yup JD has it. We allways put a vertical DPC tray on the new builds to facilitate level threshold with FFL and outside as its what people want.
This... cavity tray to protect inner skin from damp releasing any water that gets behind outer skin through weep holes... I have also sometimes seen a second dpc 150mm above.
The paving above probably would be ok with standard cavity wall if it was built right. Only problem the bricks above the paving would now be normal housebricks laid with a weak mix not engineering bricks laid with strong 3-1 mix so susceptible to saturation and frost damage from rain splash.
Obviously if solid walls as I’m assuming above it’s not a great idea... But could be far less of a risk if detailed correctly.
I’d be checking the channel drain installation first, if it is butted against the house it’s likely no concrete/mortar is between brickwork and drain channel. You could lap a wide dpc in an L under the channel and concrete bed and up the wall before setting the channels. They don’t seal together well and water tends to sit in them once crap builds up possibly leaking and pooling against the wall before it gets to the outlet.
I’ve seen some shocking jobs, channels set on spots, slot drains with no access, channels roughly mitred in corners and barely connected.
Takes time and patience to get them right.
If paving has to fall back to the house then I usually lay one row of paving falling away from the house say 600mm then instal slot drain then paving falling back to house. Makes life far easier getting drains in if the house was trench fill...
