ᐅ Significant Water Damage in a New Build – But What Caused It?
Created on: 6 Jan 2024 03:09
S
Simon-L
Good evening!
After living in our new house for almost two years without any significant problems or defects, we unexpectedly discovered water damage in the basement the day before yesterday.
It "started" with a small wet spot near the heating room door. By now, we know that water must be standing on the entire slab, meaning under the screed, and it has already risen slightly into almost all the walls. I will try to describe the situation as concisely as possible, but with enough detail where needed.
First, a few key points:
- A soil test in summer 2020 showed no groundwater or water pressure present
- The slab was made from 25cm (10 inches) waterproof concrete. Since this is a basement used as living space, the entire floor was additionally sealed from the inside
- Because the basement is below the sewer level, we have a sewage lifting system that pumps wastewater from a small bathroom (currently unused) and the basement hallway
- The drain pipes run below the slab and are routed through it. The same applies to the ventilation line for the lifting system
- This consists of a sealed chamber also below the slab, plus a second, top-accessible chamber. Normally, there should be no water in the second chamber as everything flows into and is pumped from the lower chamber. For us, it is basically just an inspection opening
- The small bathroom in the basement is still in its rough construction phase since it is currently not needed. The shower area, roughly 1x1m (3x3 ft), is completely open, so you can see the slab and roofing felt
- Furthermore, the heating room and corridor are not tiled yet, so the screed is visible
Now, a brief summary of events:
- After noticing the spot on the screed and confirming it was not leaking “from above,” I opened the lifting system, which was about half full of water. Water was dripping in from the side. After ruling out a defective pipe (underfloor heating and wastewater from the water softener run nearby), we concluded that water must be coming from inside the screed or insulation layers
- Then we noticed that moisture had risen along ALL walls, both interior and exterior, but only slightly above the screed level
- Bad enough, but the shocking sight was in the non-existent shower area of the bathroom, where water was almost 10cm (4 inches) deep
- We pumped out everything, initially into buckets, removing at least 150–180 liters (40–48 gallons) of water
- More water kept coming in; at first, it was flowing visibly, but thankfully less now. Overall, I estimate about 250 liters (66 gallons) of pumped water so far
- Both the plumbing company and the shell contractor have inspected the site, but so far we have not found the source of the problem. A leak detector is scheduled to come early this week
The following causes can be ruled out:
- Potable water -> The water pipes for the basement apartment are not connected, and the meter does not run if no appliances are on. Other water pipes in the heating room are visible and not leaking or damaged
- Heating water -> Probably not enough to cause this much water on the floor; the underfloor heating system maintains pressure perfectly
- Lifting system -> Works flawlessly. Pumping reliably about half full, and in case of failure, it would sound alarms and log everything precisely. No error entries in recent months
- Defective wastewater pipes -> We first added a large volume of water abruptly, then turned off the lifting system and allowed the pipe system to fill up. This took a long time, but when filled, we monitored the water level through a wastewater pipe, and the level did not drop. So, no leaks
- Sewer backup -> Would have been noticed elsewhere and the water does not smell foul or similar
Sorry, it could not be much shorter...
Gradually, it seems to me that only groundwater pushing up from beneath the slab remains as an explanation, which actually should not happen given the double waterproofing. Since the walls are not wet except at the very bottom near the floor, a defect there seems unlikely.
After reviewing some photos from the construction phase, we noticed that the pipes installed, except for one, apparently lack any seals. One pipe has some kind of black collar, but the other two do not show any sealing.
Do you think it is possible that water is pushing up past the pipes? And can this really cause such large amounts of water and spread across the entire slab? Since all walls are wet, the water must have reached everywhere.
It’s also questionable whether all the water was really STANDING ON the slab or if we pumped out additional groundwater from the soil along with it. At the moment, this is impossible to say.
By the way, the lifting system also has a rubber collar embedded in the concrete. However, a corner was cut out here for the ventilation pipe.
We are aware that it has rained extremely heavily in recent months, probably causing the groundwater level to rise significantly. But as a layperson, I just cannot explain this situation. Is it really possible that 250 liters (66 gallons) of water could fit between the slab and the screed?! Simply incredible.
Thanks in advance for reading and any tips. Best regards!
After living in our new house for almost two years without any significant problems or defects, we unexpectedly discovered water damage in the basement the day before yesterday.
It "started" with a small wet spot near the heating room door. By now, we know that water must be standing on the entire slab, meaning under the screed, and it has already risen slightly into almost all the walls. I will try to describe the situation as concisely as possible, but with enough detail where needed.
