Not sure if I've correctly titled this query; my grammatical lexicon is severely wanting.
The phrase in question is from a short story, and is as follows:
"More likely a second—floor-apartment existence."
My heuristic understanding is that the phrase "second-floor apartment" (sans existence) would be correctly hyphenated, and that the phrase "empty-apartment existence" would be correctly hyphenated (to disambiguate from an empty apartment-existence). What happens when you have, as in the example in question, two words which independently should be hyphenated, and a third which should be hyphenated with them collectively, but not with any of them individually?
I've applied an em dash followed by a hyphen, to distinguish 'second-floor' and 'second-floor-apartment' as separately hyphenated entities... Is that correct?
If someone could articulate why that approach is/isn't correct, it would be greatly appreciated.
Edit* Just to be clear: I am the author, and the phrase refers to an existence characterised by living in a second-floor apartment.