What is the difference between planning permission and permitted development?
The difference both is, you need a planning permission if you plan to alter the shape of the roof or if your dormer window is front-facing. You submit your plan to the local council and it is open to rejection by your neighbours or the council.
On the other hand, a permitted development means you don’t have to apply for planning permission. This is usually the case for most buildings that aren’t flats or in a designated area. Semi-detached properties are allowed an extra 50 cubic metres and terraced houses are allowed an additional 40 cubic metres.