Hi, I am looking to raise the height of my floor to match an adjoining floor. I have a 1930's house in which the front half of the second floor was always meant to be a finished area and the back area was not. This means that 2x8s were used on the front half and 2x6s used on the back half. Before we bought the house, the back half was finished with an additional bedroom and bathroom. The floorboards underneath have some bounce in them since they are the only "subfloor" under the carpet and have been abused for years. I've already put new hardwood floors on the front half of the house so now I face a significant height difference between the two floors. The other thing that complicates this is that the joists for the two halves of the house actually run perpendicular to each other.
So I am first trying to figure out how to raise the height of the floor to get a good starting point and then how to best install the hardwood floors. Originally I was thinking that I would sister another, taller joist to the original 2x6s and then just subfloor as usual, but I think it's going to be difficult to tie in at the ends of each joist. I also thought about just ripping a 2x4 down and stacking this on top of the existing joists to get the height I need. Where I am at now is to just lay 2x4s down on their wider side, perpendicular to the current joists and screwing them in. By running them this way, I think it helps with the direction of the hardwood floors and it also helps to brace the existing joists while gaining the height I need. I would then subfloor with 3/4" plywood and maybe another 1/4" or 1/2" to get the height I need. Then add the hardwood floors.
My worries are making sure this isn't too much weight to add and just keeping the joists from shifting. If anyone has any suggestions or thoughts, and has experience in this, I'd love any advice. Thanks!