ᐅ New Construction with Basement | Waterproof Concrete plus Perimeter Drainage
Created on: 5 May 2021 10:55
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Hotdogxxxx
Hello knowledgeable people,
We are planning to build a new house with a basement. According to the soil survey, the ground up to a depth of about 5 meters (16 feet) consists of impermeable glacial till. Below that is permeable sand. There is no problem with rising groundwater here. However, due to the soil, surface water can be directed towards the basement wall.
The expert says the basement could be constructed either with masonry and drainage boards on the walls or with waterproof concrete. For masonry, a perimeter drain with a sump pit should be considered. If waterproof concrete is used, the expert states that no drainage is necessary.
The construction company recommends a masonry basement with waterproofing against hydrostatic pressure and perimeter insulation boards. Additionally, a perimeter drain and a sump pit should be installed. Alternatively, they suggest using waterproof concrete with open water management. However, they generally still recommend a perimeter drain with a sump pit for waterproof concrete to avoid long-term problems.
These measures/recommendations would increase the cost of a masonry basement by about €17,000 and for waterproof concrete by €7,000 with open water management or €16,000 with perimeter drainage and sump pit.
Basically, we would lean towards using waterproof concrete, but the recommendation to still install drainage seems a bit like a double safety net to us. The construction company justifies this because of the hydrostatic pressure and the expected higher humidity in the basement due to capillary action.
Since we are building the house with a central ventilation system, connecting the basement rooms to it would be straightforward.
We now have to decide what to do and are a bit unsure. What is your opinion? Does anyone have experience with waterproof concrete and glacial till soil? Is moisture an issue here?
Thank you very much for your input.
We are planning to build a new house with a basement. According to the soil survey, the ground up to a depth of about 5 meters (16 feet) consists of impermeable glacial till. Below that is permeable sand. There is no problem with rising groundwater here. However, due to the soil, surface water can be directed towards the basement wall.
The expert says the basement could be constructed either with masonry and drainage boards on the walls or with waterproof concrete. For masonry, a perimeter drain with a sump pit should be considered. If waterproof concrete is used, the expert states that no drainage is necessary.
The construction company recommends a masonry basement with waterproofing against hydrostatic pressure and perimeter insulation boards. Additionally, a perimeter drain and a sump pit should be installed. Alternatively, they suggest using waterproof concrete with open water management. However, they generally still recommend a perimeter drain with a sump pit for waterproof concrete to avoid long-term problems.
These measures/recommendations would increase the cost of a masonry basement by about €17,000 and for waterproof concrete by €7,000 with open water management or €16,000 with perimeter drainage and sump pit.
Basically, we would lean towards using waterproof concrete, but the recommendation to still install drainage seems a bit like a double safety net to us. The construction company justifies this because of the hydrostatic pressure and the expected higher humidity in the basement due to capillary action.
Since we are building the house with a central ventilation system, connecting the basement rooms to it would be straightforward.
We now have to decide what to do and are a bit unsure. What is your opinion? Does anyone have experience with waterproof concrete and glacial till soil? Is moisture an issue here?
Thank you very much for your input.
Hotdogxxxx schrieb:
Why the additional costs is a good question! According to the cost estimate, the drainage for the partial basement (approx. 50 m² (540 sq ft)) costs around €4,000, and the soakaway pit at about 6 meters (20 feet) deep an additional €8,000. Maybe we got the drainage offered at a particularly cheap price (I don’t think so!), but €4,000 just for drainage when the system can be installed in the open basement excavation seems very expensive to me.
Since the basement is built in glacial clay, drainage without a soakaway pit doesn’t make sense, right? The water can’t drain away. The water from the roof goes into the sewage system.Correct, but in my opinion there are two other options here:
1. You can check whether you can get a permit for discharging drainage water into the sewage system (planning permission / building permit), provided this is technically feasible in terms of elevation.
2. You could consider using a cistern instead of a soakaway pit to store not only the drainage water but also the rainwater from the roof. This probably wouldn’t cost much more (if at all), and you would likely benefit more from it.
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Hotdogxxxx6 May 2021 12:34Thank you very much, Jann!
