ᐅ Waterproof concrete + flush-mounted electrical boxes in the basement – how can this be addressed?

Good evening,

We have commissioned a single-family house with a basement from a developer. Three of the four basement rooms will be used as living space or offices.

The basement exterior walls are made of 24cm (9.5 inches) thick waterproof concrete. From the beginning, it was clear to me that in a new build, electrical and network outlets should naturally be installed flush-mounted. Surface-mounted trunking is absolutely unacceptable to me, especially in living areas.

We have discussed this several times with the developer and were always told, “No problem, there have never been any issues with this.” Now, however, the electrician has raised concerns, and the developer is now siding with him.

So, my question to the community: What is the actual risk here? I thought that either the concrete is waterproof or it isn’t.

Are there any guidelines on how deep a flush-mounted box should be installed or other practical experience you can share?

Surface-mounted installation is, unfortunately, a huge no-go for me — which is exactly why we chose a new build, so that my office rooms don’t have to show something like that.

There are also decentralized ventilation units in the basement rooms that require electrical connections embedded in the concrete.

What options are available for this?

Thank you very much!
DR

DReffects schrieb:
We have 24cm (9.5 inch) thick waterproof concrete basement exterior walls.

And that is exactly the minimum thickness needed to make the wall watertight. With waterproof concrete, the sealing depends on the material’s thickness. Waterproof concrete itself is watertight but still vapor-permeable. Will there be any additional layers on the outside? This is important considering the intended use as living space and so on.

There are basically only three options.

1) Run electrical installations inside the basement interior walls.

2) Add an installation cavity on the exterior walls (this has the advantage of significantly improving the concrete look and comfort; however, it should be planned by a specialist because of the vapor permeability of waterproof concrete mentioned above).

3) Have thicker exterior walls built.

Isn't the minimum thickness 20cm (8 inches)?

It depends. Depending on the manufacturing method and exposure class, at least 24cm (9.5 inches) is recommended.

For example, in cases of groundwater pressure and cast-in-place concrete.

@DReffects There are standard and deep flush-mounted boxes. For 1 to 2 cables, standard boxes can be used; for more cables and possibly certain inserts, deep boxes are necessary. Don’t forget cable routing in or on concrete walls.

If there is only one wall per room, consider drywalling and installing the flush-mounted boxes there.

It’s the same for me; I also don’t have flush-mounted boxes in the waterproof external walls. As much as possible, I planned most of the electrical installation within the masonry interior walls. However, only one basement room will become more livable, and there I will probably cover the external walls with Fermacell panels. Some of these panels already have a thinner layer of polystyrene insulation, which is sufficient for standard flush-mounted boxes. There are also baseboard trunking systems where cables can be installed, along with compatible outlets and other accessories, so that everything looks seamless. In an office room, dado trunking channels make sense in certain areas since many outlets, LAN connections, and so on are needed, and a certain degree of flexibility is desired.