Parametric Hinterland Urbanism - PROBLEM

Hi all,

new to the forum and to grasshopper.

I am working on a project where we are trying to create a grasshopper file that allows us to study the formal possibility of building within the tight physical and legal parameters of the hinterland (inner-block) areas of european perimeter housing. (Koln, specifically).

However, I've been having a problem with the boolean intersection between 2 capped and union-ed breps. (I approached the problem by defining the lot via the east-west and the north-south sections).

The files have been attached with explanatory notes. Any suggestions on how this might be solved (or other suggestions on how to make the file cleaner/smarter) would be a great help.