Lately I have been seeing & getting numerous questions on the use of WRB’s or Weather Resistive Barriers. For example; do I need it if I am using foam? If I am installing foam, should it be placed over the foam or under it? According to the ZIP system, I don’t need one, is this really a good way to go? Then of course the ever famous should I use tar paper or Tyvek? Needless to say that sounded like a great article idea so here is my take on it.
So what say you?
Tyvek on the outside of foam would be the primary water resistant barrier & allows for full integration with the windows assuming they are not inset (though there are ways even if they are)
Tyvek under the foam can serve a few purposes besides being the last line of defense against water - many like it because once it is up the structure is dried in & it doesn't matter when the foam is installed - it also makes for a good bond break between the foam & sheathing as some have had issues with different rates of expansion & contraction
Can you get away with using an approved foam & tape & no Tyvek - yes, just like you can with a Zip-Wall system assuming things were installed properly which gets down to what is the skill level of the crew installing it. Of course I happen to recall an interesting "lessons learned" on Joe L's house where he showed pics of where the foam panels had separated - this is one reason why I suggest two thinner layers (instead of 1 thick one) of foam along with a Tyvek style product - it is pretty cheap insurance