UFH over a CLT floor

[Nick1c]

We plan to put some pipe work in for underfloor heating/cooling on out first floor. It is a 160mm thick slab of CLT & the ffl needs to be 70mm above it, my plan is to fit 48mm batten to it at 400 centres, fit 20mm of insulation between them with pipes & kiln dried sand to the top of the battens, cover it with 6mm ply which will form a working floor for boarding out & decorating & then a 15mm engineered wood to finish off. 
The reason for the insulation is twofold - to help with impact noise (I am not sure how effective this will be) & to reduce the weight on the floor. 
Is there a better &/or more cost effective solution? There will be a suspended ceiling (fermacell) below. 

[Onoff]

What about 50mm of PIR then 22mm of something like ProWarm or AmbiChipBoard pre routed chipboard?

 

Or would a light aggregate, sand cement mix be better for sound deadening?

 

@ProDave on here did some sort of biscuit mix upstairs I think.

 

[ProDave]

Yes my heat spreader is dry mixed sand / cement. It dries hard but does not have much strength and can snap easily hence it is often called "biscuit mix"

 

25mm battens are all you need with the pipes in between and 25mm if biscuit mix.  Engineered flooring spans between the battens, I used 20mm thick engineered flooring. Is 15mm thick rated as a structural floor?

 

 

[Nick1c]

Thanks. 
@Onoff my suspicion is that the pipe work will be most useful for cooling so I am trying to increase the heat capacity of the floor, I think sand/biscuit mix will give a better & cheaper result than the pre-routed boards. 

@ProDave was there a reason you used biscuit mix rather than just sand?

I will check if we need a structural floor - the battens will be fixed to 160mm CLT, which is unbelievably solid. 
There is a lot of the 48x48mm batten on site atm which is why I am planning to use it. We are having shadow gaps rather than skirting so the boarders need an edge to work to, the 6mm ply provides this & allows the painting to happen before the floor needs laying. Another option would be to use 25mm batten with ply & 22mm floor over it - but would this act as too much of an insulating layer?

[ProDave]

I had never heard of just using sand.  I thought biscuit mix was the accepted norm for this type of heat spreader.

 

You need to check if your floor can take the extra dead weight of 48mm od biscuit mix if choosing that depth.

 

Surely you need the finished floor before boarding to do shadow gaps? 

[Nick1c]

If I use the 48mm batten I planned to put 20mm of eps/pir under the pipes to reduce weight. 
The ply would give both a straight edge for the boarders to work from & also a working floor for painting before the floor finish went down. 
If I use 25mm batten there will be 30-40mm of wood over the pipes, dependent on the minimum I need for the slider threshold & windows that run to the floor. 

[Onoff]

52 minutes ago, ProDave said:

I had never heard of just using sand.  I thought biscuit mix was the accepted norm for this type of heat spreader.

 

You need to check if your floor can take the extra dead weight of 48mm od biscuit mix if choosing that depth.

 

Surely you need the finished floor before boarding to do shadow gaps? 

 

There's a few lads on the US solar forum use plain sand for heat storage.

 

There used to be a mix we came across on commercial roofs that was always termed "light agg", light aggregate was what I took it to be. Futher reading suggests this was expanded clay balls called Lytag. Roofs were laid to falls on the stuff and it was often really, really thick. It was laid on top of the structural slab and before the asphalt. I always wondered if it had insulating properties because of the air gaps.

 

This:

 

https://www.specialistaggregates.com/lytag-fill%C2%AE-814mm-aggregate-p-2330.html

[Nick1c]

I think I am going for a compromise - 38mm batten @ 538 centres, 10mm eps, sand/biscuit mix, 12mm ply. It gives me an optimal ffl, uses easily available materials (standard sized sheets of eps are hard to find, much easier to get EPS designed for EWI in 500’s) & a solid working floor. With 15mm engineered boards on top there will be 27mm of timber to impede heat transfer, but hopefully not too much. I am erring towards using sand as the benefit of dry mix in this situation isn’t obvious to me. 

 

Just seen that Wunda have opened!!