Floor Levels in En-Suite with Wetroom former

24 Mar 2020
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United Kingdom

I am planning an en-suite with a wetroom former tray to be used for the shower area. The existing floor comprises of large chipboard boards which are 18mm thick. The former that the designer has specified is 22mm thick and they have advised me that the floor in the rest of the room will be made up to the same level as the wetroom former by placing 4mm tile backer boards on the existing floorboards. I have specified underfloor heating for the rest of the room (obviously not for the wetroom former area), and the designer says the installer will lay the underfloor heating mats on top of the backer boards. This does not sound correct to me - surely the top level of the underfloor heating mat should be level with the top of the wetroom former so there is no lip when the tiling is done?? Does anyone have any advice? Thanks.
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Need a thicker former, or build it up
Thank you for the reply. The issue with that would be that the floor height would then be above the bedroom, which is to be wood floor.

The more I have read in various places about tiling online and in some books suggests that the chipboard should be removed completely as it is not the best under tiles. A lot of sources suggest WBP (Marine Grade) plywood, covered in backer boards. Therefore, If 12mm structural plywood was used, covered in 6mm backer boards, this would give an 18mm thickness which, when fitted with the 4mm Underfloor heating mats, would bring the level up to 22mm to match the former for tiling. WOuld this be a suitable alternative?
Just thinking about my own project, and whilst I have not used a wetroom former, just sloping the tiles, I have included wet UFH in mine. Whats the reason why you didnt in yours, is it because its not possible with your installation?
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Yes, I would get rid of the chipboard and replace with ply. Do your ply infills In between the joists underneath where the former will go. You will need minimum of 18mm ply fixed to the joists over the remaining floor area (extra noggins between joists if required). You will then have a difference of only 4mm between ply subfloor and height of former. Therefore I would pack up the former by another say 6mm or so to allow for 6mm boards glued and screwed, electric UFH mat followed by self leveller over the lot to bring it up flush to former. There’s always going to be a bit of a lip from the carpet to tiles if you’re going for underfloor heating etc as well, nothing you can do about it, just put a z bar threshold in

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