Build a terraced end house with an additional unit (GÜ) on your own

Today I was informed by the GÜ that the structural engineer threw the foundation proposal at the geotechnical expert. That would never hold with the L-shaped stones.

Today I was informed by the general contractor that the structural engineer completely rejected the foundation proposal to the soil expert. It would never hold with the L-bricks. There is also the risk that in case of a later underpinning, everything would slide away. It would be as if the expert had not considered that at a later time there will be a boundary construction on one side.

Our general contractor is now working with the structural engineer on a cost-neutral alternative, which they apparently have already found. Today or tomorrow there will be information on how the foundation will be done.

The start of construction must be strictly met by 01.10.

What is the cost-neutral idea supposed to be? I can't think of anything! I can already see that the alternative will only work with the help of the neighbor.

Cost-neutral to the 15k for the fill. It will probably be a foundation solution that goes down to the neighbor's future basement depth.

Foundation at the neighbor's basement depth? What happens to the space between the foundation and the top edge of the finished floor? I just can’t imagine how to realize this without lowering the ground floor. Your general contractor can’t work magic either. Or maybe he can

How do they know how and where the neighbor wants to found his basement? Maybe he wants 2.60m ceiling height there...