Insulation, Radiant and Vapor Barriers - Replace or install 6 mil vapor barrier

I am finished re-wiring the addition in my house (built in 1970) and am about ready to put up drywall. In the process of rewiring, I pulled down a lot of the kraft-faced insulation. Many pieces ripped in spots. Should I replace with all new faced insulation, or can I put up 6 mil plastic over the entire ceiling and re-use the old insulation? I am in the Philly Burbs.

I suspect replacing the damaged bats will be my answer, but just figured I would ask...

Thanks!

http://www.eren.doe.gov/consumerinfo/refbriefs/bd4.html This is a Dept. of Energy brief on Vapor Diffuser Retarders (VDR), another name for vapor barriers and Air Barriers.

You don't have to take down the old insulaion, just cover it with 6 mil plastic. If you read the brief the real concern is the air barrier when it comes to moisture problems with insulation. The 6 mil plastic can be your vapor/air barrier.

Thanks for the reply!

Follow up question -

How should I handle the recessed cans? I have about 14 4" IC-approved cans in the ceiling. I plan on using unfaced insulation near the cans,but what would I do with a poly vapor barrier?

Recess lighting can be a problem even if they are IC rated. The problem that usually occurs with them is the gap around the perimeter between the sheet rock and canister. The best way to deal with this problem is to install the poly over the canisters and then the sheet rock. Cut an "X" in the poly to expose the canister. Then use a low expanding foam around the perimeter of the canister to seal the gap between the canister and the poly. Let dry and cut off the excess poly and foam.

So the poly wont melt if it is next to the can?

Other than that, the foam idea sounds good.

If done correctly the plastic will not be touching the canister, the foam will seal the gap between the plastic and the canister.