Do what someone near me did - buy the house next door and then you are the neighbours. Say OK to the work.
Then sell the house.
That was for a shared drive, but it's the same principal.
You pay how much ?
150 quid in midlands for general 8 yard skip with a door on it.
Put anything in it (not plasterboard of course :lol: ) and pile it up high.
With Severn Trent I was allowed to build foundations down to the load line from the sewer invert, i.e. to a 45 degree line upward from the invert, the idea being that load is transmitted downwards through the ground at 45 degrees.
I had the same thing on my house. The 4 inch solid concrete roof was joined to a mirror image on the neighbours side. I put supports under the roof, then used a petrol stihl saw to cut my roof away from the neighbours as close to the party wall as possible. Then cut the rest of the roof away a...
Its quite normal to have staggered ducting of airbricks, usually where you need to vent a suspended floor under a solid floor. You could use some variant of that.
See (not advertising !)
http://www.manthorpe.co.uk/Building/Products/Through-Wall-Underfloor-Vents/Telescopic-Underfloor-Vent.html...
Cement-based tile adhesive (that you mix with water) is fully waterproof when set, other types (tub mix) are not. If you use stuff that says suitable for swimming tools it must be waterproof, if you think about it.
Having said that, what's wrong with mortar ?
Not quite sure what you mean by "uniform depth" but the substrate does not need to be that uniform, since the bedding mix will take up the space.
You need a recess a bit deeper and wider than the frame that takes the cover. Just bed it down onto a dryish strong screed mix (including sharp...