Yesterday, I spoke again with the surveyor who conducted the soil analysis. The issue with the soil appears to be the very poor water permeability due to the clay layers. Consequently, water would seep from the surface toward the house and press against the foundation walls. With waterproof concrete (WU concrete), this is generally not a problem, but special attention must be paid to sealing around window wells and house entrances, as the water drains very slowly. He also mentioned that with waterproof concrete (WU concrete) without drainage and soakaway pits, internal condensation may occur due to temperature differences, since the external water pressure can cause a refrigerator effect.
In general, measures are also needed to manage water under the standard slab foundation (partial basement), as water can accumulate there during heavy rain.
Regarding costs, a masonry basement with a waterproof membrane (black tank) and drainage/soakaway pit is slightly more expensive than a waterproof concrete version with drainage/soakaway pit.
Therefore, we will probably choose this option.
Yesterday, I spoke again with the surveyor who conducted the soil analysis. The issue with the soil appears to be the very poor water permeability due to the clay layers. Consequently, water would seep from the surface toward the house and press against the foundation walls. With waterproof concrete (WU concrete), this is generally not a problem, but special attention must be paid to sealing around window wells and house entrances, as the water drains very slowly. He also mentioned that with waterproof concrete (WU concrete) without drainage and soakaway pits, internal condensation may occur due to temperature differences, since the external water pressure can cause a refrigerator effect.
In general, measures are also needed to manage water under the standard slab foundation (partial basement), as water can accumulate there during heavy rain.
Regarding costs, a masonry basement with a waterproof membrane (black tank) and drainage/soakaway pit is slightly more expensive than a waterproof concrete version with drainage/soakaway pit.
Therefore, we will probably choose this option.
Hello,
when it comes to the basement, I would never consider anything other than a waterproof concrete structure (WU).... if the black tank system is even slightly poorly executed, you will struggle with damp basements for ages.
Drainage is actually unnecessary for a WU basement (keep in mind there are differences between a WU basement and a "white tank" system), but given the terrain, I might still consider it. First, check your building permit/planning permission to see if drainage is even allowed. Often, you are not permitted to connect an emergency overflow to the sewer system. That can become a problem. In the worst-case scenario, you may have to expect your house to be completely flooded, which definitely rules out a black tank system.
Regarding ventilation: yes, you should definitely connect the basement to the ventilation system. The extra costs are minimal, and this may allow you to design some basement rooms without windows.
Best regards,
Andreas
when it comes to the basement, I would never consider anything other than a waterproof concrete structure (WU).... if the black tank system is even slightly poorly executed, you will struggle with damp basements for ages.
Drainage is actually unnecessary for a WU basement (keep in mind there are differences between a WU basement and a "white tank" system), but given the terrain, I might still consider it. First, check your building permit/planning permission to see if drainage is even allowed. Often, you are not permitted to connect an emergency overflow to the sewer system. That can become a problem. In the worst-case scenario, you may have to expect your house to be completely flooded, which definitely rules out a black tank system.
Regarding ventilation: yes, you should definitely connect the basement to the ventilation system. The extra costs are minimal, and this may allow you to design some basement rooms without windows.
Best regards,
Andreas
H
hanghaus20006 May 2021 12:59I built a waterproof concrete basement (known as a "white tank") and installed drainage pipes under the basement shafts, which then lead into the cistern. This way, the cistern does not need to be installed as deep. The basement has remained dry for 20 years (partly used as a living basement).
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Hotdogxxxx6 May 2021 13:33Thank you all for your opinions.
Since we really have no idea, we are most likely the perfect "cash cow"!!
We are building with a cistern connected to the roof. I just thought that you can’t feed "surface water" into it because sediments would be carried into the cistern, making it dirtier. But now that I think about it, cleaning the cistern is probably the cheaper option compared to the soakaway!
Since we really have no idea, we are most likely the perfect "cash cow"!!
We are building with a cistern connected to the roof. I just thought that you can’t feed "surface water" into it because sediments would be carried into the cistern, making it dirtier. But now that I think about it, cleaning the cistern is probably the cheaper option compared to the soakaway!
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