It is clear that it does not necessarily have to be the same with us as with the neighbor. As far as I have gathered, the soil conditions were similar throughout the entire construction area. Topsoil on top and then a high clay content further down. It should then be within the range of 3-5?! As far as the contractor has said, the specific description counts for the shell construction. I have noted all differences and inaccuracies (as far as I recognized them) and will insist in the next conversation on recording everything more precisely and mentioning the exact materials. I hope that I am then on the safe side... If he has nothing to hide, that should normally not be a problem. I also have a few people in the future neighborhood who can hopefully provide me with experience values about the contractor.