Re: insulating a 2x3 constructed shower enclosure/exterior wall
I know of no ceement board manufacturer that recommends installing it over 16"oc 2x3's. Also the ceement board isn't waterproof. You'll need to add some sort of waterproofing membrane to your shower system. Since you'll have a membrane in the shower area, the insulation there should not be faced. Use only unfaced behind the wet tiled areas.
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