Single-family house 150 sqm - Quiet village, space to the neighbors

The ceiling height on the ground floor should be as follows: 2.655m floor height - 0.17m ceiling thickness (assuming that the ground floor and attic floors are at the same level) = 2.485m room height

Based on stair measurements: (14*0.19m)-0.17m=2.49m

So they already have almost 2.5m.

You have a floor height of 2.825m - 17cm floor construction - 25cm concrete ceiling resulting in 2.405m. If the concrete ceiling is now 20 cm then it is 2.455. Does the 17cm on the ground floor already include the floor finish? If not, you can subtract another 2-3cm.

The ceiling height on the ground floor should be as follows: 2.655m floor height - 0.17m ceiling thickness (assuming that the ground floor and attic floor are at the same level) = 2.485m room height

... but rough and not clear.

You have a floor height of 2.825m - 17cm floor construction - 25cm concrete ceiling equals 2.405m. If the concrete ceiling is now 20 cm then it is 2.455.

I am currently looking for a counting rhyme to decide which of your calculations I (do not) follow.

You have a ceiling height of 2.825m - 17cm floor construction - 25cm concrete slab equals 2.405m. If the concrete slab is now 20 cm then it’s 2.455. Is the floor covering already included in the 17cm on the ground floor? If not, you can deduct another 2-3cm.

The dimension +0.00 should be the upper edge of the finished floor on the ground floor; +2.825m is the upper edge of the finished floor in the attic (see plan drawing top view entrance area). Subtracting the ground floor ceiling or attic floor of about 25cm gives: 2.825m - 0.25m = +2.575m. Then subtracting about 7cm (seems rather little = no underfloor heating?) attic floor gives: 2.575m - 0.07m = +2.505m clear height. Plaster ceiling etc. results in approx. 2.48-2.49m (I estimate). I could also be wrong in the calculation right now. But the OP can say something about it.

I am currently looking for a counting rhyme to decide which of your calculations I (do not) understand

In post #9, the planner drew the heights into the views.

282 cm .... but then 14 risers of 19 cm for the staircase are not correct.

In post #9, the planner has marked the heights in the views.

I see 17 cm floor construction, but no raw ceiling thickness (?)