Can I convert a single garage into a self-contained flat?

Rarely on its own. A typical single garage gives somewhere around 12 to 21 square metres, and national space standards set a minimum of 37 to 39 square metres for a one bedroom dwelling. Insulating the walls, floor and roof reduces the usable area further. Most workable schemes either use a double garage, combine a single garage with an adjoining utility, store or small extension, or take the ancillary annexe route instead of a fully independent flat.