ᐅ Basement originally partially constructed with concrete, now possibly fully built with masonry.
Created on: 19 Jan 2017 00:04
K
Kaspatoo
Hi,
In previous discussions and offers, we agreed with our provider (architect/owner of the construction company, including their own site, excavator, employees, etc.) to build the basement roughly half in 24cm (10 inches) thick concrete and the other half with masonry.
The background is that we have a sloped site, and the basement is about half above ground level, containing two living rooms. The rooms at the rear, towards the slope, are a heating room, storage room, and bathroom.
We do not have a soil report. The soil is clay/loam-like (my father-in-law called it red marl). So, it is not very permeable. Above us runs the road, and beyond that, the slope continues for about 50-100m (55-110 yards), then you reach the top of the hill. Two more plots will be developed above us. The house and road are roughly at the same level (plus a step).
We now want to finalize the contract details. The architect recently called me and said he would prefer to build the entire basement with masonry (thickness unknown but thicker than 24cm (10 inches)), including drainage. The drainage would not clog because it would be in a gravel bed.
I have researched and, as expected, I am uncertain about which option is better and what questions I should ask the architect or what details should be agreed upon.
Basically, there are two methods: waterproof concrete (often called a white tank) and sealing with bitumen or plastic membranes (often called a black tank).
Regarding the cost of both options, I have read very different statements; for some, one was more expensive, for others, the other was. Or it was previously like that, but now they say the costs are about the same. The waterproof concrete method is said to be much more common nowadays.
I also found, but only from one source (other sites had exactly the same text), that bitumen variants last only about 30 years, while waterproof concrete easily lasts 80 years. Is there any truth to this? Has anyone had to remove their soil because water appeared after 30 years?
Back to the upcoming discussion with the architect. Should he provide a written guarantee of watertightness? Is the concrete method definitely waterproof and generally requires less long-term warranty? What else should I pay attention to (I won’t sign immediately, but a more confident approach wouldn’t hurt)? What might be a rough but reasonable wording for both options in the contract?
Thank you very much.
In previous discussions and offers, we agreed with our provider (architect/owner of the construction company, including their own site, excavator, employees, etc.) to build the basement roughly half in 24cm (10 inches) thick concrete and the other half with masonry.
The background is that we have a sloped site, and the basement is about half above ground level, containing two living rooms. The rooms at the rear, towards the slope, are a heating room, storage room, and bathroom.
We do not have a soil report. The soil is clay/loam-like (my father-in-law called it red marl). So, it is not very permeable. Above us runs the road, and beyond that, the slope continues for about 50-100m (55-110 yards), then you reach the top of the hill. Two more plots will be developed above us. The house and road are roughly at the same level (plus a step).
We now want to finalize the contract details. The architect recently called me and said he would prefer to build the entire basement with masonry (thickness unknown but thicker than 24cm (10 inches)), including drainage. The drainage would not clog because it would be in a gravel bed.
I have researched and, as expected, I am uncertain about which option is better and what questions I should ask the architect or what details should be agreed upon.
Basically, there are two methods: waterproof concrete (often called a white tank) and sealing with bitumen or plastic membranes (often called a black tank).
Regarding the cost of both options, I have read very different statements; for some, one was more expensive, for others, the other was. Or it was previously like that, but now they say the costs are about the same. The waterproof concrete method is said to be much more common nowadays.
I also found, but only from one source (other sites had exactly the same text), that bitumen variants last only about 30 years, while waterproof concrete easily lasts 80 years. Is there any truth to this? Has anyone had to remove their soil because water appeared after 30 years?
Back to the upcoming discussion with the architect. Should he provide a written guarantee of watertightness? Is the concrete method definitely waterproof and generally requires less long-term warranty? What else should I pay attention to (I won’t sign immediately, but a more confident approach wouldn’t hurt)? What might be a rough but reasonable wording for both options in the contract?
Thank you very much.
Since we are not moving into old concrete bunkers but into heated new buildings, I still wonder why you prefer exterior walls that can absorb moisture. I also don’t understand why you would want these walls to be partly underground and deliberately protect them against water.
