Floor Insulation - Help needed

[Darren T Archer]

Morning
We are building a new house, we have a bit of an issue / query for the floor construction and was wondering if anyone had come across it had a solution.
Basically the ground floor will be a solid slab with underfloor heating. So we have a finish which is a 75mm reinforced screed. But we want to get 300mm of insulation into the floor and are wondering where its best to put it. Has anyone put 300mm of insulation under a floor screed. I'm just worried about the potential of crack due to compression and movement of that much insulation.
I'm thinking the best solution is to have 200mm insulation then a floor slab then 100mm of concrete followed by the screed.
Any help much appreciated. Confused

[Peter Starck]

Hi Darren
I used an insulated reinforced concrete slab in my build. It was supplied by Isoquick and has 300mm thick base insulation and 200mm thick upstand insulation. The reinforced concrete slab is 200mm thick. I don't have underfloor heating but I would have thought a 150mm concrete slab with 50mm self levelling screed would be OK.

[Nigel Murray]

Look at
http://viking-house.co.uk/passive-slab-insulated-foundations.html
no problem

[Nick Grant]

I'd consider putting the pipe direct in the slab but with these levels of insulation I assume the building is Passivhaus. This means you won't want the floor to be warm, just a degree or 2 above room temperature but that's another discsussion that I think is somewhere on the forum!

Nick