What do I do here? (moved)

Hi all, Hoping people can give me some suggestions on slab set down / drainage beside a slab. Background: I'm planning a reno that includes demolishing a timber framed floor, and then rebuilding on a slab that is approx 650mm below the existing floor level. I've tried to draw it to make more sense. The building is built about 100mm from the side boundary, and at some point over the last 90 years the neighbour has built a wall between the brick piers of my place, and created bit of a...

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