Does anyone live in a 2.5-storey house in NF?

The reason I ask is because I have one in the downtown area (built in 1910) and the attic is finished with regular stairs leading up. It seems that all the houses in the area of this style (American Foursquare, 2.5 storeys) have finished attics. Some seem to have people living up there, some don't! I had guests staying up there with a queen bed and some light pieces of furniture.

What I am really wondering is:

1. Were these attics intentionally built as livable space (it seems that way, but I would like confirmation) - or were they built to be finished by the homeowner (the finishing on mine definitely was done within the past decade or so).
2. Going by nail patterns, the joists for the floor of the attic are 24" on-centre, which is not exactly heavy capacity (and this spacing is never used for floors)... so... is it safe to put some heavier pieces of furniture up there (like a sectional sofa?!)?

Any help or insight would be greatly appreciated! Thank you!!!