When my house was built, the builder put the Tyvek wrap on the frame of the house, then installed the sheathing and then installed the siding. I am about to have my siding replaced and one of the contractors wants to take down all the siding and sheathing and peel off the Tyvek, then put sheathing back on, then Tyvek wrap it and then install the siding. He claims if I don't do this it will void the warranty on the James Hardy siding. I am aware that I may have some sheathing damage, but I don't see any reason to do all this as I can't believe it would void the Hardy siding warranty. Another contractor wants to put another layer of Tyvek on the outside of the sheathing and leave the old Tyvek underneath the sheathing. I am also not sure this would be a good idea since you could trap moisture on the sheathing that would now be in the middle and then I would have mold and mildew in there if moisture did penetrate. I would take any information that someone might have about how to handle the situation.
I can’t imagine that James Hardie will condone the installation of two exterior house wraps (James Hardie calls it : “Weather Barrier”) sandwiching the existing wall sheathing.
The existing sheathing will have moisture in it and probably large amounts of dryrot.
However, you want to install their product, their way, in order to protect the warranty. That’s why it’s important that you have an on-site inspection performed by James Hardie. Make sure you get his report in writing.
Btw, I would not use “Tyvek” or some random caulk. I would use only James Hardie products installed exactly how they recommended. (This includes NOT caulking above windows. This drives every installer crazy, but is required by James Hardie.)