I am renovating a 9 year old New Orleans house that flooded during Hurricane Katrina. In removing some of the original vinyl siding, I found out that a moisture barrier (such as Tyvec) was never placed betweem the siding and the plywood. I figure I have one of 3 choices to make - just replace the siding and forget about it, place Tyvec over as many exposed areas as I can during the current renovation or bite the bullet and rip all the siding off, place the Tyvec, then replace the siding. Any thoughts???

Tyvek is good, but it's neither required nor critical. I suppose some coverage is better than none at all, but depending on how much of the siding still exists...I don't know.

If the house is for yourself and for the long run, bite the bullet. If it's for sale, you still might want to do the whole house. Call-backs are a pain in the rear for everyone involved.

This should help.
tyvek home page