White tub - additional vapor barrier?

Hello dear ones. Our floor slab is finished, the interior walls almost as well, and preparations are underway for the hollow wall elements. Execution of White Tank. Included in the specifications from the general contractor: The floor slab will be made of reinforced concrete according to the static calculation, with a minimum thickness of 25 cm in waterproof concrete of concrete quality C 25/30. Additionally, on the floor slab, a waterproofing against ground moisture and non-accumulating seepage water according to DIN 18195 will be applied as a bitumen waterproofing membrane or an equivalent product of the contractor's choice. The exterior basement walls will be constructed from double wall elements. The walls consist of two-shell precast concrete parts of concrete quality C25/30 with a total thickness according to the drawings (minimum however 25 cm) with reinforcement according to the static calculation in accordance with DIN 1045. The cavities will be cast on site with watertight in-situ waterproof concrete of concrete quality C 25/30, with the advantage of a jointless concrete core. The butt joints of the individual wall elements, as well as the transitions from the floor slab to the walls, will receive joint tapes or suitable sealing elements (manufacturer Mastertec or Pentaflex). The exterior walls will receive perimeter insulation made of XPS rigid foam boards with thickness according to KfW 55 calculation.

Now the basement is partly heated and separated from the cold basement by a 30 cm thick Poroton wall. In the heated part of the basement there is the utility room, a shower bathroom, and a guest room that is occupied 1-2 times a year for 2 weeks each time. Ceiling height 2.20 m. The basement is not declared as living space. Therefore, our general contractor also believes that no vapor barrier needs to be installed (bitumen coating or other coating). There are many opinions on the internet. Even my construction supervisor is torn.

What do you recommend? Should I additionally coat the basement wall surfaces with bitumen? Or better to plaster? Can something like this be done by oneself? I cannot plaster but I can paint. A sealing company said in my case a bitumen coating would be sufficient, since it is only about the vapor barrier. He would charge €19 per square meter. That would cost me €1615 for 85 m². With self-purchased material (e.g. Webertec 901) about €150 - 200 in material costs.

What do you think?

I believe that your general contractor is responsible for proper execution. Even if you deceive the building authority regarding the living area, your general contractor is well aware of what he is supposed to build

Bauexperte von unterwegs

Nobody cheats anyone here. If anything, the general contractor shirks work that he should do in my opinion. Nothing of the sort is stipulated in the contract.

Nobody is cheating anyone here.

And does this, your statement from post #1, mean anything different than that in your BV the size of the living area was somewhat adjusted?

In the heated part of the basement, there is the utility room, a shower bath, and a guest room which is occupied 1 - 2 times a year for 2 weeks each. Ceiling height 2.20m. The basement is not declared as living space.

Rhineland greetings

Was the sealing done correctly? :
The base slab as well as all the joints were primed with bitumen primer undiluted instead of 1:10 with water - using a roller. After a drying time of about 1-2 hours, the transition from slab to walls and the joints were filled with fabric and thick-layer coating.
I am concerned about the undiluted primer.
According to inquiry with the expert, it should not be a problem. When inquiring with another sealing company, it was said to be problematic because undiluted on waterproof concrete adheres poorly.

with "unvernünftig" was meant undiluted. "stupid phone - with autocomplete"