New roof lights or skylights will not normally require an application for planning permission providing:
If additional volume is created it may be treated as an extension and separate rules will apply (see ‘Loft conversion’).
If you live in a flat, listed building or designated area (conservation area, national park, Area of Outstanding Natural Beauty, etc…) you should check with your Local Planning Authority before carrying out any work.
Learn more on the Planning Portal.
Flats and Maisonettes
The planning regime for flats and maisonettes differs in many important ways to that which covers houses.
Bear in mind that the permitted development rights which apply to many common projects for houses do not apply to flats.