Closing internal cavities

What am I supposed to do with the cavities left by removing the walls? They are currently 225mm below dpc.

There is a void underneath the tiles where the screed bridges the gap of 50mm. This is where doors between rooms were

Thanks

Dpm and concrete. I used blackjack dpm and concrete on some shallower ones recently

Thought that might be the simplest option @23vc. Seems a bit pointless trying to squeeze any insulation down there (both slabs have wet UFH). Just make sure continuous DPM!

So I did this job and now have a similar problem with the new bifolds... The existing slab is 150mm short of the track (course of bricks plus 50mm cavity). The existing dpm won't reach the outer leaf though. I've fitted cavity closers vertically but the floor needs to support tiles.


Should I remove the top course of bricks and extend dpm up to bifolds? I assume I would turn it up at the sides and back and fill with 1:5 mix again.