Janitorial Room v. Janitor's Room/Closet?

In the US, which is more common? Janitorial room or Janitor's room/closet?

I think that 'janitorial room' is unnecessarily verbose, but maybe it's just common American usage and not just this author?

The janitor's closet is the more common collocation but either is fine.

Test 1: Corpus of Contemporary American English I ran a collocation search for "janitor's" and "janitorial." In initial results, "room" didn't appear, so it was excluded.

Results:

• "Janitorial closet" - 4 results

• "Janitor's closet" - 34 results

Test 2: Google NGram I ran a frequency search in the American English corpus from 1950 to 2008.

Results:

Regarding my own experience, I'm more used to seeing the space referred to as a closet due to its size and function. (It often doubles as storage space for janitorial supplies.) I've also heard it referred to as a custodian's closet. However, room also makes sense in that context.

I have made and installed building signage for years. On most architectural plans it is referred to as 'Janitor's Closet'. The only distinguishing feature from any other 'Storage Closet' is the inclusion of a sink. However, in practice for door signage, the possessive is not used. It is usually labeled as 'Janitor' or 'Custodian' (depending on the building type). A similar example is on a plan it would say 'Manager's Office' but the sign would say 'Building Manager', 'Superintendent' etc.

When I see Janitorial it is usually used in conjunction with a service or items, not space. Ex. Janitorial supplies, janitorial staff. Only your janitorial staff has access to the Janitor's room where the janitorial supplies are stored. To find the room, look for the room labeled Janitor