UFH and underlay

[Walshie]

Hi,

Screed is down and dying out.

I have wet UFH in 50mm of anhydrate screed. I plan to use engineered timber flooring.

 

I’ve had the screed sanded to address laitence etc.

 

The question I have is whether to lay underlay, or bond directly to the screed.

 

I have been advised that underlay will impair the efficiency of the UFH?

 

I’d appreciate your advice please?

 

Thx

 

 

 

 

 

[JohnMo]

4 minutes ago, Walshie said:

have been advised that underlay will impair the efficiency of the UFH

For UFH you should be bonding the flooring to the screed. An underlay acts as insulation 

[RedSpottedSev]

Would you advise against decoupling membrane for porcelain tiles flowing throughout over 85m2? I worry about cracking, but not sure how insulating decoupling membrane is

[Thorfun]

11 hours ago, JohnMo said:

For UFH you should be bonding the flooring to the screed. An underlay acts as insulation 

I don’t think it’s as black and white as this. For a well insulated airtight house there’s no need for high flow temps and using underlay suitable for ufh in areas with engineered timber flooring will work. Even if it did reduce the temperature a bit the whole house would have the same temperature and so other areas would compensate. 
 

we have underlay with our engineered flooring in some rooms and tiles elsewhere and our house is not cold.

 

2 hours ago, RedSpottedSev said:

Would you advise against decoupling membrane for porcelain tiles flowing throughout over 85m2? I worry about cracking, but not sure how insulating decoupling membrane is

we also have decoupling membrane under our porcelain tiles and can feel the tiles are warm when the heating is on and the flow temperature is high enough. Our current flow temperature is 26 deg C and the house is maintaining 22 deg C but the tiles aren’t warm. They’re just not cold. 

 

It’s very easy to overthink things! I’m an expert at it.