New extension adjoining neighbours walls

[burt12345]

Hi, I'm about to start building a single storey extension full width on the back of our house in ICF (Insulating Concrete Forms).

Our neighbours property protrudes ours by about 0.5m which we will butt up against. They also have a room that is mostly below our ground level, the space between that roof/retaining wall and the party (what used to be a short garden wall 2ft high) wall is backfilled with rubble with a concrete slab on top.

Please see photos for hopefully a better understanding.

We have a ring beam & slab ready that doesn't have any dpm, this will go on top and up our new inner wall.

The ICF blocks will be filled with concrete with a waterproofing additive to above neighbours lower roof level. We will have a vertical dpc off our wall.

Do I need to be damp protecting our neighbours wall with anything before butting up to it? Do I leave any gap, or would it be better to fill the void?
Do I need to need to "sort of render" the rubble under their spanning slab, and protect that too?
If so, should I be using bitumen paint or adhesive sheeting, or something else?

Many thanks

Burt

[attachment=1]partywall1.jpg[/attachment][attachment=0]partwall2.jpg[/attachment]

[welsh brickie]

I would paint the wall with buitumin,and build it tight against the wall.