Ok, so I installed 4 jack posts to raise the two adjacent joists by about 3''. This is really just the beginning, but because of my distance from the house, the work cannot happen as quickly as I would like. Basically, my thought on all of this is that I simply want to get this place up and running. I really need to get some new renters in there. So I am not planning on replacing the joist at this time, but rather simply reinforcing the surrounding joists. Of course, I would love to fix everything in the ideal manner, but it is really hard for me to justify pumping more money into this place than I already have...especially considering the fact that it's not currently worth what I owe. Maybe if the market recovers in my area, or I can get a bit more equity in the place, then I can justify spending $5-10k getting things where they need to be, but until that time, I need to limp along as effectively as possible.
First, it is important to know that I did not have much room in which to work under the house. This part of the house only has about 12-14'' of ground clearance. Luckily, where the problem exists is right next to a crawl space vent...and I am a thin, youngish fellow....so I was able to do all of the work so far through that hole. Of course, I am covered in bruises from all the time spent with my arms resting on the brick wall. Good ab workout though...a lot of planking, but I digress.
For the jack footing, I dug down about 10'' into the ground using an entrenchment tool - 2'x'1 perimeter. I then threw down about 2'' of sand, packed it, then 4'' of gravel, packed it, then another 1'' of packed sand. I then used some old bricks I had laying around as the base for the jack stands. I know it's not ideal, but there was not enough room for anything bigger. I suppose I could have poured a rebar-reinforced concrete footing, but I was worried that I might do something improper, then not have the ability to correct the issue...like if I needed to re-position or something. another where I placed the jacks.
I then positioned a treated 4x4 timber that I cut to about 3.5' atop two jack posts I was not sure of exact positioning, so was not able to screw the jack top plates in place before moving everything in place. So some fancy duck taping and my to plates stay in place on the jacks while I maneuvered everything into place. Once the timber was in place, I rotated the entire jack by hand to get the top plates snug against the timber/joists. I then screwed the plates into place to prevent movement as I applied real torque.
I jacked everything up 2-3'' without any problems. Didn't hear any creaking or cracking to speak of. I then placed another to jacks under the same time, just for good measure. When I checked inside the house, there were no cracks in the wall and the floor of the shower have moved back to where it was when the tile was laid. Unfortunately, even checking with a level, I raised one side about 2/8ths of an inch too much and the tile in the shower pan cracked along mostly grout lines on one side. Four tiles (these are small 1.5''x1.5'' tiles) broke along the uneven floor. Also, the mud deck fractured.
So now my question, can I take up tile along the fracture and simply use some thin-set to repair the deck and reinstall the tile, the re-grout? If so, that is what I will do. Then after everything is cured, I will turn the shower on full blast while I crawl up under the house and check for leaks. If I have leaks, I guess I will need to invest in a repair, rather I want to or not.
If no leaks, then I will spend a bit more time placing addition jack stands under other parts of the structure as a bit of insurance.