No more ply and wet system UFH sat within joists - efficiency concerns...

[Blimey]

Apologies this is so long winded, but hopefully you're an understanding bunch & you'll stick with the novel and provide a straight opinion on this.

I'm a competent DIY'er (ex-spark), but it's a while since I've done any DIY tiling at home. I'm now re-doing the kitchen floor/walls in a 1960’s house, and having purchased some polished porcelain tiles felt it was a good idea to go for UFH.

The house is well built, crawl space below joists & having researched options (& that it's about 10m2 of UFH, across a 13m2 of tiles) I plumped for a wet system, using a rad conversion kit. This will be sat underneath the existing f-boards, Celotex laid on battened OSB, then spreader plates on top, rather than the biscuit mix).

I then turned to advice on best substrate options above the FB’s & after half day googling this forum and elsewhere, I was headed for using 6mm NMP, given it gets a strong thumbs up on here/elsewhere. Plus the price seems comparable to ply.

To get to the point, it’s dawned on me, that with the above installation and the fact that NMP is an insulator & not a conductor, am I just suppressing UFH output even more by using NMP before tiling?

I get that I can't lay the tiles directly onto the FB’s, but am I right in thinking that whilst NMP is the most stable base for the tiles, is it bad for the UFH? (majority of google results seem to link it with being laid below leccy mats). Some posts suggest NMP can act as a heat store, but I'm a bit sceptical?

So I’d really appreciate the pros opinions if you wouldn’t mind. is NMP still the best option, even with impact to UFH efficiency, or are there alternatives that can provide a solid base & good conductivity?

Don’t want to go for a leccy mat. Not because of bills, but also the fact I've purchased the wet system kit. If an alternate to NMP is a well prepped 12mm ply I could probably live with the height uplift in the floor.

Thanks for sticking with this & look forward to comments & suggestions.

Thanks
Chris

 

[Dumbo]

I don' use nmp myself and what I use wouldn' be suitable for this but you will probably find your floor boards are having more of an impact on heat insulation than nmp.

 

[Blimey]

Thanks JCR. That point had also crossed my mind in the past.

Not that it would be the simplest thing to do, but what flooring would you recommend in lieu of the boards, t&g chipboard or something else?

 

[Chalker]

Just use fermacell gypsum boards, instead of your floorboards. Prime and tile.
Jupiter Systems - Fermacell - http://www.noneedtoscreed.com/fermacell.php

 

[Blimey]

Thanks Chalker. Assume that's a structural board if replacing the floorboards?

would seem to be a good option...

 

[Flintstone]

I don’t think nmp is an insulation really, I am sure I have read somewhere that they help dicapate heat evenly when used in this situation. I’m not sure if that’s no more ply or hardie but there the same make up. I wouldn’t worry about it. I have felt heat come through nmp boards myself over wet ufh

 

[One Day]

In my experience nmp/hardi (silica/cement boards) act basically as you would expect a concrete floor to - it will absorb and conduct heat similarly. You'll be impairing the function of the heat perhaps a little, but not enough to notice it.

 

[Blimey]

Thanks again for these replies. That's put my mind at rest. The only thing I need to worry about now is making sure I plumb the thing in properly.

Using NMP rather that Fermacell will be easier as I've a few sq metres of area that I'm not doing with UFH so the overlay boards will be a simpler solution for the whole area.

Thanks again for all your comments...