Oops. There goes my US-centrism again. Sorry. Still, it's likely that it will still work, unless you have stone separating those floors. But cutting through plaster and lath is a huge pain, if that's what his walls are.

Around here (North Carolina), 16" on-center is, by far, the most common, but I think code allows up to 24" on-center in certain low-load situations, but I've never actually seen that. I've seen some old homes with them 20" on-center, though.