UFH - First Floor ideas...

[Mulberry View]

We're building a 200sqm Nudura house, around 135sqm gross ground floor, 230mm PIR over B&B floor. In-screed UFH with around 50mm of liquid screed is looking likely.

 

First floor is just a Master Bedroom, Master Ensuite and a second Bedroom with a small Ensuite, around 65sqm total. We like warm floors in the Bathrooms, so are thinking of going for Roth Clima Comfort mats with 10.5mm pipe over the 22mm Chipboard, their liquid screed over that as it'll make a nice substrate for the Microcement (that SWMBO simply will not compromise on). The Bathrooms are back-to-back and the Posi design is super-rigid.

 

Does anyone have experience of this type of system for first floor?

 

I gather we have to have some sort of emitter in the Bedrooms to qualify for the BUS grant? But we want nice carpets (not limited to 2.5tog), so the option I guess is UFH and just accept the performance loss (the heating will be minimal anyway) or fan coils, but we lose wall area with these I guess?

 

I realise the upstairs heating is debatable for most people, but I don't think we can go for no heating at all up there, I'd hate to have to do something retrospectively.

 

Also, what type of pipe? Roth have quoted for PE-RT (they have an Alu option but say it's overkill), Continal suggest PE-RT/AL/PE-RT....

[MPx]

The current project is an upside down house.  As things have progressed we have gone Passive and won't now have UFH.  However we too loved the UFH on our previous home under a stone floor (downstairs).  At the start of the design for the current I wanted to replicate that stone floor - but upstairs this time as that's where we will be living.  As such it is spec'd to have a Lewis Deck with 50mm screed (something like Kerracol) sat on top of the timber frame Chipboard finish.  The UHF would have sat happily in there if we'd decided to have some.  

 

Last place we had oversize Ali rads upstairs except in the bathrooms where I stuck to wet UFH.  Was a specialist "thin" polystyrene type of carrier with small diameter pipes - all from Wavin.  Make up - 18mm chipboard (wayrock) on the joists, Wavin poly/pipes, 12mm Plywood, Ditra Matting, Ceramic Tiles.   Worked very well for the decade or so we lived with it.

[Nickfromwales]

10 hours ago, Mulberry View said:

Does anyone have experience of this type of system for first floor?

I've installed wet UFH over FF P5 22mm decks many times, and screeded over them; from 'just enough' to ~50mm.

 

I used 16mm Pert AL, never use anything else, as laying UFH is somewhere OTT should be the standard....?  alarm bells are ringing.

[Nickfromwales]

4 hours ago, MPx said:

Make up - 18mm chipboard (wayrock) on the joists, Wavin poly/pipes, 12mm Plywood

Pipes routed into the P5? 18mm is a thin board to compromise.

[MPx]

No Nick.  The wayrock absolutely as standard.  Then the blue polystyrene panels with pipe channels (+pipes) laid on top.  Then the ply, ditra, and finshes. We put an oak "step" in the door thresholds to the en-suites but it was only 38mm and looked like we meant it more than it was a cover up.

[Nickfromwales]

7 hours ago, MPx said:

No Nick.  The wayrock absolutely as standard.  Then the blue polystyrene panels with pipe channels (+pipes) laid on top.  Then the ply, ditra, and finshes. We put an oak "step" in the door thresholds to the en-suites but it was only 38mm and looked like we meant it more than it was a cover up.

Ah, ok, so an “overlay” system. 👍

[saveasteading]

As discussed elsewhere, I have little respect for decoupling mats, . We are going for upstairs being normal chipboard, then egg box overlay with snap-in ufh pipes, then screed. Tiles on top.

 

If it was only for a small area of bathrooms I'd be thinking of electric mats with timers.

 

[Mulberry View]

1 hour ago, saveasteading said:

As discussed elsewhere, I have little respect for decoupling mats, . We are going for upstairs being normal chipboard, then egg box overlay with snap-in ufh pipes, then screed. Tiles on top.

 

If it was only for a small area of bathrooms I'd be thinking of electric mats with timers.

 

 

Egg box overlay? So like this??...

 

https://www.roth-uk.com/products/low-level-overlay-system/roth-quicktemp-climacomfort-system

 

That system has as low as 17mm total build-up when using 10mm pipes at 75mm centres and their fibre-reinforced leveller. Forcrete Microcement could, I think, go directly over this and the 21mm height off the top of the Chipboard would work well with the adjoining carpet/underlay if we go that way.

 

My Ensuite is a reasonable size (around 3.0x3.0)

[Mulberry View]

11 hours ago, Nickfromwales said:

I've installed wet UFH over FF P5 22mm decks many times, and screeded over them; from 'just enough' to ~50mm.

 

I used 16mm Pert AL, never use anything else, as laying UFH is somewhere OTT should be the standard....?  alarm bells are ringing.

 

I agree with that sentiment, I'm the king of overkill, which is why I have 253x145 joists at 400 centres under this bathroom, with a 5m span and strongbacks in there too. It doesn't budge.

