Wet room construction over joists with wet underfloor heating - TilersForums.com

[Matttiling]

Hi,

First time here and hoping this is an easy question!

I am installing a wet room upstairs and going back to joists but I also want to install low profile wet underfloor heating (I already have it), what will give me the best surface to tile on and support a bath on top?

So I was planning the below stack but do i need a backing board under the foam? or on top but then would it restrict heat transfer? or should the tanking be underneath the foam?


30cm square tile
------------------------ cement adhesive
Homelux Matting
------------------------ cement adhesive
15mm UFH Foam
------------------------ adhesive
18mm WBP Ply
------------------------ screws
Joists

Thanks for any help, matt

 

[Boggs]

What heating system have you got?

These low build up kits are usually for use on concrete floors not suspended timber floors.

Wet underfloor heating on suspended timber floors usually use 100mm insulation with pipes run on spreader plates with the flooring on top.

 

[Matttiling]

Hep20 low build which is 15mm thick with 10mm piping and includes the diffuser plates.

States it can be tiled on but think something on top for load spreading is a good idea. Would put a backer board on but concerned that it would insulate the wrong way.

Could install ufh then board and then tank on top?

Or Could buy the in joist system but going to work out a lot more expensive (£500 more and still got materials for low profile) and still concerned about heat transfer to the tiles if I use any concrete board? Maybe just 22m ply then tanking?

Cheers matt

 

[Boggs]

If you put the backer board such as Hardie Backer over the heating it will definately stop heat transfer to the tiles.

I would also be worried about the build up into the room and also where your floor meets the wetroom tray former. These normally sit on the joists supported inbetween with 18mm ply and are 30mm thick.
Your build up will be 40mm or more.
Also being a wetroom it would be better to run the heating onto the showering area and this won’t be possible with wet floor heating.
The matting such as Ditra or homelux etc won’t be any good on their own as they help with lateral movement not deflection/bounce found in timber floors.

Would you not be better off with an electric system like Warmup, that way you can run the cables over the tray former to help dry it out quicker.
There are/ used to be other systems on the market that are just tile warmers as opposed to room heaters and you could put in a towel rail as the rooms main heating.

 

[Waluigi]

I think HB is one of the boards that actually should be used over the wet UFH. The insulation boards shouldn’t be used as they will stop the heat, HB won’t. Neither will Pro Ply.

I can’t confess to being an expert on Wet UFH though.

 

[Dumbo]

If you put the backer board such as Hardie Backer over the heating it will definately stop heat transfer to the tiles.

I would also be worried about the build up into the room and also where your floor meets the wetroom tray former. These normally sit on the joists supported inbetween with 18mm ply and are 30mm thick.
Your build up will be 40mm or more.
Also being a wetroom it would be better to run the heating onto the showering area and this won’t be possible with wet floor heating.
The matting such as Ditra or homelux etc won’t be any good on their own as they help with lateral movement not deflection/bounce found in timber floors.

Would you not be better off with an electric system like Warmup, that way you can run the cables over the tray former to help dry it out quicker.
There are/ used to be other systems on the market that are just tile warmers as opposed to room heaters and you could put in a towel rail as the rooms main heating.

Hardi is a cement board which will transfer heat .

 

[Boggs]

Hardi is a cement board which will transfer heat .

Yes, sorry my mistake.

It will slow down heat times though.

Also don’t see the point of a wetroom with heating everywhere but the wet area.

 

[Dumbo]

A warm floor is a warm floor no matter where it is

 

[Waluigi]