Can hump(s) in joists be dealt with when replacing the original hardwood floor?

Q: I recently moved into a two-storey home built in 1936. Two of the joists under my living room floor deflected upward at some point in the past, resulting in a hump in the living room floor. Using a long level, I’ve determined the hump is about an 3/4″ to 1″ above the normal floor surface at its peak, and then becoming less pronounced both back-to-front and side-to-side. The floor on either end of the hump is level.

Can uneven floor joists be dealt with when replacing the original hardwood floor (i.e. removing hardwood and subfloor and replacing with various thicknesses of subfloor to accommodate the hump)?

A: That would be the time to do it. Given that there is as much as 1″ rise in a couple of the joists, it is far too much to simply plane down the sub floor. You would either have to shave down the high joists or shim the others. Of course, this will likely impact your baseboards and other trim too, but that type of hump could certainly be seen as warranting the attention.

Similar Q: I want to install hardwood on a floor that is out of level. I plan to level the floor by installing ripped 2×4 sleepers and then adding 1/2″ or 3/4″ plywood on top. The current sub floor is 3/4″ plywood. The sleepers will go on top of the existing sub floor. My questions are: A) What is the widest advisable spacing to use for the sleepers? B) Can I use 1/2″ plywood instead of 3/4″? C) I assume I will have to place the 2×4’s with the 2″ side down unless a lumber yard has a saw that will rip across the 4″ dimension..? Thanks for any thoughts.

A: I think I would follow the original joists which should be 16″ or 12″ centers. You are going to have to use thicker than half inch plywood though because it will sit above the existing plywood with a space between. 5/8″ Is generally minimum code. For a few extra dollars 3/4″ is definitely the way to go. It is a huge difference over 5/8″.

Related Q: I have flooring in an old house in need of support. It’s wide plank. There is no subfloor and the joists are varied in width. Is there a way to build a sub floor without ripping up the floors, which are in remarkably good shape?

A: Sure, if you can gain access to the underside of the floor. Is there a crawl space or basement? If so you can sister new joists to old.