Laying UFH over ply board?

[Element]

First time with UFH, customer has existing chipboard floorboards but wants a ply board on top then electric ufh mat and tiles on top. Is this a good idea? Had conflicting advice from my local tile supplier over this issue... The ply is to be screwed down to the chipboard. If the UFH heats (and thus inevitably expands) the ply - even with flexi adhesive - would you expect a problem?
Thanks in advance....!

 

[Ian]

An insulation board/cement board would both be better options than the ply, insulation boards will help the heating system run more efficiently as well.

 

[White Room]

What tile is being fixed..

 

[Element]

It's a heavy slate tile to be fixed... I feel it's a right move to lay the ply over the chipboard (to prevent the slight movement in the floor) but adding in an insulation board on top would raise it too high for the meeting of the adjacent room...

 

[White Room]

As Bri and some slc on the ufh mats...

 

[Uheat - Keith]

Same as Bri.
Notes from our quotations always say: 'Onto a load bearing base the 6mm or 10mm insulation board will need an overall extra thickness of 8mm or 12mm: 6mm or 10mm board with 2mm powder flexible tile adhesive under the boards to fix.'
If you went onto Ply, 100w/m2 system is used.
If your had the cement insulation boards, you can then go up to a 160w/m2 or a 200w/m2 system.
Tiles, Stone, Slate etc is best with 160w/m2 as a minimum.
Warm regards,

 

[Rich]

Bang on advice above as per usual :smilewinkgrin:

 

[Element]

Many thanks for the advice

I haven't been in here for ages - used to last yr but then work virtually dried up, picking up a bit now so no doubt I'll be back in with more questions :smilewinkgrin: