For years I've installed 1/2 hardi over 30lb felt stapled to studs. Last week I spoke to another contractor who uses 1/2 drywall over the studs. Then laminates felt with roofing adhesive to the drywall. Then the hardibacker.
He says that is makes for a stiffer wall behind the tile. Does anyone use this technique? Any comments? What type and size screw would I use to make up the additional 1/2"?