Converting a loft should not require planning permission unless the property is listed, within a conservation area or the roofline is to be altered. And rear dormers that do not sit forward of the principle roof plane and are no higher than the existing roofline can often be installed under permitted development rights (PD). Party wall agreements are required from adjoining properties. You can find more on this and planning regulations at the government’s website planningportal.co.uk.
Adding a dormer provided headroom of 2m in this en-suite bathroom. The large window also helps open up the space and offers panoramic views. ?66,677, Plus Rooms (plusrooms.co.uk)
Lofts must follow strict regulation regarding fire doors, escape routes and windows. And having a permanent staircase and head-height of at least two metres is required for the conversion to be classed as a habitable space. So, plan access early on in the design process to ensure it is easy and safe, and take into account any floor and ceiling build-up resulting from insulation requirements and finishes.