Do you need planning permission for internal alterations?

The following operations or uses of land shall not be taken for the purposes of this Act to involve development of the land (a) the carrying out for the maintenance, improvement or other alteration of any building of works which (i) affect only the interior of the building, or (ii) do not materially affect the external appearance of the building, and are not works for making good war damage or works begun after 5th December 1968 for the alteration of a building by providing additional space in it underground

Why permitted development does not come into it

Permitted development is planning permission granted by the Order for things that are development. Internal works are not development, so they do not rely on the Order. A planning condition or an Article 4 direction that removes permitted development rights does not affect them, and being on Article 2(3) land, such as a conservation area, makes no difference to purely internal work. Read the wording of any condition on the house, though: one that controls how part of it is used, such as keeping a garage for parking, can still apply (see garage conversions).

The exceptions

Listed buildings. No one may alter a listed building "in any manner which would affect its character as a building of special architectural or historic interest" without listed building consent (section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990). That applies inside as well as out: the Planning Portal says consent is needed for any significant works, internal or external. Works without consent are a criminal offence (section 9). There is no application fee. See listed building consent.

New space underground. Section 55(2)(a) expressly leaves out works begun after 5 December 1968 that provide additional space underground. Digging out a new basement is development: see basements.

Two homes from one. Using a building that was a single house as two or more separate homes is a material change of use (section 55(3)(a)), even if every change is internal.

Building Regulations and party walls

The Planning Portal says Building Regulations normally apply to building a new internal wall, removing one, or forming an opening in one. Structure (Part A) is one of the requirements against which regulation 3 of the Building Regulations 2010 tests whether an alteration is "material", and a material alteration is building work. You may need a structural engineer to design the beam and its supports.

Cutting into a party wall, for example to take the end of a beam, is a right under section 2(2)(f) of the Party Wall etc. Act 1996. You must serve a party structure notice at least two months before the work starts (section 3). See do you need a party wall agreement.

What this means for you

For an unlisted house or flat, plan the layout without a planning application, and put the effort into Building Regulations approval and any party wall notices. If the house is listed, talk to the council's conservation officer before you settle the design. If the work includes anything outside, such as new windows or a new door, run it through the permitted development checker.

Getting certainty

If a buyer or lender later wants written confirmation, a lawful development certificate under section 192 of the Town and Country Planning Act 1990 can confirm that proposed operations would be lawful, which includes works that are not development. From 1 April 2026 the fee for works to a house is £274. For a listed building, the listed building consent is the record to keep.