Running floor screed across the cavity at a door threshold?

[richard at home]

I'm just about to get the insulation down, prior to getting a liquid screed floor poured.

The wall cavity is exposed where the door thresholds are, so I assume I can lay the insulation across the cavity and screed over, right up to the door, or should I loose fill the cavity to support the foam board where it crosses the cavity?

The insulation is going to be 190mm thick and it will be 80mm where it goes over the cavity. I would only be supported on the inner leaf of the wall.

The insulation is this thick to bring the floor level up to make the finished floor level with the thresholds so there's nothing to trip over.

Sketch shows proposed arrangement. There's a membrane that comes up from under the slab and stops in the cavity. The DPC is directly under the door threshold.

[richard at home]

barryrs said:

Normally the cavity would be filled with weak mix concrete to a level that's around 225mm below DPC so your insulation should sit on top of that.

Heres a standard construction detail.

Thanks Barry, I thought so.

My footing comes up quite high, it's 400mm below the DPC, so the weak mix would come up to within 100mm of the DPC, if it's high enough to support the insulation.

[richard at home]

As I'm having liquid screed over underfloor heating, do I need to run 25mm celotex around the perimeter before I run the expansion foam round? Or is the expansion foam sufficient to prevent heat conducting out to the inside wall?