If your extension qualifies as permitted development, you can apply to your council for a lawful development certificate for the proposed work. It gives you written confirmation that the particular design shown in the application is lawful for planning purposes. Homeowners often want this before committing to a build or to have a clear record when they later sell.
You can apply for a certificate before the work starts. If you are trying to establish the lawfulness of work that has already taken place, that is a different application with a different evidence question. This guide covers proposed extensions to houses in England.
Start With the Address and Planning History
The same design can be permitted development at one address and need planning permission at another. Find the original dwelling, then check what previous owners added. Look for planning conditions that remove particular rights, an Article 4 direction, or a designation that changes the rules. A recent estate can have restrictions recorded in its original permission, even where the house itself has no extension history. Flats and maisonettes do not use these householder extension rights.
Sketch the footprint against the original house and the boundaries. The drawings need to show how the proposal satisfies the relevant conditions, including the relationship to previous enlargements. A photograph or estate-agent floor plan can help explain the site, but a measured drawing is a much better basis for demonstrating dimensions.
Put Together a Drawing Pack the Council Can Check
Check the council’s application instructions before submitting. A typical pack includes:
- A location plan identifying the property, with the site outlined as requested by the council.
- A site plan showing the proposed footprint, boundaries and relevant existing additions.
- Scaled existing and proposed plans and elevations, with dimensions where the permitted development rules depend on them.
- A short explanation identifying the relevant permitted development class and showing how the proposal meets its tests.
If the rules turn on a feature that is hard to see in plan, add the evidence that makes it legible. For instance, a section can show the difference between eaves height and overall height. Label the revision consistently so the written case and every drawing refer to the same proposal. See Ashbridge’s planning drawings service.
Example: A homeowner wants to replace a lean-to with a deeper rear extension. The lean-to appears on a recent estate-agent plan, but the planning history shows that it was built long after the main house. The designer establishes the original rear wall, shows the existing and proposed outlines separately and measures the proposal from the original wall. The council can then assess the right dimensions against the drawings.
Keep the Certificate With the Approved Drawings
Keep the decision and the drawing revisions together. If you later move an external wall, change the roof form or make another material change, ask whether the revised design is still covered before instructing the builder. Larger rear extensions that use the prior approval route have a separate process to follow. Building regulations approval and any separate consents also need their own checks.
If you have an address, a few photographs and a rough idea of the extension, you can ask Ashbridge to review the planning route and drawing scope.