My house is 3/4 crawl space foundation 1/4 slab from a garage conversion. The center of the crawl space portion is sinking and we have been having problems with the wooden subfloor rotting in the rooms along it. How do we stop this from happening? We also found a shower problem that we fixed.
Jeannie, the most important thing at this point is to determine the source of all of the moisture that is causing the problem. Once you've done that, I feel fairly confident that the subfloor will eventually dry out and the sinking in the crawl space should halt, too. How long ago was the shower leak repaired? Does your crawl space have ventilation? If it has vents, I would open those to get some air moving around down there. If not, leave the access door open but install some sort of screening or metal grill to keep animals and small children out. After several days of ventilation, take a flashlight in to inspect the subfloor and the area that has been sinking. If the subfloor appears to be drying, then your problem may be solved. Of course it's always possible that there could be two separate water issues, so keep an eye on things down there.
However, if the moisture level down there doesn't appear to have changed, then it's time for a little more detective work. Are there any other water or drain lines in the proximity of where the subfloor is rotting? If so, with the water running inside the home, use a rag to run along the surface of the pipes to determine if there are any additional leaks. For the ground to be sinking and plywood to be rotting, my guess is that it would be fairly significant. Always be careful when working in a crawl space - it can be a good idea to wear gloves as there might be all sorts of bugs and critters in there.
If you find any leaks, they should of course be corrected. If not, the next issue to examine is the site drainage around the house. If it appears that water is collecting near the crawl space walls after a rain, some re-grading may be necessary. I suggest also inspecting your gutters and downspouts to ensure they're working properly. If any of the gutters are overflowing and dumping water next to the crawl space, they could easily be causing your problem. The same is true if the downspouts aren't getting the water away from the house.
Some yards are almost impossible to grade away from the house. If this sounds like your situation, I suggest talking to a landscape contractor about installing a French drain in the problem areas adjacent to the foundation. This should catch the water before it's trapped under the home.