Moisture protection during the construction of basement rooms

Hello everyone,

two basement rooms will soon be underpinning by a construction contractor. The room height is to be increased from 2.15m to approx. 2.65m. Our structural engineer said that if the strip foundation extends 80cm deep from the current basement floor, it would not necessarily be necessary to underpin the basement walls. We have now excavated a small area and found that the strip foundation is only 30cm deep.

That means we have to underpin the entire thing step by step. (Here we are still waiting for the specifications from the structural engineer). In principle, this will probably result in something like in my sketch:



We have received an offer from the construction contractor for the floor structure for 15cm concrete with reinforcement, 10cm insulation and gravel. For the underpinning, the contractor will probably use WU concrete and insert steel cages.

Now I have the following questions:

[*]The basement smells very bad. The outside area of the basement will also be excavated and insulated soon. Then we should at least be “safe” from the outside. What measures could be additionally taken during underpinning to also be protected from moisture coming from the ground? I would like to avoid that possibly the basement walls absorb moisture from below. The contractor says that due to the hillside location water or moisture is not a problem. I would still like to inform myself rather than blindly trust.

[*]Should I insist on a specific type of insulation, since the offer only includes “10cm insulation.”

Nobody any idea or tips?

The contractor said that a drainage is laid under the floor slab, which then leads outside. By the way, what I noticed after we dug down a bit is that in a small area (rather towards the middle of the house, instead of the exterior walls) a small puddle of water appears. (It looks as if around it there are larger stones or very hard clay that is sweating)