Weird position of supporting wall

The picture shows a supporting (load bearing wall).
3 studs are visible in the wall with the joists visible in the picture forefront.
I'm in the process of removing the subfloor but in the picture I get to an area where the supporting wall is in between 2 joists. The footer of the wall is on top of the subfloor! I cannot therefore remove this subfloor in this position. What do you recommend doing? I was thinking of leaving it (cutting around it) and putting my new subfloor to the same height. The subfloor would have to be left in place where it spans those 2 joists at least? But that means I end up work a doorway with weird heights of subfloor.
I guess I could put an additional joist in the middle?

 

Common convention is to cut to the wall and then install blocking so you can nail into that and have the edge of the new subfloor supported.

 

Blocking like a 2x12 but placed perpendicular to the joists?
It's not the new subfloor I'm worried about but the fact that the load bearing wall is supported by subfloor spanning 2 joists and I need to cut it out in the doorway.
If I cut the subfloor in the doorway then it leaves 12" of wall not supported by anything.

 

Just cut your old sub floor to the baseboard molding. That house is old, see it has horse's hair plaster. I also assume that what you torn up was a plank floor. Forget about the studs placement that wall is not going anywhere, it hasn't for probably over 80 years.

 

Isn't a load bearing wall supposed to stop right over a joist? Otherwise what's supporting it beneath? There's nothing below the stud on the left.

 

Walls are always built on top of the subfloor and there is a rim joist out there on the ends of your floor joists to support the outer edges of the bottom plate. What exactly do you gain by cutting the subfloor off way back at the baseboard? Seems like you are creating unecessary work and problems for yourself.

 

I have to level the floor and sister joists.
You see where the doorway is on the left? There is a stud there supported by nothing underneath. That is the area of concern dive I need to remove the subfloor between the 2 joists in the picture.
Also there is no rim joist, there might be a footer/sill plate above the 1" sub floor. But it hangs 12" to left of the joist so it's being supported by the plank between the 2 joists, ie the load is spread between the 2

 

Old balloon framed houses sometimes did that. They seemed to just build walls in the interior. I'm not sure if they were intended to be load bearing to begin with but many do end up carrying some load over time.

If you are certain that wall is carrying a load I would install blocking under the wall between the joists underneath the door opening. Currently there is strength there because of the two layers of flooring bridging the gap between joists but if you cut that out you loose that strength. The blocking will provide a load path from the wall to the joists after you cut away the flooring.

Next run a saw along the base of the wall to cut the flooring and sub-flooring flush with the wall. That leaves you with the wall sitting on top of the two old layers of flooring and everything else is removed to allow for installation of new flooring.

 

Should the blocking be a full 2x12 sitting on top of the beam? If not, just a 2x4 or 2x6?
Attached with only nails?

 

I figured blocking would only be attached with nails so not providing much upward force support?

 

You can attach the blocking with joist hanger brackets. And since you're only installing blocking in one bay you can nail/screw through from the ends.

 

Can 3 nails in blocking support a vertical load?
i would assume of there was a load there it would just bend the nails down over time? The same as it has put a bend in the current subfloor.

 

The foundation supports the load. Nails just keep the blocking from moving. The joists sit on a plate on the foundation, and any blocking used beneath a load bearing wall would consist of the same dimensional lumber as the joists and would also sit on the plate which sits on the foundation.

Unless there is something unusual your picture isn't showing...

 

Blocking is just a 2x4 or similar. The joists are 12".
for the blocking to support properly, it would need to sit on the beams?

 

Not sure if what I said was unclear? In a load bearing situation, if your joists are 12", the blocking should be 12" too. If a load bearing wall is not over a foundation wall but is a load bearing interior wall that is located directly over a beam (with floor joists in between) then by today's standards the entire length of the beam should have had blocking (same dimension as the joists) installed between every single joist along the entire length of the beam... directly over the beam, directly under the load bearing wall plate.

Nails are never ever load bearing unless they are joist hanger nails with a combined shear rating.

 

Ok.
the problem I have then is that this load bearing wall is not directly over the beam (it's maybe 20" away from the beam). So I can't install blocking as it has nothing to sit on.
I could use joist hangers to take the weight?
If not then my only option seems to be to install a full 8' joist in between the 2 existing joists?

In the photo the beam is under where the 2 joists overlap at the forefront of the photo.

 

Yes, you could use joist hangers.

 

Ok.
I'm still not sure why a joist hanger with nails is stronger than the same nails directly in the blocking

 

A joist hanger provides a flat, solid shelf on the bottom for the wood to bear against. Compare it to the small surface area of a few nails run into the end of the joist or block and there is a lot more area supporting the joist with a bracket.

A hanger bracket is supported by 6, 8 or 10 nails spread around the perimeter of the bracket. There are more nails than the 3 or 4 used when toe nailing to better spread the load. And, the nails in the hanger bracket are spaced further apart instead of concentrating the load to a single line of toe nails.

Also, a hanger bracket provides tremendous support to both sides of the joist to prevent twisting under load. For something so simple they do a pretty good job, are inexpensive and are easy to install.