I am building an addition to my home in northeast Georgia, a mixed-humid environment. It can be blazing hot in summer and bitter cold in winter, but winter temps rarely go below 30 degrees and I don’t even have the heat pump running in late spring and early fall. We get about 50-60 inches of rain per year, so I included a 16 inch roof overhang all around.

I had planned on installing 1 inch of Styrofoam on the exterior of 2X4 walls and putting Hardie panel directly against the foam with Tamlyn H-trim at the panel joints, air-tight drywall and no interior vapor barrier inside. But, I could also use 3/4 inch Styrofoam, install 1/4 inch furring strips, and then Hardie panel. Or I can put Homeslicker over 1 inch foam. I guess my questions are,

Does Hardie panel really need a gap behind the panels?
Is 3/4 inch enough of a thermal break for Northeast Georgia?

I can find lots of information about using a rainscreen with Hardie plank, but very little about using one with panels.

Part of my problem is that everybody around here sells 3/4 inch blue board. I’ll have to drive to Atlanta to find the 1 inch.