Hello, I’m new to the forum and we are currently busy planning our first house. For cost-benefit reasons, we decided against a basement and expect the building’s exterior dimensions to be about 11 x 9 meters (36 x 30 feet). We are still in the initial planning and decision phase and have not chosen a company yet, but we have already received some house offers.
Now to the problem:
On the plot where we want to build, there used to be a house with a basement that was demolished. As a result, there is quite a large “crater” with depths of about 1 to 1.5 meters (3 to 5 feet), although the ground is very uneven. The soil mainly consists of sand and some mineral concrete.
The question that comes to mind is: since we want to build with a slab foundation, a lot will need to be done with the hole first—backfilling, compaction, etc. I just can’t imagine what extra costs this might involve, whether it will stay within a reasonable range or quickly become a five-figure amount.
One construction company even said (they know the plot) why build without a basement if much of the soil is already removed.
We are now a bit uncertain.
Hope you can help me out a little.
Greetings from Franconia
Now to the problem:
On the plot where we want to build, there used to be a house with a basement that was demolished. As a result, there is quite a large “crater” with depths of about 1 to 1.5 meters (3 to 5 feet), although the ground is very uneven. The soil mainly consists of sand and some mineral concrete.
The question that comes to mind is: since we want to build with a slab foundation, a lot will need to be done with the hole first—backfilling, compaction, etc. I just can’t imagine what extra costs this might involve, whether it will stay within a reasonable range or quickly become a five-figure amount.
One construction company even said (they know the plot) why build without a basement if much of the soil is already removed.
We are now a bit uncertain.
Hope you can help me out a little.
Greetings from Franconia
Timo12345 schrieb:
when a large part of the ground is already gone.1–1.5m (3–5 feet) is considered a large part? More likely a fraction, at best half. Even for a slab foundation, you usually go at least 80cm (31 inches) deep, so the question is whether adding fill is really such a big issue. Some information is still missing here. It needs to be clarified whether the existing backfill is load-bearing at all or if it must be completely removed and disposed of. Then the step to a (usable) basement might not be that far. However, this needs to be assessed very specifically on a case-by-case basis, considering the soil conditions, etc. – which this forum cannot provide.
T
Timo1234525 Mar 2017 10:46But I am gaining some insights and can better adapt to the situation. However, you are right about the 80 cm (31 inches) excavation depth for the foundation slab; looking at the area, it might actually be accurate. It is only 1.5 m (5 feet) in the middle section. I assume that when the old house was demolished, the basement pit settled a bit.
I was just hoping to get a rough idea of whether I should expect around 5,000 euros or 25,000 euros.
I was just hoping to get a rough idea of whether I should expect around 5,000 euros or 25,000 euros.
It could be either! Do you have a soil survey? Probably not, but without this information—such as whether there is any groundwater pressure—you can only hope, and that’s risky with such a large amount of money involved.
And with a basement, you can always expect to pay around 50,000 euros, no matter what others tell you. Those 9,999 euro basements usually don’t include anything.
And with a basement, you can always expect to pay around 50,000 euros, no matter what others tell you. Those 9,999 euro basements usually don’t include anything.
T
Timo1234525 Mar 2017 11:33No, we don't have a soil report yet; we're not that far along since we don't have a construction company yet.
I also believe that even if we need to add fill, a slab foundation will be far less expensive than a basement.
I also believe that even if we need to add fill, a slab foundation will be far less expensive than a basement.
G
Gartenfreund25 Mar 2017 16:26Hello Timo
So you have already received quite a bit of information about the basement. I would like to step back from further discussions about the basement since I am not very familiar with the subject, and I have already shared my opinion with you.
Regarding the cistern, I can tell you the following.
I have buried a plastic tank with a capacity of 4 m³ (approximately 140 cubic feet). According to the manufacturer. I once filled it using a non-calibrated water meter and found that, according to the meter, significantly less than 4000 liters (approximately 1056 gallons) actually fit inside. Unfortunately, I cannot provide the exact difference now as I no longer have those measurements. However, the discrepancy was considerable. I can’t say whether this means the tank’s capacity is smaller than stated or if the meter didn’t measure accurately. But I wouldn’t be surprised if manufacturers list the outer volume of the tank rather than the internal capacity. This is just a guess, though.
As I mentioned earlier, this tank is buried. There are shallow tanks and deep tanks (I have a deep one). Shallow tanks are more expensive but do not require digging such a deep hole. The downside is that the remaining water might freeze during winter. Therefore, a tank buried deeper would be better.
I converted an existing property accordingly. This means all roofs and the driveway were connected to the tank, and the existing connections to the sewer system were deactivated.
Specifically, I completely installed new pipes and left the old ones in place. The idea was that if the local authorities ever change their minds and want to charge fees for this again, I could easily revert the system, and they would then manage the rainwater themselves.
