ᐅ Is it necessary to waterproof the interior of a concrete slab with a bitumen membrane?

Good evening,

I have a question regarding the waterproofing of the concrete slab.
Is it always necessary to waterproof the inside of the slab with a bituminous membrane?
I often see unfinished buildings where the plumbing and electrical installations are placed directly on the raw concrete floor (so no bitumen underneath).

Our setup is as follows:
- Geotextile
- 60 cm (24 inches) foundation cushion
- Blinding layer
- 12 cm (5 inches) insulation
- 22 cm (9 inches) concrete slab
Later, there will be an additional 20 cm (8 inches) floor build-up.

Can anyone provide some input on this?

Whether and where waterproofing is necessary depends on its required function: the floor slab can be sealed underneath (with a membrane or by other means) against, for example, rising ground moisture; therefore, this waterproofing will no longer be visible later.

It is then only necessary to protect the floor build-up layers against residual moisture from the floor slab itself, which can be done at a different level.

On my building permit / planning permission, there is a wall damp-proof membrane at the edges, and everything else is placed directly on the concrete slab. In addition, the first row of exterior wall blocks was made with 24cm (10 inches) blocks instead of the usual 42cm (17 inches), and the joint between the floor slab and the first row of blocks was sealed. XPS insulation is applied in front of the foundation wall.

There is also a thin sheet of film between the insulation and the concrete slab.