Cost effective floor decks for wet UFH

[allthatpebbledash]

What’s the most cost effective way to have ground and first floor decks installed?

 

The project is a retrofit as that would be the word best describing it. Not chasing numbers. Except the current shell as it stands is the only existing thing remaining, everything else is being replaced.

 

The current floors are suspended timber decks. There is a void of approx 500-900mm as the site slopes a little. Both are being taken out as knackered.

 

The walls outside will be having EWI. A new well insulated roof is being installed. The question is, what type of insulated floor is most effective and cheaper to do relatively?

 

The plan is for UFH on both floors. We think the wet overlay type upstairs, but would it better to have wet in screed downstairs? On what joists, timber? Posi? Lewis deck? 
 

It is unlikely to make this a ground bearing slab as lots of void to fill and site is on clay.