[SimonD]

On 20/05/2026 at 11:16, Mulberry View said:

Roth have quoted for PE-RT (they have an Alu option but say it's overkill), Continal suggest PE-RT/AL/PE-RT....

 

16 hours ago, Nickfromwales said:

used 16mm Pert AL, never use anything else, as laying UFH is somewhere OTT should be the standard....?  alarm bells are ringing.

There's hardly any price difference between the two and often I find in bulk I get a better price with the MLCP pipe. The 'overkill' on something so basic when it's a totally unnecessary comment is weird. Personally I'd be going the route of MLCP at the drop of a hat.

[saveasteading]

5 hours ago, Mulberry View said:

like this??.

Indeed. There are lots of versions with more of less plastic/voids.

We have decuded not to put acoustic underlay because our ceilings will do that work, but it's a nice idea. The screed provides density for heat absorption and spread, and also against footfall noise. And the screed is ready for the finish, most of which will be tiles.

 

We are not insulating under it as heat rises, and any going downwards will meet what is coming up through a dense ceiling/floor.

 

 

The downside is that any area without heating (passageways, wardrobes) still needs the same thickness.

[Mulberry View]

59 minutes ago, saveasteading said:

Indeed. There are lots of versions with more of less plastic/voids.

We have decuded not to put acoustic underlay because our ceilings will do that work, but it's a nice idea. The screed provides density for heat absorption and spread, and also against footfall noise. And the screed is ready for the finish, most of which will be tiles.

 

We are not insulating under it as heat rises, and any going downwards will meet what is coming up through a dense ceiling/floor.

 

 

The downside is that any area without heating (passageways, wardrobes) still needs the same thickness.

 

That's all very helpful. My small first floor is designed to have acoustic insulation under it, but I also realise that will block some of the heat rising from the ground floor. I had, however, wondered whether it might be a good idea to add some sort of reflective layer between the Chipboard and the "egg crate" system, what do you think?

Edited 4 hours ago by Mulberry View

[JohnMo]

44 minutes ago, Mulberry View said:

reflective layer between the Chipboard and the "egg crate"

Without an air gap there is zero reflection - if aluminium it just becomes a conductor.

[saveasteading]

17 minutes ago, JohnMo said:

Without an air gap there is zero reflection

Absolutely. This is little understood. In fact there used to be false, or musleadingly vague, assertions about the effect of shiny faces on plasterboard, pir, and that loft wrap multilayer stuff I won't name.

These have now been dropped but the rumour lives on.*

 

It is is still implied that the aluminium layer within an underfloor heating pipe is doing this, but it isn't.  I've burned the plastic off an offcut and found the inner pipe is surprisingly robust, ie not like kitchen wrap. I don't know what it is for.. it helps it hold a shape but also makes it vulnerable to kinking.

 

Back to the question... some of these crates do have pockets of air but I doubt there is much/any benefit in foil.

It's not as if the heat is being lost outdoors or to a neighbour..... it would only heat the ceiling void at worst, and only once.

 

* @Mulberry View do you mind sharing where you heard of this supposed benefit?

 

** I once went to a presentation by superfoil, arranged by the local bco. (It was a short walk and free buffet). I was itching for the pitch on reflective aluminium but he didn't mention it, just another new product which I haven't seen since.

Btw they measured insulation in their own way. I'm not saying it didn't  work,   but bubblewrap is cheaper.

[Mulberry View]

2 hours ago, saveasteading said:

Absolutely. This is little understood. In fact there used to be false, or musleadingly vague, assertions about the effect of shiny faces on plasterboard, pir, and that loft wrap multilayer stuff I won't name.

These have now been dropped but the rumour lives on.*

 

It is is still implied that the aluminium layer within an underfloor heating pipe is doing this, but it isn't.  I've burned the plastic off an offcut and found the inner pipe is surprisingly robust, ie not like kitchen wrap. I don't know what it is for.. it helps it hold a shape but also makes it vulnerable to kinking.

 

Back to the question... some of these crates do have pockets of air but I doubt there is much/any benefit in foil.

It's not as if the heat is being lost outdoors or to a neighbour..... it would only heat the ceiling void at worst, and only once.

 

* @Mulberry View do you mind sharing where you heard of this supposed benefit?

 

** I once went to a presentation by superfoil, arranged by the local bco. (It was a short walk and free buffet). I was itching for the pitch on reflective aluminium but he didn't mention it, just another new product which I haven't seen since.

Btw they measured insulation in their own way. I'm not saying it didn't  work,   but bubblewrap is cheaper.

 

You'll notice from my wording that I said "I wondered". It was a fragment of my own uneducated thought process.

[saveasteading]

9 minutes ago, Mulberry View said:

uneducated thought process.

Not at all. We are allowed logic, hunch and gut feeling. And wondering.

It stops us walking over things that look flimsy, without calculations or test certificates.