floor joists help codes

I want to use the attic as a nice modern living space. It’s framed out for a bathroom and a bedroom. The floor joist are 2x4s. I know it’s supposed to be bigger but there’s no way that’s possible. I was wondering if I could sister every 2x4 in the floor to support this attic. Even if I have to...

Hi everyone. I am obviously new here but but not a new DIYer :) Anyway came across this forclosure that has been gutted & an upper addition was added. Well when they did all of this, they did not have a permit. Needless to say things were done wrong Namely the floor joists... In order for us to...