I recently added a FROG (finished room over the garage). At the bottom of the steps leading to this room is a small foyer that leads into the kitchen which is tiled. I wanted to continue the tiling from the kitchen into this foyer, but the new plywood subfloor is slightly too high to allow me to add the durorock. I spoke to a tile installer who suggested using a membrane vice the durorock. He said this would allow the correct height to allow the tiles in the kitchen and foyer to be at the same level. Has anyone herad of this type of membrane? Where can I get it? and how do I install it?