plastering, moving a bathroom, laying a new floor and taking out a non-structural partition are all outside planning control.

The test is appearance, not effort. A steel beam and three days of scaffolding inside a terrace is still not development. A 40mm change to a window reveal visible from the street might be.

One statutory exception sits inside the subsection itself. Works for the alteration of a building by providing additional space underneath the ground are expressly treated as development, which is why digging out a basement or lowering a cellar floor to create habitable space is caught even though the work is entirely internal. Many London boroughs then require a basement impact assessment as a validation item.

Where internal work still counts as development

Four situations pull internal works back into the planning system.

1. The external appearance changes materially. A new window opening, an enlarged opening, a flue, an extract terminal, a rooflight in a front slope, or an infilled doorway are all external changes even where the work is driven by an internal rearrangement.
2. The building is listed. Internal works to a listed building need listed building consent whether or not they are development.
3. The result is a material change of use. Creating a separate dwelling, a business use, or a house in multiple occupation in an Article 4 area engages section 55(1) on the use limb rather than the operations limb.
4. Space is created below ground. The basement exception above.

Flues and extract ducts are the most common trip. A loft conversion with an internal staircase and no dormer is usually permitted development or not development at all, but the soil vent pipe that has to come up the rear elevation is an external alteration and needs to be assessed against Class B and Class C limits.

Sequence matters here in the same way it does when you are extending a house that has already been extended. The planning question attaches to the external consequence, not to the room you were trying to improve.

Listed buildings are a separate consent regime

Section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990 makes it an offence to execute works for the demolition, alteration or extension of a listed building in a way that affects its character as a building of special architectural or historic interest, unless consent has been granted. There is no internal exclusion. The protection covers the whole building, inside and out, and it applies to every grade.

That means removing a chimneypiece, taking down a lath and plaster partition, stripping panelling, replacing floorboards, altering a staircase, opening up a blocked fireplace or dropping a suspended ceiling can all require listed building consent. Enforcement for unauthorised works is criminal, not civil, and there is no time limit equivalent to the ordinary planning immunity periods.

The practical route is a schedule of works keyed to a plan, photographs of everything being touched, and a statement of significance explaining what the fabric contributes and why the proposed intervention is acceptable. A Heritage Statement covers that ground, and for anything beyond routine repair it is worth having a conservation-accredited professional read it before submission.

Conservation areas are different. Outside listed buildings, internal works in a conservation area are not controlled, because the designation bites on external appearance and demolition. The one thing that does catch people is the loss of a chimney stack, which is an external change even when the motive is internal space, and is dealt with in chimney removal and the character of a terrace.

Creating a self-contained unit inside a house

Section 55(3)(a) is explicit. The use as two or more separate dwellinghouses of a building previously used as a single dwellinghouse involves a material change in the use of the building and of each part of it. Subdividing a house is development even where nothing external changes at all.

The question is whether what you have created is self-contained. Councils look at a cluster of factors rather than a single test:

An annexe for a relative usually stays ancillary. The same physical layout, let to a stranger on an assured shorthold tenancy, usually does not. Lock the door between the two halves and the picture changes again.

Where a house is converted to a small house in multiple occupation for three to six unrelated occupiers, the C3 to C4 change is permitted development under Schedule 2 Part 3 Class L of the GPDO 2015, unless an Article 4 direction has withdrawn it. Many university towns have exactly that direction in place. Check before exchange, not after.

Building regulations and party wall duties

Planning and building control are separate systems with separate consents, and internal alterations frequently need the second even when the first does not apply.

A structural opening needs building regulations approval under Part A, with a calculation for the beam and its bearings. Removing a chimney breast in one flat while leaving the stack above is a notifiable structural alteration. Loft conversions engage Part B for escape and fire separation, Part K for the staircase, and Part L where thermal elements are altered. New or moved bathrooms engage Part G and Part H, electrical work engages Part P, and airtightness work engages Part F for ventilation.

Then there is the Party Wall etc. Act 1996, which is civil law and independent of both. Cutting into a party wall to bear a beam is section 2 work and needs a party structure notice served at least two months before work starts. Excavating within 3m of a neighbour's foundations to a lower depth needs a section 6 notice one month ahead. Serving late is the single most common cause of a stalled terrace project.

Keeping the evidence that nothing external changed

If the works were not development, there is no permission to point at later, and a buyer's solicitor will ask. Build the file as you go.

Dated photographs of every elevation before and after, the building control completion certificate, the structural engineer's calculations, the electrical installation certificate, the party wall award if there was one, and the invoices. That set answers most conveyancing enquiries without any further application.

Where the position is arguable, a Lawful Development Certificate under section 191 of the Town and Country Planning Act 1990 for completed works, or section 192 for proposed works, gives a formal determination from the council. It is the only way to settle the point, and the fee is a fraction of the cost of unpicking an unauthorised conversion. Where a certificate application needs a written case, PlanScope can draft a Planning Statement setting out the facts and the statutory basis for review before it goes in.

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.