ᐅ WU concrete basement with dimpled membrane for drainage and insulation

Hello everyone,

we are currently finishing the basement. The basement was constructed as a waterproof concrete (WU concrete) basement and, due to load case 3 (rising seepage water) according to the soil report, it was additionally coated with a multi-layer bitumen seal. According to our architect, a drainage system is not strictly necessary; the “house could stand directly in the river” like this.

However, during an on-site meeting, the architect, civil engineer, and structural engineer suggested installing a drainage system after all, because parts of the underground level will become inaccessible (and unaffordable to expose) later due to the extremely steep slope (8 m (26 ft) high retaining wall). Therefore, waterproofing and drainage should be carried out as thoroughly as possible to minimize any potential risks. We agreed to this, as it sounded reasonable 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 instructions, the membrane should be installed with the dimpled side facing the soil for proper drainage function.

From my understanding, this means the drainage does not comply with the applicable standards (DIN), since the area drainage along the earth-contact walls has not been installed according to the manufacturer’s guidelines.

How critical do you see this issue?

Regarding moisture, I don’t see it as critical (waterproof concrete). What is problematic, however, is that you are paying for a service that was unnecessary in the first place and, on top of that, was executed incorrectly. I would raise this issue with the company (specifically the faulty execution).

The question that arises for me is what happens with the drained water at the base of the basement. Since it is probably not being discharged through a drainage system according to DIN 4095 (or was it done after all?), is it ensured that the water does not accumulate around the basement again?

The contractor probably thought that since no drainage is required anyway, it would be better to provide extra protection for the insulation. In that case, it is acceptable as it is.

Try searching for: "proper installation of studded membranes - building trade."
The article is quite good and covers all variations regarding waterproofing and protection using studded membranes.

Cronos86 schrieb:

Regarding moisture, I don’t see it as critical (waterproof concrete). What is critical, however, is that you’re paying for a service that wasn’t really necessary and was also performed incorrectly. I would address this issue with the company (specifically the faulty execution).

The question I have is what happens to the drained water at the base of the basement. Since it probably isn’t being discharged through a drainage system according to DIN 4095 (or was it installed after all?), is it ensured that water won’t still accumulate around the basement?

A drainage system was installed (pipes), which will be backfilled with a layer of gravel. As mentioned before, this isn’t strictly necessary because of the waterproof concrete but was added as an extra measure due to the impossible accessibility after the building is completed. The water at the base is therefore discharged through the drainage pipes.

Tolentino schrieb:

The contractor probably thought that since drainage isn’t required, it’s better to provide extra protection for the insulation. In that case, it’s acceptable.
Try searching for: “Proper installation of dimple membranes - construction trade.”
The article is quite good and covers all options regarding waterproofing and protection with dimple membranes.

Yes, the article clearly states: no drainage pipe = dimples facing inward; with drainage pipe = dimples facing outward with filter fleece.

Since the drainage isn’t basically necessary due to the waterproof construction, it doesn’t really matter for the building at first. However, after consulting with the architect and the contractor, the dimple membrane will now be removed and reinstalled with the dimples facing outward to avoid impairing the drainage function (after all, we are paying for it).