I am about to embark on installing my first wet room. I'm pretty handy but it looks like this one is going to stretch me! I don't know if any one has a take on what I'm about to do? My wife is a wheelchair user so the wetroom is the only way to go. I have an opening of a month to do the work after we've bought the flat and then the pressure is on to get the Mrs in whilst avoiding either crockery breakages or divorce!. This is the deal ; It's a small room, roughly 2.3m x 2.3m square. I want to keep the floor low so as to avoid creating a lip into the room. First I'll take up the floorboards as they have cork tiles stuck to them. Total depth maybe 45mm but don't know until I get busy with my wonder bar and a board chisel. I'll take up the floorboards to check for movement, remedy any concerns with joists, treat and add noggins. Then I would add layers in the following order: 18mm WBP ply- 12.5mm tile backer board, pro-wire loose underfloor heating,(2mm) and then riven slate floor tiles at 10mm thick. That gives me total layer thicknesses of 42.4mm. You can see the discrepancy with the shower tray depth of 30mm. I could add a layer of 12.5mm WBP or backer board under the tray to raise it,( supported by additional structural measures- the tray is heavy) but would this be the way to go?.Regarding the shower tray type. I've found a cement composite,( 30mm thick) with pre-set fall which doesn't require tiling but the rub is that there is no information and how to seal the junction between it and the surrounding riven slate although I could use the waterproof joint tape up the side of the tray but this would present the edge to the fall of any moisture through the tile grout. Is that in itself a problem? If I was tiling the entire area including the tray,( lots of angles to cut- not too confident!), then everything would be coming in at the same level and I'd simply seal flat joints with waterproof gasket tape such as that sold by Marmox. Perhaps I'm being a paranoid tiling robot here but horror stories abound regarding DIY nuts with ideas that are quite beyond them. I don't want to join their gang. If I was a wealthy geezer I'd pass the baby to someone else. Unfortunately my wife has dressed me in full battle fatigues and pushed me out into no-mans land! I'd be interested in anyone with more shoulder pips than me show me the right end of the rifle! Many thanks in advance. . 