Yes, there is no groundwater.
Surface water comes only from the 5m (16 feet) strip in front of the house; all runoff from the street and higher areas remains on the street.
Surface water is redirected sideways back from the house by a slight slope (without flowing back onto the street).
If anything, I am concerned about water pressure coming from the hill.
The drainage system, which will also be connected to the rainwater sewer, is meant to address this.
Regarding the climate, I am not very worried since we have a controlled mechanical ventilation system in the basement.
Only the storage room facing the hill is unheated.
Surface water comes only from the 5m (16 feet) strip in front of the house; all runoff from the street and higher areas remains on the street.
Surface water is redirected sideways back from the house by a slight slope (without flowing back onto the street).
If anything, I am concerned about water pressure coming from the hill.
The drainage system, which will also be connected to the rainwater sewer, is meant to address this.
Regarding the climate, I am not very worried since we have a controlled mechanical ventilation system in the basement.
Only the storage room facing the hill is unheated.
I waterproofed a masonry basement all around for a concrete basement!
If that’s too expensive, do it anyway and try to save money elsewhere.
I want to spare you the details, but digging out, cleaning, and resealing a basement (house built in 1994) on a slope with 2.7 m (9 feet) of excavation is not a pleasant task. The property and garden end up looking like after a new build; everything needs to be redone. Since I have seen the damage that even small roots can cause to the bituminous coating, I wouldn’t let any plants near the basement wall. If people knew this, they would clear out all bushes and vegetation everywhere.
Regards
If that’s too expensive, do it anyway and try to save money elsewhere.
I want to spare you the details, but digging out, cleaning, and resealing a basement (house built in 1994) on a slope with 2.7 m (9 feet) of excavation is not a pleasant task. The property and garden end up looking like after a new build; everything needs to be redone. Since I have seen the damage that even small roots can cause to the bituminous coating, I wouldn’t let any plants near the basement wall. If people knew this, they would clear out all bushes and vegetation everywhere.
Regards
Did you have a drainage system?
Backwater is supposed to be prevented here by means of a drainage system, right?
I found this article from the Association of Private Homeowners, which clearly opposes black tanks and supports white tanks.
Association of Private Homeowners advises: White Tank always the first choice
BERLIN. "White tanks are no longer more expensive than black tanks today. Therefore, they should have long been the standard," demands Dipl.-Ing. Klaus-Dieter Hammes, building expert at the Association of Private Homeowners and head of their Aachen office. "But the opposite is true. Many homeowners still receive a conventional basement under their house and struggle for decades with groundwater pressure. Some turnkey contractors are apparently unwilling to adapt to current technology."
Building professionals distinguish between so-called white and black tanks in basement construction. Black tanks are basements with a concrete slab and masonry exterior walls, which are protected against moisture from the outside before backfilling by applying a black bitumen coating or waterproof membrane. The name comes from the tar-colored surface coating, which usually lasts for about 30 years. White tanks are fully enclosed structures, where all parts consist of high-quality, water-resistant concrete. Experts also refer to this material as WU-concrete (waterproof concrete). Its service life is 60 to 80 years.
"White tanks are indispensable where water presses against basement walls or the floor slab from below or the side, which is the case almost everywhere," says civil engineer Hammes from experience. One cause is the rising groundwater level – because less drinking water is being extracted now than a few years ago. In addition, drainage systems that are supposed to lead rainwater away from the house are often no longer allowed to be connected to the sewer system. This undirected water then also presses as backwater seepage against the basement walls.
White tanks are so-called monolithic structures. They combine structural support and waterproofing in one. Because they are cast in one piece, they are relatively simple to construct — at least theoretically. "In reality, very few companies are able to build a white tank properly," criticizes expert Hammes. Planning a white tank requires a careful investigation of the subsoil. This is impossible without a soil survey. It provides the data planners need to calculate the building components and their reinforcement precisely.
