In most cases planning is not required once there is no alteration of the roof line and the windows are at the back of the house. These types of attics are most common and are classed on paper as a storage area, although most likely they are used as spare bedroom or study etc.

Having a dormer in the attic space allows for more head room where the roof comes down towards eves and these types of attics do need planning as we adjust the existing roof.