You might want to check for fire code violation. At least in my state/county, there is a legal occupancy limit with a publicly posted placard stating the limit. If you pack the overflow with chairs, there's a good chance it's being exceeded.
I'm not sure what the criteria is. It might be related to how fast the room can be evacuated in the event of a fire. With a fully packed chapel/overflow/cultural hall, I can see that being a concern.
I do know we had to divide a student singles ward that was meeting in a institute building as the Sunday services were breaking fire code. (Or so I was told.)