Porch extension floor slab DPM to DPC

[Don33e]

Hi All,

I have started our porch extension in preparation to under and gauge the amount of effort prior starting our rear extension. 

The current driveway is a stamped concrete slab, which used to but up against the front door. When removing the section of drive to dig the trench, I have found that there was never any block work below the front door threshold! so rain water over the years has undermined the current porch slab!

I will dig out the old slab, so my question is how best to seal the new DPM to the existing DPC ?

I intend to: 150mm harcore, 25mm sand, DPM, 150mm insulation, DPM, 100mm concrete.

Cheers

Don