AFAIK 'flat' isn't a common term in American English (I'm a Brit living in America and I've had friends who'd never heard the term). Maybe 'apartment' could be added to the popup translation for any Americans learning?
Tapadh leibh! :)
Nah, we can handle it. We read Brit mysteries and watch Inspector Morse on Public Television. 8~)
Any way, flat makes sense as it is usually all on one level. I kind of like it.