If you are thinking of having an extension or loft conversion carried out, then in many instances it can be built without the need to apply for formal Planning Permission.
It can be built under Permitted Development.
To meet Permitted Development, then certain criteria have to be fulfilled. The area, volume, height and position of the development together with the materials that you may want to use can all have an effect on whether the proposal is allowed.
Recently the size of certain extensions under Permitted Development has been increased but certain conditions have been attached, for example, you may have to consult your neighbour. Other legislative requirements are still likely to be needed for example; Building Regulations and The Party Wall Act may apply.
The Permitted Development rules can be quite complex and it would be easy to be tripped up. If you would like to discuss whether your project falls under Permitted Development then email Alan: firstname.lastname@example.org