WU concrete basement dimple membrane at drainage with dimples for insulation

Hello everyone,

we are currently in the process of completing the basement. The basement was constructed as a WU concrete basement and, due to load case 3 (accumulating seepage water), was additionally coated with a multi-layer bitumen coating according to the soil survey. According to our architect, we do not necessarily need drainage; the "house could even stand in a river" like this.

However, during an on-site meeting, the architect, civil engineer, and structural engineer proposed that drainage should still be installed since parts of the basement, due to the extremely steep slope, may no longer be (affordably) exposed later (8m high embankment with retaining structure). Therefore, the sealing and drainage should be carried out as effectively as possible to minimize potential risks. We agreed to this as it sounded reasonable to us and the additional costs are manageable.

Now we have noticed that the dimpled membrane (drainage membrane with fleece) was installed with the dimpled side (fleece side) facing the insulation. According to the manufacturer's specifications, however, the membrane should be installed with the dimpled side facing the soil for drainage function.

To my understanding, the drainage does not comply with the DIN standard since the surface drainage along the soil-contacting walls was not installed according to the manufacturer's instructions.

How critical do you see this?

Regarding the moisture, I do not see it as critical (WU concrete). However, it is critical that you are paying for a service that is not necessary anyway and which was also executed incorrectly. I would criticize that with the company (i.e. the faulty execution).

The question that arises for me is what happens to the drained water at the base of the basement. Since it is probably not drained according to DIN 4095 (Or was it done after all?), is it ensured that the water does not accumulate again at the basement?

The contractor probably thought that since no drainage is required anyway, it would be better to protect the insulation more. Then it is okay like that. Google: "Noppenbahnen fachgerecht verlegen - bauhandwerk". The article is quite good and covers all variants regarding sealing and protection with [Noppenbahnen].

Regarding the moisture, I do not see it as critical (WU concrete). However, it is critical that you are paying for a service that is not necessary anyway and was also carried out incorrectly. I would criticize the company for that (i.e., the faulty execution).

The question that arises for me is what happens to the drained water at the base of the basement. Since it is probably not drained according to DIN 4095 (Or was it done after all?). Is it ensured that the water does not still accumulate again at the basement?

Yes, a drainage was laid (pipes), which are then backfilled with a gravel layer. As already mentioned, this is not strictly necessary because of the WU and was only installed as an additional measure due to the impossible accessibility after the building’s completion. Therefore, the water at the base is discharged via the drainage pipes.

The contractor probably thought that since no drainage is required anyway, it is better to protect the insulation more. Then it is okay like that. Google: "Proper installation of studded membranes - construction trade". The article is quite good and covers all variants regarding sealing and protection with studded membranes.

Yes, the article states it quite clearly: No drainage pipe = studs facing inward, With drainage pipe = studs facing outward with fleece.

The drainage is basically not necessary because of the WU construction, so it does not matter (for the building) at first. After consulting with the architect and the executing company, however, the studded membrane will now be removed again and laid accordingly facing outward so as not to impair the drainage function (after all, we are paying for it).