First, a few key points:
- A soil test in summer 2020 showed no groundwater or water pressure present
- The slab was made from 25cm (10 inches) waterproof concrete. Since this is a basement used as living space, the entire floor was additionally sealed from the inside
- Because the basement is below the sewer level, we have a sewage lifting system that pumps wastewater from a small bathroom (currently unused) and the basement hallway
- The drain pipes run below the slab and are routed through it. The same applies to the ventilation line for the lifting system
- This consists of a sealed chamber also below the slab, plus a second, top-accessible chamber. Normally, there should be no water in the second chamber as everything flows into and is pumped from the lower chamber. For us, it is basically just an inspection opening
- The small bathroom in the basement is still in its rough construction phase since it is currently not needed. The shower area, roughly 1x1m (3x3 ft), is completely open, so you can see the slab and roofing felt
- Furthermore, the heating room and corridor are not tiled yet, so the screed is visible
Now, a brief summary of events:
- After noticing the spot on the screed and confirming it was not leaking “from above,” I opened the lifting system, which was about half full of water. Water was dripping in from the side. After ruling out a defective pipe (underfloor heating and wastewater from the water softener run nearby), we concluded that water must be coming from inside the screed or insulation layers
- Then we noticed that moisture had risen along ALL walls, both interior and exterior, but only slightly above the screed level
- Bad enough, but the shocking sight was in the non-existent shower area of the bathroom, where water was almost 10cm (4 inches) deep
- We pumped out everything, initially into buckets, removing at least 150–180 liters (40–48 gallons) of water
- More water kept coming in; at first, it was flowing visibly, but thankfully less now. Overall, I estimate about 250 liters (66 gallons) of pumped water so far
- Both the plumbing company and the shell contractor have inspected the site, but so far we have not found the source of the problem. A leak detector is scheduled to come early this week
The following causes can be ruled out:
- Potable water -> The water pipes for the basement apartment are not connected, and the meter does not run if no appliances are on. Other water pipes in the heating room are visible and not leaking or damaged
- Heating water -> Probably not enough to cause this much water on the floor; the underfloor heating system maintains pressure perfectly
- Lifting system -> Works flawlessly. Pumping reliably about half full, and in case of failure, it would sound alarms and log everything precisely. No error entries in recent months
- Defective wastewater pipes -> We first added a large volume of water abruptly, then turned off the lifting system and allowed the pipe system to fill up. This took a long time, but when filled, we monitored the water level through a wastewater pipe, and the level did not drop. So, no leaks
- Sewer backup -> Would have been noticed elsewhere and the water does not smell foul or similar
Sorry, it could not be much shorter...
Gradually, it seems to me that only groundwater pushing up from beneath the slab remains as an explanation, which actually should not happen given the double waterproofing. Since the walls are not wet except at the very bottom near the floor, a defect there seems unlikely.
After reviewing some photos from the construction phase, we noticed that the pipes installed, except for one, apparently lack any seals. One pipe has some kind of black collar, but the other two do not show any sealing.
Do you think it is possible that water is pushing up past the pipes? And can this really cause such large amounts of water and spread across the entire slab? Since all walls are wet, the water must have reached everywhere.
It’s also questionable whether all the water was really STANDING ON the slab or if we pumped out additional groundwater from the soil along with it. At the moment, this is impossible to say.
By the way, the lifting system also has a rubber collar embedded in the concrete. However, a corner was cut out here for the ventilation pipe.
We are aware that it has rained extremely heavily in recent months, probably causing the groundwater level to rise significantly. But as a layperson, I just cannot explain this situation. Is it really possible that 250 liters (66 gallons) of water could fit between the slab and the screed?! Simply incredible.
Thanks in advance for reading and any tips. Best regards!
Thanks for your answers so far!
After soil tests showed that there is no groundwater pressure, it was decided to build a masonry basement. The reason was that, due to the basement apartment (commercial area), there is a lot of flush-mounted electrical installation in the exterior walls, which is somewhat more difficult to do in watertight concrete.
A strip of roofing felt (?) was placed under each wall on the slab. Additionally, after the first course of blocks ("damp-proof course"?), a waterproof slurry was applied as a barrier – this seems to be working well.
The entire basement was then coated twice from the outside with a black sealant and finally waterproofed with roofing felt. The felt was welded up to the bottom edge of the slab. Afterwards, the soil was insulated with EPS boards.
OWLer schrieb:
What do the basement walls look like? Are they also made of watertight concrete?
Are there any photos of the completed (poured) basement from the outside?