What I am about to say applies to what I understand to be the relevant regulations for my situation.
When the tank is full, there is the option to divert excess water into the sewer system, but this incurs fees.
Alternatively, the water can be discharged via a soakaway system.
For this, I would have needed approval from the local water authority, and just asking whether or not that would be approved would have already cost about 100 €.
Additional costs would have come from the soakaway unit itself.
This was a bit too expensive for me, and on top of that, I didn’t know where I could have buried the soakaway unit since there are many trees in the garden.
My alternative solution:
Using a simple sewage pump to ensure the water level does not exceed a certain maximum, and pumping the excess water into a wastewater pipe that I laid above ground in the garden. I cut some cross-slots in this pipe, which allows me to adjust, by rotating the pipe, where more or less water should flow out in case of overflow.
Regarding its appearance, you can hide it reasonably well with suitable plants.
For the size of the tank, take a look under terms like “rainwater tank calculation” or similar. You can find out what size you probably need. But be careful — I found that different websites with the same data can give you very different recommendations.
I can only say that my tank was emptied a few times by the pump in spring 2016, and I could have really used that water in summer. This means it’s better to build a tank that is 5 m³ (approximately 176 cubic feet) too large rather than 1 m³ too small, to put it simply.
I cannot give exact material costs, but approximately:
Tank
750 €
Pipes, bends, etc.
100 €
Two pumps at 40 € each
80 €
Water level switch
50 €
Drainage channel
250 € (you could also choose cheaper options)
Miscellaneous
100 €
That adds up to roughly 1300 €.
But all of this was done as self-installation.
How it will ultimately look for you is something you will have to calculate yourself.
Sorry for the long text. I hope I have answered your questions about the cistern as well as possible.
So you have already received quite a bit of information about the basement. I would like to step back from further discussions about the basement since I am not very familiar with the subject, and I have already shared my opinion with you.
Regarding the cistern, I can tell you the following.
I have buried a plastic tank with a capacity of 4 m³ (approximately 140 cubic feet). According to the manufacturer. I once filled it using a non-calibrated water meter and found that, according to the meter, significantly less than 4000 liters (approximately 1056 gallons) actually fit inside. Unfortunately, I cannot provide the exact difference now as I no longer have those measurements. However, the discrepancy was considerable. I can’t say whether this means the tank’s capacity is smaller than stated or if the meter didn’t measure accurately. But I wouldn’t be surprised if manufacturers list the outer volume of the tank rather than the internal capacity. This is just a guess, though.
As I mentioned earlier, this tank is buried. There are shallow tanks and deep tanks (I have a deep one). Shallow tanks are more expensive but do not require digging such a deep hole. The downside is that the remaining water might freeze during winter. Therefore, a tank buried deeper would be better.
I converted an existing property accordingly. This means all roofs and the driveway were connected to the tank, and the existing connections to the sewer system were deactivated.
Specifically, I completely installed new pipes and left the old ones in place. The idea was that if the local authorities ever change their minds and want to charge fees for this again, I could easily revert the system, and they would then manage the rainwater themselves.
What I am about to say applies to what I understand to be the relevant regulations for my situation.
When the tank is full, there is the option to divert excess water into the sewer system, but this incurs fees.
Alternatively, the water can be discharged via a soakaway system.
For this, I would have needed approval from the local water authority, and just asking whether or not that would be approved would have already cost about 100 €.
Additional costs would have come from the soakaway unit itself.
This was a bit too expensive for me, and on top of that, I didn’t know where I could have buried the soakaway unit since there are many trees in the garden.
My alternative solution:
Using a simple sewage pump to ensure the water level does not exceed a certain maximum, and pumping the excess water into a wastewater pipe that I laid above ground in the garden. I cut some cross-slots in this pipe, which allows me to adjust, by rotating the pipe, where more or less water should flow out in case of overflow.
Regarding its appearance, you can hide it reasonably well with suitable plants.
For the size of the tank, take a look under terms like “rainwater tank calculation” or similar. You can find out what size you probably need. But be careful — I found that different websites with the same data can give you very different recommendations.
I can only say that my tank was emptied a few times by the pump in spring 2016, and I could have really used that water in summer. This means it’s better to build a tank that is 5 m³ (approximately 176 cubic feet) too large rather than 1 m³ too small, to put it simply.
I cannot give exact material costs, but approximately:
Tank
750 €
Pipes, bends, etc.
100 €
Two pumps at 40 € each
80 €
Water level switch
50 €
Drainage channel
250 € (you could also choose cheaper options)
Miscellaneous
100 €
That adds up to roughly 1300 €.
But all of this was done as self-installation.
How it will ultimately look for you is something you will have to calculate yourself.
Sorry for the long text. I hope I have answered your questions about the cistern as well as possible.
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