What is the typical method to add circuits to a finished building that has a flush mounted breaker panel when there is no attic or crawl space to drop new runs? I was thinking of surface mounting a sub panel above the main panel and running everything new from there. Or maybe mounting a junction box above the panel that feeds into it, and running my new runs into the junction box and down into the panel.
In the trade it's called fishing walls.
Stud finders, fish tape, electrical tape, jab saw, and a drill will be your trusty friends.