Apologies for long post: I'm going slowly mad here
We were days from contract exchange, on our SW London Edwardian house, after months of trying to sell - nice, reliable buyers, all ready to roll. They want to build a side-return extension (back of the house) as soon as they complete, before moving in (they are in a rental). They already have an architect.
Neighbour serves party wall agreement last Tuesday - (houses not attached, but they are building within inches of party wall, ie garden wall, as they have already done their side return extension) and puts large spanner in the works.
Basically, our buyer needs reassurance that he can can still build his extension...probably overlapping work on the basement next door (which should take 3 months, starting end of July at earliest).
Party wall surveyor is moving as fast as he can, and he's hired a structural engineer, but both have yet to visit/comment. Surveyor thought the works could run alongside, but he needs the engineer's feedback.
My brother's friend-engineer says basement would force us/buyer to dig ultra deep foundations for extension, unless he backfills with cement - which is, apparently, quite easy and a possible solution - but even if thats true, I have no idea if works can run at the same time.
This is a very long shot, but does anyone have experience in this field, or lived through similar situation?!? Thanks for reading such a loooong post...