1. I have looked everywhere and cannot find info on whether I should be taping roof/wall joints on the inside or outside. House is being built in Waco, Tx. Seems to me the inside would be suffice. 2. Is there a preferred underlayment for southern installers? I am installing a metal roof and Hardie siding 3. Any thoughts on roofing materials over flat roof sections. I had TPO planned this whole time but keep second guessing myself.

Flat roof like a industrial building? Or a flat metal roof where the metal go's all the way to the edge? Or are you talking about a flat roof on the first story that butts up against a wall of the second story?

So you are a flat roofer....you sure it is flat? You might want to send a rocket up to be sure.

(1) Assemblies in a hot-humid climate should be designed to dry to the inside (the dry side). That being said there should be no such thing as a flat roof, materials should overlap on a slope in a way to shed water (larger overlaps required for lower slopes). (2) High temp peel n stick installed with overlap per mfg instruction for overlap and slope, etc. I personally would want a gap behind the hardi (would need to check mfg recommendations). (3) No flat roofs.