Insulation for wet UFH

[Jimbo123]

Having an wrap around extension built, plan was to have wet UFH (I think the builder is fitting Prowarm system). 
The floor area slab has been poured over foil faced pir, a 100mm board and a 25mm ontop so 120mm in all. Presumably screed will follow. I think this complies with Building regs.
Is this sufficient insulation for UFH ?

I read that this will be about 0.25w/m2k, but there is a suggestion that 0.15w/m2k is required for UFH ?  Is it worth increasing the insulation, and how could it be done as the slab has been poured ?

 

About 1/4 of the new floor area is the old edwardian kitchen floor.  My builder has asked if I want to pay extra and have the old solid kitchen floor dug up to accommodate 75mm of insulation as the old floor has none. Should this be 125mm of insulation to match the surrounding floor ? Or more insulation if possible ?   Help !

I don’t want to have this system laid and then find out its not very effective.

 

Any thoughts ?

Edited April 26, 2023 by Jimbo123
Clarity

[Andehh]

Leave it, for an extension it's fine. It's below average for this specialist /uber passionate forum but for average household 125mm PIR is fine...if slab is poured nothing more you can do anyway. ..

 

 

Edit... Several years ago my folks had UFH installed on 100mm PIR and then 22mm chipboard and 9mm engineered wood. System still worked, just with a slower initial warm up time.

Edited April 26, 2023 by Andehh

[Andehh]

What's the quote to have old floor relaid? I probably would if it has a nothing there insulation wise.... 

[Jimbo123]

Thanks for the reply Andehh

 

£1500 odd for 3.5 x 3.5 metre area.

[Jimbo123]

Thats with 75mm pir

[Andehh]

I would go for that, that'll be a very cold floor otherwise!! 

[Buzz]

Try this calculator to get the estimated u value. 

It will be a lot lower than you think.

i would have the uninsulated part done while your upside down because if you don't do it now you never will .

https://uvaluecalculator.ecotherm.co.uk/calculator/floors/ground floor/solid concrete - insulation below slab/0.3/120/

Edited April 26, 2023 by Buzz

[Jimbo123]

Thanks guys !

[Iceverge]

I'd go for at least 100mm rather than 75mm boards in the floor. There's almost no difference in the price. 

 

150mm while you're at it if you can. You never regret putting in too much insulation.