In many locations there are pre-defined works to buildings that do not require permission, provided that they adhere to a strict set of rules. While planning approval is not formally required for such works in these areas, it is always recommended to seek formal confirmation of this status from the local authority in the form of a Lawful Development Certificate.
An application for this certificate will generally require a similar set of drawings to a planning application, but the process is slightly different, and your scheme cannot be refused provided it complies with the prescribed rules. As with planning applications, these would generally be applied for towards the end of Phase 1.