Insulation under UFH

[SB2023]

Hi all

We have a concrete slab upstairs and just looking at our UFH. It was a late decision to move away from radiators so we dont have a lot of build up available (78mm in total). Where we are laying karndean this is fine (20mm insulation, 50mm pipes and screed, 8mm Karndean).

But in the bathrooms where we need to allow 25-30mm for final floor (tile and ditra etc), we only have 50mm left.

 

I was considering superfoil underneath the UFH egg crates but I think this is too squishy and likely to cause the screed to crack as it compresses?

 

So therefore thinking of leaving insulation out completely in the bathrooms and accepting a little bit of heat will transfer into the slab in those spaces.

 

Thoughts?

 

Thanks!!

[SteamyTea]

1 hour ago, SB2023 said:

20mm insulation

Is that missing a 0.

 

Rethink radiators.

[SB2023]

its first floor just to be clear. Concrete slab on a metdeck so only reason for insulation is to stop the heat travelling downward into the first floor slab and getting a little wasted there. We were only recommended 10mm but upped to 20mm as Karndean so much thinner.

There is a good chance it will barely ever turn on upstairs as we are so well insulated (ICF, triple glazed etc etc)

We have PLENTY of insulation downstairs and that is all good.

[peekay]

My thoughts are that even if there is no insulation on the first floor, and the heat travels downwards in to the slab, does it really matter? The energy isn't lost, it is still heating the house through the materials under your feet. It might just be a bit slower to react, but if you are running an ASHP low and slow, then the effect will be lessened even further. 

 

If I am incorrect, then please let me know.

Edited May 14 by peekay

[SteamyTea]

26 minutes ago, SB2023 said:

its first floor just to be clear

Right.

Then should be OK.

Will loose about a watt per degree temperature difference, and as you say, will stay mostly in the building.

The MVHR will suck it away and redistributed it.

[SB2023]

Thanks guys. Good point on the MVHR too! I hadnt considered that.

So just ditch the insulation completely then, not worth the risk of an unstable super foil I think.

 

Good to get some validation on this. Never know if you have talked yourself into something in your own head

[saveasteading]

Forget superfoil. Certainly in this context. It depends on adjacent air gaps doing half the work.

Might as well use bubble wrap.

 

20mm of insulation would cause most heat to go up into the room. The waste is still in the house as others say.

[SB2023]

Noted. Super foil is out of my mind!

 

Thanks everyone.

[saveasteading]

1 hour ago, SB2023 said:

Super foil is out of my mind!

It shoudn't be in anyone's mind in my opinion. Their publicity is good. They have their own defintion of insulating performance.

I'd maybe  use it in an attic or shed if it was half price.

I went to a presentation they did. They shouldn't have invited knowledgable people,  and so they concentrated on their other products.

[SB2023]

5 hours ago, peekay said:

My thoughts are that even if there is no insulation on the first floor, and the heat travels downwards in to the slab, does it really matter? The energy isn't lost, it is still heating the house through the materials under your feet. It might just be a bit slower to react, but if you are running an ASHP low and slow, then the effect will be lessened even further. 

 

If I am incorrect, then please let me know.

Yes running ashp too so this also valid and true!

[joth]

If you have any thoughts of using the UFH for cooling then not insulating the upper floors has additional benefit for those loops being effective in cooling the lower floors.

Only snag in my experience is it's the upper floors that over heat first, and the UFH won't be so effective in cooling those but that's true either way.