Background: I have a kitchen supported with 2x8s 16" o/c over a 13' 3" span. I want to install a 12x24 tile floor, so that much deflection is just not going to work.
Question: I have 2 options I am considering. The first is to sister the 2x8s with another 2x8 so that both would be supported at both ends. The second is to sister the 2x8s with 2x12s but the 2x12 would not be supported on either end as they can't fit between the beam and the floor.
Which one will add more rigidity to the floor?
Side question: Which is more rigid one 2x12 or two 2x8s sistered?