I am installing laminate flooring in the upstairs of my home. In one of the rooms, the subfloor was both unlevel and wavy. Also in some spots it would depress about 1/8" to 1/4" depending on where you stepped. I tried to screw it down tighter in those spots, but it didn't seem to help. Finally I pulled it up to find out what was going on. Under the floor are pre-fab OSB i-joists. None of are level with each other. I'm trying to figure out a way to get them level so that I can install a new subfloor. I was thinking about trying to sister 2x4s alongside them, but I don't know the best way to attach anything along the sides.