Yes, both Brian and Andrew are correct. The Mairie will give you the low down on what you can and can’t do. It’s always better to talk your plans through there first and let them guide you on the basis of your plans before you put in a formal planning application. An authorisation is required for all new openings in a facade.
Peter, not having a go, nor being pedantic, just trying to give accurate advice as many people don't know "what's obvious" and that's why they ask questions. Yes, it's bleeding obvious to me too but not to all and there are many stories, too many, where people didn't ask questions when they should have and things didn't work out the way they thought they would ;-)
Excuse us, but you are telling them what they want rather than knowing what they want and we are simply advising. So no need for name calling!
Sorry pedants. Thanks for stating what (for me) is the bleeding obvious. It depends on the area, the barn, the windows and doors and the relevant permissions. In short, don't part with your money until you are sure what you can and cannot "convert". Otherwise you may end up with a barn with furniture in it.
Nice one Peter but not quite right, friends are renovating on the Larzac in the aveyron and can't put in any new openings (thankfully there are existing ones!) which limits the light and style of the coversion enormously. As I said below, it depends on the area.
Brian's already answered - you need to speak to the person responsable for permis de construire in the mairie local to the barn. The situation changes depending on the location of the barn: in some areas no new openings are allowed and the choice of materials used is very limited and controled, in others you can do what you like...!
Interesting one Peter. There is a conversion a couple of villages from us where they kept the big doors but put a door in one of them and have added veluxes only but no windows other than the original openings that have double glazed but very narrow/slit windows added in walls. We went to a party there and it was surpringly light nonetheless because about half had been kept open as a high room and only the dining/kitchen area required daytime lighting. Otherwie the inside is entirely insulated, restructured into a landing with several bedrooms and a sizeable bathroom. It begs the question whether doors and windows are the criteria that make it a conversion?
?? If you can't add windows and doors it wouldn't be a conversion. It would be a barn. With furniture in?
Go to the mairie and ask what would be allowed. Many are happy to see old properties rescued so might well tell you it should be OK. It also depends on how close you are to other properties as well; for instance, windows are not normally allowed less than eight metres from another domestic property.