Installing drainage after house construction

Hello everyone,

due to pressurized groundwater, this year we have groundwater that has risen above the floor slab and as a result, one side of the house’s exterior wall has absorbed moisture, causing efflorescence inside.

I now want to install drainage myself afterwards. However, I have two questions regarding the planning and execution, and maybe someone can answer them here.

1. Does the drain pipe have to be placed directly below the edge of the floor slab, or can it also be about 1 meter away? The background is that we have a captain’s gable, and otherwise, I would have to install two additional inspection shafts. I have attached a drawing. Please note the left side.

2. While digging, I "found" a pink styrofoam board. In my layman’s opinion, this serves as frost protection for the floor slab. Is this board placed directly against, below, or above the floor slab? Where exactly is it located? To me, it looks as if the pink board lies beneath the floor slab. The real question, however, is where the drain pipe should be placed: above/below the pink board or at some distance from it? I have also attached two pictures regarding this.

Thanks for your help.

Best regards

Dennis

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Welcome to the forum, you are still in the construction phase according to your pictures. I would immediately get an independent building expert to professionally assess all causes and effects and possibly have changes made. You are building without a basement?

Welcome to the forum, you are still in the construction phase according to your pictures. I would immediately get an independent building expert to professionally assess all causes and effects and possibly have changes made. Are you building without a basement?

Unfortunately, we are no longer in the construction phase. The house is already standing with paving, etc. I have to do this afterwards now. And yes, we have no basement.

If you don't have a basement, there is no pressing groundwater pushing through the floor slab. Or is the house situated in a depression that previously and still now serves as a collection basin for surface water from your neighbors or your own roof drainage. In our area, layered water and high groundwater are normal. A popular and cost-effective solution is a vertical drainage pipe with a submersible pump. Drainage pipe 40-50cm in diameter, length up to about 1m below the floor slab. Dig a hole, wrap the drainage pipe with fleece, pour concrete on the ground, backfill with gravel from the outside, put the submersible pump with float switch inside and done.

If you don't have a basement, there is no pressing groundwater pushing through the ground slab. Or is the house located in a basin that used to be and still is a collection basin for surface water from your neighbors or your own roof drainage. In our area, layered water and high groundwater are normal. A popular and inexpensive solution is a vertical drainage pipe with a submersible pump. Drainage pipe 40-50cm in diameter, length up to about 1m below the ground slab. Dig a hole, wrap the drainage pipe with fleece, pour concrete over the ground, backfill from the outside with gravel, put in the submersible pump with float switch, and done.

That sounds good. Thanks for your tip. Since we have a lot of clay soil here and rainwater percolates poorly, your description of your place sounds similar to ours. And no, we can still drain our rainwater via a large drainage pipe from the municipality. The house is also not located in a basin. I probably described it rather amateurishly and mixed up terms. Sorry. Question: does such a vertical drainage then have to be installed at every corner of the house or is one pipe enough?

At our old house, 11x17m, we had done this at 2 diagonal corners. In dry years, the shafts were empty and in wet years, about every 5-10 years, the pumps ran for several weeks, about 1-2 times per hour. That was enough to slightly lower the layer water.