The briefest version of the problem is this: We've had damp wallboard in
the bathroom (part of the master bedroom addition) since we bought the house
two years ago. The guy we bought the house from was a builder of some sort
(not a good sort, evidently) and put the addition on himself, the summer we
bought the house. Repair guy 1 said the dampness was from an ice dam, he
replaced the wallboard. It got wet again. Roofer two said that it was
either seepage from the fan vent (which he repaired) or water coming from
the old roof section on the second floor, running under the roof of the
addition. So we put on another roof over the second floor - again, a
reasonable suggestion, because that roof was getting really old. He also
replaced the wallboard. It took a few more months to get damp, but it got
wet again. We called Roofer 2 back, and he suggested we re-flash the
addition, since we've had other problems with leaking around the addition's
flashing. So we did that. The wallboard not only didn't dry out, it
completely fell in. (That was the short version. The long version is the
same, but with a lot of swearing.)

Ok, so it's been raining for about three days. My husband and I pulled down
all of the wallboard in the bathroom, pulled out the insulation, and now
we're looking directly at the underside of the 1.5 year old roof. I'm
seeing wet wood (the flat sheets of roofing wood are wet - the stuff that
looks like particleboard, but isn't), lots of water dripping through nail
holes, and something that looks like a purple plastic 6 inch by 24 inch
thing, nailed to the underside of the roof. Water is dripping out of that,
too.

What the hell am I looking at? What is the plastic thing? Why is it
there? Why is water coming through nail holes, if the wood has new asphalt
shingles and new flashing?

Advice, please? We've already spent a fortune not repairing this problem.
Before I call another roofer, I want to be able to be sure that this is the
LAST time I'll be replacing the damned wallboard.

Thanks.

Donna