A little background; Another bedroom will be needed if the family is to grow further. For some reason I had always planned on 3 kids. Child #2 is almost here and its a 2 bedroom house. It dawned on me that the best place to add on to this house would be over the master bedroom and enclosed porch/sun room (looks to have the better foundation of 2 additions) with a stairway going where the 2nd bedroom's closet is. I also need to do some roof work before too long and my planned new roof line would fix up a real ugly area in the roof, not to mention eliminate 2 valleys. The major downsides are; I am not sure the house is worth it (the original part of the house is far from square, plumb and level and there have already been a couple rounds of rot repair) and I am pretty sure the existing walls are 2x4 studs. I'd definitely feel much better about doing it if it had 2x6 studs, but can 2x4s support a second story?