Minimum dimensional difference between GOK and top edge of finished floor

As part of the building application for our newly planned single-family house without a basement, the planning office commissioned by the general contractor has specified a difference of 35 cm between the planned terrain surface and the top edge of the finished floor. This distance is considered absolutely necessary to prevent moisture problems later on caused by the adjacent soil. Since I consider 35 cm to be relatively generous and this would result in a platform with two steps at the house entrance, I would like to ask whether this large difference could be reduced without causing the moisture problems feared by the planning office.

Note: According to the sectional drawing, the floor structure on the ground floor is such that the base plate accounts for 16 cm and the remaining structure accounts for 19 cm.

If any information is missing to answer my question, please let me know.

I would like to thank you in advance for your efforts.

Best regards

Ralf

If no development plan specifies the arrangement of the upper edge of the finished floor, the requirement of the general contractor (GU) is based on the following: The plaster towards the terrain should generally be executed as a splash water base up to 30 cm, i.e., made with particularly moisture-resistant material. However, the splash water base does not have to be below the upper edge of the finished floor.

According to technical building regulations, all exterior walls in contact with the ground must be sealed against moisture. Only approved seals according to DIN may be used for this; plaster alone is not sufficient. With the specified floor height of 16 cm floor slab and 19 cm floor construction, the height of 35 cm above the upper edge of the finished floor required by the GU is exactly achieved, meaning the exterior walls would no longer be in contact with the ground. Therefore, the vertical seal could be omitted—with respect to the minimum technical requirements at least. It is possible they want to avoid precisely this sealing. I consider the approach of the planner or GU to be unprofessional.

It is correct that, for example, in front of doors, the water-bearing layer must lie at least 15 cm below the openings; however, this can also be ensured by a grate or a drainage channel. Thus, it is technically feasible to create a level entrance.

Furthermore, the thickness of the floor slab of 16 cm seems rather tight to me. For reinforced concrete slabs, minimum concrete coverage over the steel (reinforcement) must also be observed, depending on the location and design of the substructure, 2–3 cm. I recommend having the planning and especially the structural engineering externally and professionally assessed. Additionally, I recommend paying close attention to the horizontal seals during execution.

Regarding the described requirement of the GU, I have the impression that the external vertical sealing is meant to be omitted or a change order provoked. A GU or planner has no right to demand the height arrangement described above from you; it is not necessary with appropriate measures.