In a tile shower should I add a layer of plastic for vapor barrier between the studs and kerdi board. Colder climate/ southern Wisconsin Thanks in advance Wall is -Steel siding -Ty vek -1 inch poly foam Insulation -2x6 wood stud wall with kraft faced insulation. -Inside will be kerdi board -Tile
Plastic is a moisture barrier, not a vapor barrier. I don't think you want a moisture barrier behind the wall if it is facing an outside wall, especially in a cold climate. You will get condensation on the plastic inside the wall which leads to mold and mildew.
FWIW slightly off Q, I'm just finishing tile now and went with this right over green drywall; https://www.schluter.com/schluter-us/en_US/Shower-System/Shower-&-Tub-Kits/Schluter®-KERDI-SHOWER-KIT-FLG/p/KERDI_SHOWER-KIT-FLG?facets=false Pretty decent and complete kit, you can buy just the membrane for waterproofing if you already have a pan or gauge your own. My F'up ,,,he added corner pieces and thinset to apply them AND the membrane made it tough to keep everything flat/square. But I'm no expert
