Vapor barrier for crawl space with very uneven floor

We live near the mountains, and one part of our house is literally built over a huge rock. The rock sticks up in the center of the crawl space to within 12" of the floor joists, and the crawl space height goes to about 48" at the outsides of the foundation. It would be very difficult to lay a vapor barrier over the rock, and it would likely tear due to sharp edges of the stone. No vapor barrier was installed when the house was built. Would it be worthwhile to attach a vapor barrier to the undersides of the joists?

 

I would endeavor to try and wrap the stone in some manner. The moisture will eke it's way upward. Putting the vb on the joists is not advisable. Remember how you will have to attach it......drive nails or staples, right?.....holes for moisture to infiltrate.
I would try to make several layered attempts from bottom to top, around the perimeter and across the top, taping the vb with a tape similar to Tyvek tape at the joints.
Our church, built back in the early 1900's was literally built over a rock, I am sure similar to yours. We call it "Peter", with Biblical references. It couldn't be blasted away and certainly couldn't be moved.
Of course we welcome pictures to be posted so we can see what you see. There may be an alternative. http://www.doityourself.com/forum/el...your-post.html

 

Short answer is yes, try to cover this with a vapor barrier.

 

I'm by no means an expert in this area but what if - you sealed the rock with drylok or something similar, put the vapor barrier down everywhere except the rock and then sealed the plastic where it meets or overlaps the rock - would something like that work?

 

Here's a picture of the crawl space:
https://docs.google.com/open?id=0B4t...3Q5S21mNnlPb00

The space is 12' wide by 24' deep. There's a concrete apron that extends in about 3'. The duct work visible on top is about 4' out from the back wall. You can see the footer for the back wall in the lower RH corner.

The rock is covered by a thin layer of soil, so sealing it isn't an option. My best plan is to try to move the soil layer to the sides using hand tools, level it up as much as possible, and then spread the vapor barrier over what's left.

Some of the insulation also needs to be redone, since it's upside down.

 

Exactly as I envisioned it. Yeah, your solution may work. Let us know how it goes.
bingo!!

 

Not me my mind was picturing a halfway clean boulder jutting out of the ground. Paint or any kind of liquid sealant definitely won't work!

 

It's exactly what the one under our church looks like, only smaller. Nothing like being able to say your church was built on a "rock", huh???

 

The insulation is not upside down. It's fine.