Most loft conversions do not need planning permission unless:

• you live in a conservation area or your house is a listed building;
• you want to put in dormer windows facing the road or if the position of a dormer window would invade your neighbour’s privacy;
• any part of the conversion (including a dormer window) will be higher than the existing roof;
• your house has already been extended to the limit of its permitted development (15% of its original size). You may still be able to add a loft conversion even if you have had some extension work done.