Most loft conversions can be carried out without planning permission. However, you still need to satisfy building regulations requirements. Building regulations are in place to make sure any work that is done is structurally sound, the new room is fire safe and that insulation is placed between the new room and the other rooms below. The specific regulations that apply will depend on the type of conversion you have. As a starting point, the elements covered by building regulations include the following; fire-resistant doors with smoke alarms fitted, floor joists to support weight, sound insulation, stairs for the likelihood of an escape and finally walls to support any existing or new roofs. You can find further information by visiting the government Planning Portal website, local Building Control or contact Ashleigh Clarke Architects.