I'm starting to finish a basement that is 15' high. Where the bathroom is at will only be framed 8' with a sheetrock ceiling and a plywood floor above that for storage. My question is will the walls of this bathroom be considered load bearing? And can I get away with 2x6 joists spaced 16" above? Span is about 13' with another wall between or should I use 2x8's?

Thanks for any input

It depends what you store above the bathroom. If you think it will be crammed with heavy boxes o' junk, go with the 2x8's at 13'.

Depending the width, you can put a 2x6 doubled upset beam to cut the total in half then you can use 2x6's @ 6.5' each.

Example: if your bath is 8' wide, install an 8'7" (rest beam on wall plates) half way down the 13' span. So instead of using 13' long joist, your using 6'6" lengths joist hangered into the beam.