Hi guys
Went to look at a job tonight, the client wants porcelain tiles 60 x 40cm laid on a kitchen/diner floor 30m2.The floor is half screed half floor boards and wants under floor heating. Any advice on weather to use a decoupling membrane or to lay plywood, and can you lay ufh matting on these products, or any other advice would be greatly appriciated.

Thanks Tony

What m2 is on the floorboard and also the screed.

Hello whitebeam
20m2 is of floorboard and 8.78 is of screed.

I would use 10mm insulation boards making sure they cross over between concrete and wood then decoupling mat then UFH no more than 100w

Thanks barry bp
would you use a single part flexible adhesive to lay the boards and matting.

You will still need an expansion joint between the screed and wood floor.

As above, you must use an expansion joint between the 2 substrates even if you are using a decoupling membrane.

Use 10mm thermal boards, covering the whole floor, this in itself will act as a de-coupler.

lay UFH and cover with SLC

Set a schluter expansion strip in and set out tile from there

use any wattage UFH

100w is only the max on ply

id lay 10mm insulation boards but leave a gap between the two substrates, id then have the ufh on the wooden section run from its own thermostat and not crossing the gap between the two substrates. then lay the ufh over the other section again running it from its own thermostat. slc the ufh cables leaving the gap and then set an expansion joint into the gap and start tiling with a single part flexible addy.
I would also glue and screw the thermal boards on the wooden section and just glue them on the screeded section. id also run a 200w ufh system to make the most of the thermal boards id just laid.

but then thats just me.

is the wooden section even suitable for tiling have you checked ?

Sometimes you use your own experiance to decide best way to do something I personally would not want expantion joint through middle of floor(I know its by the book) i would be confident with insulation boards bracing between subfoors then decoupling mat for more lateral help 100w heatmat warms up more gently and only warms floor 150 and especially 200w is more aggressive and will stress the floor more! 200w is really for rooms like conservatories where thermol losses are high using 2 thermostic controls on thermal boards imo is exspensive and over complicated.I think the finished job would look so much better,you could bare in mind on laying out tiles if pos to make grout joint along subfloor change and when laying heatmat to only have wire at one end so mat runs parallel.This gives you a chance to use silicone joint later(but i dont think you will need it)As i say this is all my opinion and the way i would be happy to do.I know if you ask most people would they be happy with expantion jiont through middle of floor or not they would opt for not .