After soil tests showed that there is no groundwater pressure, it was decided to build a masonry basement. The reason was that, due to the basement apartment (commercial area), there is a lot of flush-mounted electrical installation in the exterior walls, which is somewhat more difficult to do in watertight concrete.
A strip of roofing felt (?) was placed under each wall on the slab. Additionally, after the first course of blocks ("damp-proof course"?), a waterproof slurry was applied as a barrier – this seems to be working well.
The entire basement was then coated twice from the outside with a black sealant and finally waterproofed with roofing felt. The felt was welded up to the bottom edge of the slab. Afterwards, the soil was insulated with EPS boards.
A
Allthewayup6 Jan 2024 13:55The previous commenters have also brought up another important topic regarding the sealing of the floor slab (Bopa) to the wall. In short, you do not have a joint tape or metal flashing, and therefore no protection against standing or even pressurized water.
Since none of us know the exact circumstances, we can only offer general advice. Given the damage that has already occurred and its extent, I can only recommend that you immediately consult an expert who can compare the construction method with the soil investigation report and analyze potential execution errors or conduct further investigations into the causes.
If there was a soil investigation report that concluded there was no risk of groundwater or standing water, then what went wrong here?
It is quite possible that the builder is relying on the fact that no standing or groundwater was expected, which would make it difficult to hold them liable. In that case, the author of the report would likely come under scrutiny. But all of this is speculation from a distance!
You made the "mistake" of building a basement in today’s conditions. I put “mistake” in quotation marks because as a layperson, it’s easy to be persuaded or to rely on the statements and decisions of professionals. I would never drive a car without a seatbelt or build a basement without a waterproof concrete shell (often called a “white tank” or tanked basement), whether I was building on a peat bog or the top of a hill.
Also, do not rely on your natural disaster insurance, as it does not cover rising groundwater, only surface water (flash floods, heavy rain, etc.).
I’m keeping my fingers crossed for you and please keep us updated here on how the situation develops.
Since none of us know the exact circumstances, we can only offer general advice. Given the damage that has already occurred and its extent, I can only recommend that you immediately consult an expert who can compare the construction method with the soil investigation report and analyze potential execution errors or conduct further investigations into the causes.
If there was a soil investigation report that concluded there was no risk of groundwater or standing water, then what went wrong here?
It is quite possible that the builder is relying on the fact that no standing or groundwater was expected, which would make it difficult to hold them liable. In that case, the author of the report would likely come under scrutiny. But all of this is speculation from a distance!
You made the "mistake" of building a basement in today’s conditions. I put “mistake” in quotation marks because as a layperson, it’s easy to be persuaded or to rely on the statements and decisions of professionals. I would never drive a car without a seatbelt or build a basement without a waterproof concrete shell (often called a “white tank” or tanked basement), whether I was building on a peat bog or the top of a hill.
Also, do not rely on your natural disaster insurance, as it does not cover rising groundwater, only surface water (flash floods, heavy rain, etc.).
I’m keeping my fingers crossed for you and please keep us updated here on how the situation develops.
H
hanghaus20236 Jan 2024 14:27You live in the northwest—doesn’t that area also experience flooding due to heavy rain? Sometimes the groundwater level rises higher than expected there.
Well, that’s unfortunate now. If the bitumen layer was damaged somewhere during backfilling, it could potentially push through not only along the pipes but also through the walls.
A professional expert would definitely be the best option for a solution. It might also be worth talking to the building insurance company to see what can be done.
A professional expert would definitely be the best option for a solution. It might also be worth talking to the building insurance company to see what can be done.
Even if the report states that there is no groundwater, the design water level for impermeable soils should be set at the level of the ground surface (GOK).
Impermeable soils have a hydraulic conductivity (Kf) value of less than 1 x 10⁻⁴ m/s.
So, if there is no clean sand or gravel, the soil is not permeable. Here, it looks like clay... by excavating the basement pit, a basin has been created that will fill up first during heavy rainfall and cause hydrostatic pressure.
Therefore, it is essential to have the soil report checked carefully.
You can also upload parts of it (layer descriptions and soil parameters, building waterproofing).
No additional drainage was installed, right?
Impermeable soils have a hydraulic conductivity (Kf) value of less than 1 x 10⁻⁴ m/s.
So, if there is no clean sand or gravel, the soil is not permeable. Here, it looks like clay... by excavating the basement pit, a basin has been created that will fill up first during heavy rainfall and cause hydrostatic pressure.
Therefore, it is essential to have the soil report checked carefully.
You can also upload parts of it (layer descriptions and soil parameters, building waterproofing).
No additional drainage was installed, right?
schubert797 Jan 2024 09:14And inform the building insurance company in advance/at the same time as a precaution.
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