I just bought a 1956 ranch house in Portland, OR and am facing an issue. I've gutted the bathroom for a remodel and it's down to the studs. There was a bit of water damage to the subfloor around the shower/tub so I decided to replace the whole thing.
In the process, I discovered the floor joists are approximately 5' on center 4×8 which is certainly not up to modern day code. On top of that is tongue in groove 2×6 decking for the subfloor. The floor is surprisingly sturdy but many people have already suggested that it would be smart to add more joists, especially since I'll be tiling the floor.
The old joists abut against the concrete foundation, kind of like a mortise and tennon joint (not sure what it's actually called). The foundation is in good condition and doesn't have any cracks and looks dry. The joists span what looks to be the entire length of the house with 4×4 pier supports every 6' or so.
My question is what's the best way to add new joists to the space between the old ones? I guess I need to make a sill against the concrete for which I can attach the new joists. I can't see myself running new 2×8 joists across the entire length of the house, so I was thinking I could go a few feet past the length of the bathroom, using pier supports along the way with concrete pier blocks beneath, and then block off their ends between the original joists. Is that a structurally sound way to do this?
It sounds like my whole floor will need more reinforcement at some point but like I said, it all seems really sturdy for the time being. There aren't any significant sags or bounciness that I can find.
Here's a short video of a walk through the bathroom if it helps: https://www.youtube.com/watch?v=Fb59H0MT3bo (sorry for a couple f bombs! my dirty rotten mouth)
Best Answer
What you are calling a floor joist, appears to be much thicker than a 2x floor joist. Maybe like a 4x8 or something. So it's probably a "bearer" resting on the piers, which would explain why they are far apart. Typically you would then rest floor joists across those beams, (or use Simpson hangers if the floor needs to be nearly flush to the beams -- which is your situation).
This is typical ...
This is where you need to be with Simpson joist hangers:
Can you measure the thickness of the wood that you are calling a floor joist (which is really a bearer)? Also, that beam that is notched badly is not good (most likely). This would be the time to address that notch, which is fortunately very close to the wall. Can you measure the depth of the cut on that notch?
An easy way to do that would be to set a pier underneath the bearer so that no notched portion of the bearer is under stress.
Once you have addressed making sure that the bearer is properly supported, you can then hang joists between the two bearers you showed with joist hangers. Then you would put the subfloor and whatever choice of flooring you want on the joists.