Hello everyone,
our soil report arrived last week, and the earth appears to be of good quality and can be used for backfilling.
Unfortunately, a water exposure class W2.2-E was identified, and the developer therefore recommends a waterproof concrete basement structure ("white tank") due to the presence of groundwater pressure. The construction site is a vineyard with a gentle slope, and the winemaker who has worked the land for over 30 years told me in a conversation that he finds this surprising and does not understand where the groundwater pressure would come from.
Of course, we are both laypeople, so my question is: I have heard that soil experts nowadays tend to be cautious and assume a worst-case scenario. Would you install a waterproof concrete basement in this exposure class? What information would you need to be able to give advice on this?
Thank you!
our soil report arrived last week, and the earth appears to be of good quality and can be used for backfilling.
Unfortunately, a water exposure class W2.2-E was identified, and the developer therefore recommends a waterproof concrete basement structure ("white tank") due to the presence of groundwater pressure. The construction site is a vineyard with a gentle slope, and the winemaker who has worked the land for over 30 years told me in a conversation that he finds this surprising and does not understand where the groundwater pressure would come from.
Of course, we are both laypeople, so my question is: I have heard that soil experts nowadays tend to be cautious and assume a worst-case scenario. Would you install a waterproof concrete basement in this exposure class? What information would you need to be able to give advice on this?
Thank you!
I think it unfortunately fits the way the inspector described it in this case.
This concerns temporarily accumulating seepage water that runs down the slope into the backfilled basement pit and can build up against the basement. Limestone is present at the bottom; whether it actually exists everywhere as gravel or was only crushed by the drilling... I wouldn’t take the risk of bypassing the waterproofing with a drainage system there either.
This concerns temporarily accumulating seepage water that runs down the slope into the backfilled basement pit and can build up against the basement. Limestone is present at the bottom; whether it actually exists everywhere as gravel or was only crushed by the drilling... I wouldn’t take the risk of bypassing the waterproofing with a drainage system there either.
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xMisterDx3 Apr 2023 20:24To be honest, is the additional cost of $11,000 really worth it just for the waterproof concrete foundation? Go for it.
What will you do during heavy rain? Vineyards don’t retain any water at all – as was unfortunately seen in the Ahr Valley. In just a few minutes, thousands of liters of water rush down the slope, and your drainage system, which was only possible because the site had Muschelkalk limestone from the late Tertiary instead of early Carboniferous shelly limestone, won’t help you at all at first.
And in a situation like that, everyone here in the forum will probably keep quiet if you start a thread titled “Help, my basement flooded, what nonsense did you all recommend back then?”
What will you do during heavy rain? Vineyards don’t retain any water at all – as was unfortunately seen in the Ahr Valley. In just a few minutes, thousands of liters of water rush down the slope, and your drainage system, which was only possible because the site had Muschelkalk limestone from the late Tertiary instead of early Carboniferous shelly limestone, won’t help you at all at first.
And in a situation like that, everyone here in the forum will probably keep quiet if you start a thread titled “Help, my basement flooded, what nonsense did you all recommend back then?”
A
Allthewayup3 Apr 2023 22:15Judging by the drilling profiles, you really can’t avoid a waterproof concrete shell (“white tank”), Cronos is right about that—especially if it involves more than just a thin layer of sand-lime brick. In that case, your excavation behaves like an artificial basin. Basement light wells can be made water-tight against pressurized water even without concrete; there are proven solutions for that. If your general contractor uses prefabricated elements and you plan to use the basement for living space, external monitoring is required because you then fall under the corresponding usage classification—just as a side note. Also, start familiarizing yourself with the topic of prefabricated walls in waterproof construction. We have the same, and only realized some disadvantages compared to purely cast-in-place concrete after the fact. You should specify in the construction contract which technical standards the basement construction should comply with, for example whether it will be built according to DIN standards or the WU guideline (Waterproof Concrete guideline), etc. In prefabricated construction, the WU guideline is applied in about 99% of cases. It is also important to document that the construction method is compatible with the soil report and does not conflict with it. Afterwards, no one wants to take responsibility for issues ;-)
Discuss the waterproofing strategy for the basement with your general contractor as well. This includes any penetrations through basement walls or the slab. Which waterproofing method will be used for each type of penetration, and so on. Usually, there are several options for execution (masonry collars, annular space seals, etc.). You should aim to minimize penetrations and plan the absolutely necessary ones with maximum security. For example, in our case, we raised the sills of the basement windows, positioned the core drilling for utility connections as high as possible, and executed the seals with a multi-utility entry system (Doyma) pressure-water tight, and so forth.
I would argue that many construction defects in waterproof concrete basements could have been avoided with thorough, forward-looking planning. The basement forms the foundation of the house and should remain dry throughout the building’s lifespan. This does not happen by chance but requires meticulous planning and careful execution. Such a basement is built in just about two weeks and, in my opinion, deserves much more attention than it usually gets. The soil composition generally does not change, but the water saturation may—in some cases substantially—though many tend to overlook this.
In our region, a new dam was built a few years ago, which caused the groundwater level to rise by half a meter (about 20 inches). Since then, thousands of basements have been damp or flooded and some have had to be waterproofed retroactively.
Discuss the waterproofing strategy for the basement with your general contractor as well. This includes any penetrations through basement walls or the slab. Which waterproofing method will be used for each type of penetration, and so on. Usually, there are several options for execution (masonry collars, annular space seals, etc.). You should aim to minimize penetrations and plan the absolutely necessary ones with maximum security. For example, in our case, we raised the sills of the basement windows, positioned the core drilling for utility connections as high as possible, and executed the seals with a multi-utility entry system (Doyma) pressure-water tight, and so forth.
I would argue that many construction defects in waterproof concrete basements could have been avoided with thorough, forward-looking planning. The basement forms the foundation of the house and should remain dry throughout the building’s lifespan. This does not happen by chance but requires meticulous planning and careful execution. Such a basement is built in just about two weeks and, in my opinion, deserves much more attention than it usually gets. The soil composition generally does not change, but the water saturation may—in some cases substantially—though many tend to overlook this.
In our region, a new dam was built a few years ago, which caused the groundwater level to rise by half a meter (about 20 inches). Since then, thousands of basements have been damp or flooded and some have had to be waterproofed retroactively.
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