ᐅ Older Building / Strip Foundation - Site Plan, Water, Clay Soil, Drainage
Created on: 27 Jul 2025 13:45
R
rschramlHello,
I have read many posts on this topic in the forum, and there are different opinions depending on the situation. Therefore, I would like to ask for your opinions regarding our basement project.
We have started renovating the basement. Previously, the soil (brown clay) between the strip footings had about 10cm (4 inches) of concrete on some gravel. We never had water in the basement, but there were one or two spots where damp base areas could be seen during heavy rain. Before starting the renovation, I made a pit in the basement where water accumulated during heavy rain, but it never overflowed.
Our house has a newer extension (also on strip foundations) that is 70cm (28 inches) deeper and we have repeatedly had problems there during heavy rain. The drainage there could not carry the water away, and it pushed water inside. However, it did not affect our basement, which is higher.
We have now excavated our basement down to the bottom edge of the strip foundations, and with the current rainfall amounts, water is being pushed under the strip foundations into the basement. It is currently kept dry only by pumping. The drainage in the lower part of the house is currently not having any problems, and it seems to me that less water arrives there.
Execution question:
The next step is to install the concrete slab (20-25cm (8-10 inches) watertight concrete with reinforcement; afterwards, the edge areas will be sealed with epoxy resin). The builder suggests installing a drainage system under the slab with a soakaway pit and pump so we can pump the water out. This means placing drainage along the exterior wall but on the inside under the slab where the water is pushing through, then backfilling with gravel, including about 5cm (2 inches) of lean concrete layer before the slab is poured.
I keep wondering if this makes sense. With the drainage and lean concrete layer, I would have a capillary-active layer exactly where the water is pushing in.
Would it perhaps be better to pour clean concrete all the way to the bottom edge of the foundation without a lean concrete layer or drainage, so that the water is effectively “blocked” or pushed away as well as possible?
Doing anything from the outside is almost impossible.
What do you think, or what are your experiences? Attached are some pictures.
I have read many posts on this topic in the forum, and there are different opinions depending on the situation. Therefore, I would like to ask for your opinions regarding our basement project.
We have started renovating the basement. Previously, the soil (brown clay) between the strip footings had about 10cm (4 inches) of concrete on some gravel. We never had water in the basement, but there were one or two spots where damp base areas could be seen during heavy rain. Before starting the renovation, I made a pit in the basement where water accumulated during heavy rain, but it never overflowed.
Our house has a newer extension (also on strip foundations) that is 70cm (28 inches) deeper and we have repeatedly had problems there during heavy rain. The drainage there could not carry the water away, and it pushed water inside. However, it did not affect our basement, which is higher.
We have now excavated our basement down to the bottom edge of the strip foundations, and with the current rainfall amounts, water is being pushed under the strip foundations into the basement. It is currently kept dry only by pumping. The drainage in the lower part of the house is currently not having any problems, and it seems to me that less water arrives there.
Execution question:
The next step is to install the concrete slab (20-25cm (8-10 inches) watertight concrete with reinforcement; afterwards, the edge areas will be sealed with epoxy resin). The builder suggests installing a drainage system under the slab with a soakaway pit and pump so we can pump the water out. This means placing drainage along the exterior wall but on the inside under the slab where the water is pushing through, then backfilling with gravel, including about 5cm (2 inches) of lean concrete layer before the slab is poured.
I keep wondering if this makes sense. With the drainage and lean concrete layer, I would have a capillary-active layer exactly where the water is pushing in.
Would it perhaps be better to pour clean concrete all the way to the bottom edge of the foundation without a lean concrete layer or drainage, so that the water is effectively “blocked” or pushed away as well as possible?
Doing anything from the outside is almost impossible.
What do you think, or what are your experiences? Attached are some pictures.
We are not familiar with your house and therefore can hardly interpret the images provided.
Please read up on underpinning and discuss the project with a structural engineer as well. You don't want it to end up like "mission accomplished, patient dead." Proper planning is essential here, regardless of how daring you feel.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
rschraml schrieb:
We have now excavated our basement down to the underside of the strip foundation
Please read up on underpinning and discuss the project with a structural engineer as well. You don't want it to end up like "mission accomplished, patient dead." Proper planning is essential here, regardless of how daring you feel.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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