Start with the work, not its price or description
The planning question is what you will actually build or change. Building operations and a material change of use can be development. Some alterations affecting only the interior, without materially affecting the building's external appearance, fall outside that definition. Calling something a refurbishment, garden room or temporary structure does not settle its planning status. [1]
Write down the whole proposal: changes to the footprint, roof, windows, access and use. Where a project contains several elements, identify a lawful route for each rather than assuming that an extension allowance also covers every associated alteration. [3]
Work through these checks
- Identify the property. Establish whether it is a house, flat or maisonette and how its residential use was authorised. The usual householder extension rights do not apply to flats or maisonettes. Some homes created through permitted development conversion also have restricted rights. [4]
- Check the planning history and constraints. Read previous decision notices, their conditions and any relevant Article 4 direction. Designated areas can have tighter national limits, even without an Article 4 direction. [4][2]
- Test the actual drawings. A permitted development assessment can depend on original walls, previous additions, heights, boundaries, materials and the position of the extension. Meeting a headline depth limit is only one part of that assessment. [3]
- Identify any required procedure. Some rights require an application for prior approval before work starts. Others do not, although you can apply for a Lawful Development Certificate to establish the proposal's planning lawfulness. [1][5]
A useful feasibility record puts the drawing reference beside each relevant rule, with the measurement or evidence that demonstrates compliance. Treat an unanswered question as something to resolve, not an assumed allowance.
Choose the correct next step
Where the proposal complies with an available permitted development right, follow all its conditions and any required prior-approval procedure. Where the issue is uncertainty about lawfulness, a proposed-development certificate is the formal route to a determination. Where permission is needed and is not already available, make a planning application or redesign the proposal. [1][5]
For work to a single house, the application may be householder planning consent. Applications affecting flats are outside that simplified application type and generally use full planning consent when planning permission is required. [6]
Do not use a neighbour's extension as proof. Their permission, original building, constraints or approved dimensions may differ from yours. The assessment is of the proposal at the particular property. [3][4]
Keep separate approvals separate
A planning answer does not settle building regulations. Party wall procedures and private property rights are also separate questions. Record these alongside the planning route so that “no planning application needed” is not mistaken for “ready to start building”. [7][8][1]