Finishing under threshold

[bmj1]

Hi all,

 

We've got beam and block ground floor, and a 150mm cavity.

 

I'm just figuring out the best way to close the front door threshold:

 

 

Questions:

1) Should I put e.g. 100mm of PIR in the gap ? Should it be wrapped in plastic ? And then fill the remaining 50mm void with concrete ? Should I wrap the concrete in plastic ?

2) I've got some spare insulated board on site (link) - which I could then use to bridge the threshold

3) Are there any other considerations in terms of DPC or drainage ? It's going to be a flush threshold to a raised step in front (not yet built)

4) Any principles I need to apply here ?

 

Thank you in advance.

[nod]

I have a close up of our previous build