…and that’s how you end up with an embarrassing four-centimeter curb into what was supposed to be a level-access shower. Drop the structural concrete slab under the wet rooms by twelve centimeters on your shell plans. Not five. Not "coordinated on site later." Twelve. If you let the engineer pour that slab dead flat across the whole floor plate, your clearance for acoustic insulation, slope screed, and the drain body simply evaporates. You either raise the finished floor of the entire apartment by two inches to compensate, or you accept the step. Get it onto the formwork drawing before the rebar is tied. It is the single cheapest line you will ever draw.