Additional sealing of strip foundation with perimeter insulation

Hello everyone,

since our craftsmen have different opinions, I would like to ask you what your opinion/experience is.

Problem:
We are building a house without a basement. Foundation - strip foundations (approx. 80 cm deep). The foundations are insulated with 12 cm perimeter XPS both from the outside and the inside. There are also 12 cm XPS under the floor slab. Since the house is located at the highest point of the new development area, our construction manager thinks we don't need drainage. The construction manager and the carpenter think that the external perimeter insulation does NOT have to be coated with any additional sealing layer. Only as "plaster protection" you CAN lay a dimpled membrane. The plasterer should apply a sealing slurry in the base area and that’s fine. Hmm..... Is that sufficient? Do the XPS boards permanently protect the strip foundations? The window installer says he would definitely additionally coat the foundations with bitumen and pull the dimpled membrane all the way down (80 cm)...
How did you seal your strip foundations (without a basement)?

Is the base slab made of WU concrete?

Is the base slab made of WU concrete?

no, as far as I know - no. It's a standard base slab, nothing special was noted in the offer.

A dimpled membrane does not function as a plaster protection, but as a "backfill protection" in the soil and ends where the plaster begins. Perhaps there was a misunderstanding there. If no waterproof concrete is used, I would indeed recommend black waterproofing to you. In case of doubt, cost-cutting on waterproofing/prevention is done at the wrong point.

It shouldn’t make that much of a difference, there is no basement, and therefore the effort should remain manageable.

Whether this is fundamentally required, I do not know offhand, but if I remember correctly, components in contact with soil should always be waterproofed.

Sealing on perimeter insulation is largely useless (unless you want to install boards that are not moisture-resistant - but why?).

What may be necessary is sealing the strip foundations (i.e., before installing insulation boards), if required according to the relevant water exposure class (ground moisture, occasional pressurized water, etc.) and if they are not inherently resistant (i.e., waterproof concrete construction). Of course, this mainly concerns possible rising moisture from strip foundation to floor slab, and you will certainly have appropriate sealing on the floor slab anyway.

That a strip foundation must be sealed over the entire area would be new to me, however. Therefore:

there is certainly an appropriate seal on the floor slab anyway