According to the Association of Private Homeowners, implementation is also problematic. "The same mistakes are often made when pouring the concrete," the engineer observes. To ensure that the steel reinforcements are positioned correctly within the concrete, they must be fixed in place before concreting with spacers. Only certain small parts made from plastic or cement-bonded spacers are approved for this. "Many turnkey contractors simply use whatever they have lying around onsite. This is not permitted and leads to damage in the structure." Such negligence is only discovered if an independent expert regularly inspects the construction site.
Another issue is the correct concrete composition. To make it waterproof, additives must be incorporated. "This is also often done incorrectly. The additives are underdosed or used improperly," notes Klaus-Dieter Hammes. The result is inferior concrete that cannot withstand water pressure. The necessary curing of the WU-concrete is also often neglected. Construction firms pour the concrete but then fail to compact it properly with internal vibration, even though correct consolidation is essential for waterproofing. The concrete is also often left uncovered during curing. "However, this is necessary because, due to its chemical composition, the concrete develops very high temperatures during the one- to two-day drying phase called hydration. Insufficient care can lead to stresses and cracks." The Association's advisors observe this repeatedly.
"Although there have been technical guidelines for building waterproof basements for years, most turnkey contractors still do not master the technology," criticizes building expert Hammes. "Homeowners should not leave it to chance but hire an independent expert to regularly inspect their construction site to ensure they ultimately get a truly waterproof basement."
Source: Association of Private Homeowners
However, I think two main reasons are usually given:
- a continuously rising groundwater level
- drainage systems are often not allowed to be connected to the sewer system
I would intuitively say that the first point does not apply to me because of the hillside location.
I’m not sure about the second point yet, but I imagine it would not be a problem anyway, since the drainage is supposed to lead the water away from the house laterally, even if not connected to the sewer.
From there, the water can follow its downhill path; after all, there is no house blocking it anymore.
I am not familiar with the Association but would consider it reputable.
The conversation is scheduled for Saturday.
On request, the architect gave me a rough explanation of the issue again.
Since we are using facing bricks (brick slips), a bearing surface for the bricks is required.
Because concrete walls would be relatively thin and could only support the basement ceiling, the facing bricks would need to bear directly on the basement ceiling, which would then create a thermal bridge.
With masonry walls, the wall can be made thicker, and the facing bricks can be supported partially on the masonry and partially on the basement ceiling.
I am not sure if that makes sense.
Backwater is supposed to be prevented here by means of a drainage system, right?
I found this article from the Association of Private Homeowners, which clearly opposes black tanks and supports white tanks.
Association of Private Homeowners advises: White Tank always the first choice
BERLIN. "White tanks are no longer more expensive than black tanks today. Therefore, they should have long been the standard," demands Dipl.-Ing. Klaus-Dieter Hammes, building expert at the Association of Private Homeowners and head of their Aachen office. "But the opposite is true. Many homeowners still receive a conventional basement under their house and struggle for decades with groundwater pressure. Some turnkey contractors are apparently unwilling to adapt to current technology."
Building professionals distinguish between so-called white and black tanks in basement construction. Black tanks are basements with a concrete slab and masonry exterior walls, which are protected against moisture from the outside before backfilling by applying a black bitumen coating or waterproof membrane. The name comes from the tar-colored surface coating, which usually lasts for about 30 years. White tanks are fully enclosed structures, where all parts consist of high-quality, water-resistant concrete. Experts also refer to this material as WU-concrete (waterproof concrete). Its service life is 60 to 80 years.
"White tanks are indispensable where water presses against basement walls or the floor slab from below or the side, which is the case almost everywhere," says civil engineer Hammes from experience. One cause is the rising groundwater level – because less drinking water is being extracted now than a few years ago. In addition, drainage systems that are supposed to lead rainwater away from the house are often no longer allowed to be connected to the sewer system. This undirected water then also presses as backwater seepage against the basement walls.
