This is just a primer for now, I will have some pictures and hopefully more information tomorrow...

I am looking at a 3k sqft house, built in 2002, that over looks a huge pond. Its nothing short of our dream home with tons and tons of potential. It was part of a divorce and has been empty for a year or so, and will be a heck of a deal.

There is some kind of rot to about 40% of the floors in the house. the whole middle section from the front to the back. My unexplored plan is to rip all the floors out, sister new joist in beside the rotted one, and replace the floor. I'm pretty confident that I can handle this part. I have replace seals and floor joists before.

What I'm not sure on is how to fix the cause of the problem. Are there any sure signs that would make this an unfixable problem? The interweb suggests to fully enclose the crawl space with a vapor barrier. If this is all I need to do, that should be fairly straight forward.

I'm going to crawl under it tonight and take a lot of pictures. Ill post them tomorrow.

I'm nervous.   What caused the rot in the first place?  A house built in 2002 shouldn't have 40% of the floors rotted.  

I like fixer uppers but I'd inspect VERY carefully.

I used to do floor leveling and foundation repair. If 40% of the floors are rotted. Run, unless you are willing to invest a lot of $$$ into the repairs. It's not as simple as just tossing in some new joists.

First thing you need to do if your serious is get the basement / crawlspace dry. The best and easiest way to do this is to improve ventilation and make sure the terrain isn't part of the reason water is getting under the house. If it is, you are going to have to potentially move some dirt around and or add drains. If it's not a problem then move on to modifying the foundation. Main thing here is airflow, you want good airflow under the house to keep it dry. Easiest way to do that is add vents into key locations, and not at the ground level obviously. Once that's done and it's dry, you will need a hazmat suite and go in with some serious chemicals to kill the mold that i'm positive is present and very hazardous. Once all the mold is killed, you need to rent or buy one of these and take measurements from the side of the foundation and several points to find out where the jousts are sagging, which they will be if the damage is as bad as you say. Depending on what you find depends on how you proceed with the repair.

What we commonly did in this situation if the damaged floor joists weren't complete garbage was sister in fresh joists next to the damaged ones after leveling them out. We accomplished the leveling by nailing two 2x10's together making a beam we used to lift the joists to where they SHOULD be. Then sistering in the new lumber. Make sure the new joists are sitting on the foundation. Also check the *sigh* can't recall the term, but the boards between the foundation and joists and the outer ones to make sure they are not rotted. If they are when you go to level the floor, lift it higher to take the weight of the house off of those pieces and replace them, then sit it back down and proceed with the joist repair. In some cases you may have to install the joists prior to this if the existing pieces are so rotted they can't take the load, you will know pretty quickly as when you start to lift them, they will start to be crushed by the beam you are using to lift.

As for the jacks you use. PM me and I can tell you how to build some if you can weld. DO NOT USE HYDROLIC JACKS BY THEM SELF. And make sure all your jacks reguardless of type are level and wont kick out. If one does and you are close to it, you are asking for some serious hurt, injury or death.

Read up on how to dry a crawl space before you start making holes.  You do not want ventilation to the outside.  Ventilation to conditioned air inside the rest of the house is ok.  You can read more on this (for free online) at building science corporation.  I fixed up my crawlspace last year following their recommendations and it is in great shape now, even with it being very hot and humid here.

ground damp from said pond?

spring under the house?

no vapor barrier if it's peir and beam?

over a slab or basement or crawlspace?

that's a LOT of rot for a 13 yr old house and Rot usually runs far deeper than first look once you start ripping our flooring...

spent the last week resetting windows improperly installed in a guest cabin leading to rot under the frames and rotting out nearly all
trim...ended being 3x the job I thought it would be..