Metal roof over purlins

OK. Here goes. I got an awesome deal on an old house, the thing though is it had to be moved and in order to move the house, the roof had to be removed down to the ceiling joists. I knew that I would not be able to put on my metal roofing until the loan for my land went through(about 3 months), so in the rush to avoid rain ruining my house I did this,

-framed up the roof as I wanted
-put tyvex on top of that
-put 2x4 purlins(pressure treated since it would be exposed for a while to the rain but now which I have found out is not good to attach galvanized roofing to.

so my questions are… What are my options as far as attaching the roof to the purlins? One of the guys I spoke to about a quote on the metal said to put roofing felt between the purlins and the roofing to avoid corrosion. I live in a hot climate(south louisiana). Should I worry too much about condensation behind the metal since we don’t really have much of a cold season? The tyvex has done a good job so far of keeping the rain out so I am thinking it would be fine. Would the roofing felt cut to 3.5" applied over the purlins work to keep the metal from corroding? In your experience, what would you do?

i would install 30# over purlins, if anything for, because of condensation from metal.

I would suggest using strips of a heavy I+W at the attachment points (clips) and 30lb for the rest. Good luck!

wouldnt the common sense thing to do would be to replace the purlings with regular lumber?

?? 2x4 treated boards isnt regular??

Tyvek isn’t ideal on the roof deck to begin with but it is up there so that is a moot point.

A synthetic underlayment or I/W across the PT lumber should give you enough isolation.

If you want, it wouldn’t kill you to double up the layers for that matter.

My vote is 30#. There is no asphalt in synthetic paper meaning any condensation from the bottom of the metal (and there will be substantial condensation) will drip off and have no where to go when it runs down to the 2x’s and gets slowed down.

This is the a reason synthetic specs require button cap and nails/ staples. Felt has uses and stands the test of time if protected from UV.