How much additional cost according to the structural engineer's calculation?

the neighbors partly built without a basement and partly with a concrete basement

At least you already knew that a concrete basement is necessary.

they said they couldn't start with the production planning otherwise.

That would have had the effect for you that you wouldn't have to pay them if you quit. Why do you think you were advised not to accept that?

we don't have it in writing yet but as soon as I have it I will post it

But it does say something in the contract!!! I have already requested this here countless times.

I’ll try again. If you build the [weisse Wanne], then have an expert (who is managing the construction for you) carry out the construction supervision. Just imagine how much can go wrong. It already starts with the planning.

I’ll try again. If you build the white bathtub, then have an expert (who is managing the construction for you) supervise the construction. Just imagine how much can go wrong there. It already starts with the planning.

We do have a construction manager with whom we are very satisfied so far

It says something in the contract!!! I have requested this here from me x times already.

It says something in the contract!!! I have requested this here from me x times already.

Offer
as a single-family house
Plan changes dated 07.01.2023
CreativHAUS Classic 143.1 incl. cellar
 Solid construction "stone on stone" according to Building Energy Act 11/2020
 Exterior house dimensions 10.63 m x 9.23 m
 Roof pitch 36°
 Knee wall 50/100 cm
 Roof overhang 50 cm
 incl. planning (building application) - structural planning – static – energy certificate - awarding
 incl. excavation – drainage – insulation - backfilling
 incl. neutral construction management and site supervision
 Excavation pit statics by client
Note: for excavation pits of 4.00 m and deeper, a verification statics of the excavation pit is required - by client
 Outdoor facilities, terraces, paths, parking spaces etc. by client
 Slope stabilizations, shoring work as well as securing adjacent structures of any kind by client
 Demolition and removal or disposal of structural facilities of any kind by client
 Disposal of unnecessary or non-backfillable excavated material (see construction/performance description) by client
 Costs and services arising from requirements such as building permit, statics, classifications according to earthquake zones and the like by client
 Tile material price €35.00/m² (tile formats from 30 x 30 cm to 60 x 60 cm)
 Wide selection of front door models
 incl. controlled ventilation and exhaust from Viessmann VitoVent 300 with heat recovery
 incl. air-to-water heat pump Vitocal 200 A indoor installation instead of gas/solar
 incl. underfloor heating in all living rooms
 incl. cellar with light shafts according to plan

I just copied this now, it didn’t work otherwise