We bought an end terrace in a relatively new development a few years ago and it was never going to be a forever home as it has a quite small ground floor. We have a side garden that no one else in the development has and thought about a single storey extension to the side to make a bigger kitchen diner and create a hallway so you don't have to go through the living room to get to the kitchen. However, building costs are mad at the moment and building the extension would probably cost more than the value it would add to the house.
My questions are would it be worth getting planning permission for the extension before we sell? Would that potentially increase the value? Would you be more likely to but a house with planning already in place for an extension?