UFH - Why is Plywood needed & Transition

[GlanMenai]

Hello! 

 

Can anyone with a bit more knowledge than me guide me on this? 

 

We have a room that will be half tiled, and half floating floor - we are planning on having (water) UFH installed by using those panels that have the pre-channeled grooves into them for the pipes (similar to LoFlo Lite) 

 

Currently we have 22mm P5 Chipboard down, across the whole floor. My understanding is that, as per the instructions, if anywhere is to have tiles on top of the UFH, then those boards need to be structurally secured to the ground - as the above .pdf states: 

 

Quote

For tiled or levelling compound installations you should install a structural plywood for new floors or for existing floors
you may need to overlay these with a suitable thickness of plywood or cement boards, which should be fully screw down
at 150mm intervals.

 

The P5 Chipboard won't take any adhesive, and so I imagine that's why the plywood needs to be laid down, so we can glue and screw the UFH panels down. 

 

I have two questions:

 

1. What I don't fully understand is why do we need to secure the UFH Panels down for the tiled area? What difference does it make if we don't? Is it to stop movement/cracking in the tiles? 

2. How do I deal with the step from plywood to non plywood area? This transition will be in the same room (it's on open kitchen to living room) and the other side of the room will be a floating floor. I'm just trying to save some money by not having the whole area needing plywood. 

 

So if anyone can explain to me why the need of the Ply is there, that would be ace, and if there is any way of doing this with a transition between the two areas? 

 

Many thanks!

 

[Temp]

2 hours ago, GlanMenai said:

We have a room that will be half tiled, and half floating floor

 

Just checking..  So the whole floor is currently P5 chipboard over wooden joists.  To which you want to add UFH and then half will be tiled and the other half will have a wood finish?

 

Tiles need a near rigid substrate  because any flexing can cause problems such as cracked tiles or cracked grout. It's commonly recommended to overboard existing floors with plywood or cement board screwed down at 150mm intervals to improve the rigidity. On really old floors with undersized joists more work might be required. Especially if you plan to tile then put a heavy kitchen on top.

 

The foam UFH overlay board foam boards dont provide much/any extra rigidity themselves so the existing floor must provide the rigidity needed for tiles.

 

I would ply the lot or put ply where the tiles will go and a cheaper board of the same thickness where the wood floor will go. 

 

How much insulation is under the chipboard? Ideally you need at least 120mm and many will recommed 200mm. We only have 80mm and wish we had more. 

 

 

[GlanMenai]

Hey there @Temp!

 

Thank you for your reply, that makes perfect sense, so it's just to make the floor under the tiles a bit more rigid, to avoid flexing & cracking on the grout/tiles. 

 

What would the cheaper board of the same thickness be in this case you think? I'll have a chat with the guys at the local merchant to see if there's something that I can use for the rest. 

 

We have 120mm insulation between the joists, so hopefully that'll be ok!

 

Thanks Temp, appreciate the help.