I have on hand a roll of Tyvek, so as I'm insulating the knee walls of my side attic and I have R19 batts installed into existing walls, putting the Tyvek on the cold side to provide an air barrier and prevent wind washing seems appropriate... Or should I put up rigid foam, and if so is 1/4" adequate? I can get the 1/4" fan fold foam, else I have 1/2" available which would raise costs and be more difficult to manuever into the attic space or require more seams..
Another question arose as I tried figuring this out... A lot of the info that has been linked in other discussions, the web pages are no longer available. Even things I've bookmarked when I started last August have changed or moved. Are "best practices" for insulating undergoing a bit of a period of change right now??