Question regarding underfloor heating layers

[Nanda]

Hi,

 

I have recently taken a house and trying to get wet underfloor heating installed (combi boiler based). I have very less knowledge of the building methods or construction methods so please excuse my ignorance with regards to the question. The house currently has laminate flooring with concrete layer underneath. I'm trying to get porcelain tile based flooring with wet underflooring.

 

My builder has started off the process. The laminate flooring has been taken off now. And he has almost finished drilling off the floor. I can see gravel flooring now. As per my builder this is going to happen next....1) Preparatory work: Remove all the rubble, level off the current uneven gravel floor by taking off the sharp items. 2) Place insulation boards all over the flooring (50mm thick) 3) Then place the hot water piping, etc. 4) And then the concrete, screed and placing tiles.

 

So I have just got a few questions with regards to steps 1 and 2 - I have been seen / read at multiple sources that a screed / concrete layer needs to go in first even before the insulation boards are fixed. This is probably to hold the boards secure(?). So, I'm now a little worried if there is a flaw with what my builder is doing.

 

So, just wanted to see if my concerns are valid or not. Please help.

 

Thanks

[SteamyTea]

8 hours ago, Nanda said:

Place insulation boards all over the flooring (50mm thick)

That really is not enough.  Not even sure it would meet building regs.

[JohnMo]

I think and someone will correct me.

 

Blinding sand

DPM.

Insulation, on DPM and up the wall. (25-50mm up wall).

If using aluminium faced board, a polythene interface layer.

UFH pipes

Concrete floor.

 

As said 50mm insulation is not enough.  If you can 150mm that is better.  Otherwise the heat will travel down as much as upwards.

 

 

 

[Russell griffiths]

Waste of time, don’t do it. 

Insulate the floor as much as you can and fit radiators, ufh will be very expensive to run if your heating the ground beneath your house. 

[Nickfromwales]

Get a new builder immediately!!!!!!

50mm of insulation is not even building regs, so this chap is WAYYYYYYY behind the times and not up to the task. If you put anything less than 140-150mm of insulation under a HEATED floor, you're going to have very poor results with the heat output, plus the running costs will be very high. 

I would also have a guess that the other aspects of the building are leaky and poorly insulated, so the space heating demand will be adversely high. That is not well suited to UFH as it runs at very low temps and cannot be turned up beyond 27oC floor surface temp without the home becoming uncomfortable.

This sounds like a disaster unfolding, sorry, but good you have registered here and are asking the right questions  Stop this work now, before it's too late to change it.  

[Temp]

We have 80mm insulation and wish we fitted more. If building again I would go for 150mm or more. On a retrofit 100mm might be OK if there are height issues but not ideal.

 

Some BCO insist on a structural concrete slab under everything but if you have well compacted hardcore I don't think its needed

 

Ufh in screed

Poly sheet to retain water in screed

Insulation

DPM

Sand blind

150mm well compacted hardcore.

 

If the hardcore is very coarse I'd suggest putting a finer layer on top and compact again.