White tanks are so-called monolithic structures. They combine structural support and waterproofing in one. Because they are cast in one piece, they are relatively simple to construct — at least theoretically. "In reality, very few companies are able to build a white tank properly," criticizes expert Hammes. Planning a white tank requires a careful investigation of the subsoil. This is impossible without a soil survey. It provides the data planners need to calculate the building components and their reinforcement precisely.
According to the Association of Private Homeowners, implementation is also problematic. "The same mistakes are often made when pouring the concrete," the engineer observes. To ensure that the steel reinforcements are positioned correctly within the concrete, they must be fixed in place before concreting with spacers. Only certain small parts made from plastic or cement-bonded spacers are approved for this. "Many turnkey contractors simply use whatever they have lying around onsite. This is not permitted and leads to damage in the structure." Such negligence is only discovered if an independent expert regularly inspects the construction site.
Another issue is the correct concrete composition. To make it waterproof, additives must be incorporated. "This is also often done incorrectly. The additives are underdosed or used improperly," notes Klaus-Dieter Hammes. The result is inferior concrete that cannot withstand water pressure. The necessary curing of the WU-concrete is also often neglected. Construction firms pour the concrete but then fail to compact it properly with internal vibration, even though correct consolidation is essential for waterproofing. The concrete is also often left uncovered during curing. "However, this is necessary because, due to its chemical composition, the concrete develops very high temperatures during the one- to two-day drying phase called hydration. Insufficient care can lead to stresses and cracks." The Association's advisors observe this repeatedly.
"Although there have been technical guidelines for building waterproof basements for years, most turnkey contractors still do not master the technology," criticizes building expert Hammes. "Homeowners should not leave it to chance but hire an independent expert to regularly inspect their construction site to ensure they ultimately get a truly waterproof basement."
Source: Association of Private Homeowners
However, I think two main reasons are usually given:
- a continuously rising groundwater level
- drainage systems are often not allowed to be connected to the sewer system
I would intuitively say that the first point does not apply to me because of the hillside location.
I’m not sure about the second point yet, but I imagine it would not be a problem anyway, since the drainage is supposed to lead the water away from the house laterally, even if not connected to the sewer.
From there, the water can follow its downhill path; after all, there is no house blocking it anymore.
I am not familiar with the Association but would consider it reputable.
The conversation is scheduled for Saturday.
On request, the architect gave me a rough explanation of the issue again.
Since we are using facing bricks (brick slips), a bearing surface for the bricks is required.
Because concrete walls would be relatively thin and could only support the basement ceiling, the facing bricks would need to bear directly on the basement ceiling, which would then create a thermal bridge.
With masonry walls, the wall can be made thicker, and the facing bricks can be supported partially on the masonry and partially on the basement ceiling.
I am not sure if that makes sense.
Hello,
exactly this
is often the crucial point. For example, this is not permitted here. That means white tank waterproofing is not necessarily required by building regulations, but in reality, you don’t have any other option.
First, find out if you are allowed to drain the drainage water into the sewer. If not, in my opinion, the whole consideration is off right away. Because if you then have to install pump chambers, cisterns, and infiltration systems to get rid of the water, it won’t be cheap. And you’ll have something for the rest of your life that you need to monitor and maintain...! I wouldn’t want that.
White tank waterproofing and that’s it; everything else is just a workaround! Our structural builder told me that he builds about 95% of all basements using the white tank method—there must be a good reason for that.
Best regards,
Andreas
exactly this
Kaspatoo schrieb:
- Drainage is often not allowed to be connected to the sewer system
is often the crucial point. For example, this is not permitted here. That means white tank waterproofing is not necessarily required by building regulations, but in reality, you don’t have any other option.
First, find out if you are allowed to drain the drainage water into the sewer. If not, in my opinion, the whole consideration is off right away. Because if you then have to install pump chambers, cisterns, and infiltration systems to get rid of the water, it won’t be cheap. And you’ll have something for the rest of your life that you need to monitor and maintain...! I wouldn’t want that.
White tank waterproofing and that’s it; everything else is just a workaround! Our structural builder told me that he builds about 95% of all basements using the white tank method—there must be a good reason for that.
Best regards,
Andreas
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