Backfilling for foundation slab

So I also believe that with a slab foundation, even if we have to backfill, it is far below the price of a basement.

That totals about 1300 €. But everything is DIY.

Filling in cannot be that wild.

For 1300€ I can water my garden here for 30 years. The prerequisite is a water meter for the outdoor water connection, so that only fresh water is paid for and no wastewater.

Filling sand costs 13 per ton. Concrete recycling 20 per ton. One hour of excavator 80,- All plus tax. The filling can’t be that wild. Karsten

Hello Timo

So you have already received some information about the cellar. Regarding further discussions about the cellar, I would like to hold back a bit now 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 buried a plastic tank with 4 m³ capacity according to the manufacturer. I once filled it using a non-calibrated water meter and noticed that according to the water meter significantly less than 4000 liters fit inside. Unfortunately, I cannot specify the exact difference now as I no longer remember the exact values. However, it was a considerable difference. Whether this means the tank’s capacity is smaller than stated or the meter did not measure correctly, I cannot say. But I would not be surprised if manufacturers state the exterior volume rather than the interior volume as the tank size. But as I said, just a guess.

As mentioned above, this tank will be buried. There are flat tanks and deep tanks (I have one like that). Flat tanks are more expensive, but you don’t need to dig such a deep hole. The disadvantage is that you have to expect that water still present in winter can freeze. Therefore, a tank buried deeper is better.

I have converted an existing property accordingly. This means all roofs as well as the driveway were connected to the tank, and in return, the existing connections to the sewer were decommissioned.
Specifically, I laid the pipes completely new and left the old ones in place, under the motto: in case the city changes its mind and wants money again, I can relatively easily convert back and they can then take care of the rainwater.

What I am saying now refers to what applies here to me according to my knowledge.

When the tank is full, there is, on one hand, the option to direct the surplus into the sewer. But this costs fees again.

It is possible to dispose of it via infiltration trenches.
For this, I would have needed a permit from the Lower Water Authority where just the question of whether or not it would be approved would have already cost €100.
In addition, there would have been costs for the infiltration unit.

That was a bit expensive for me, and besides, I wouldn’t have known where to bury such an infiltration unit since many trees are in the garden here.

My alternative:
Using a simple wastewater pump to ensure that the water level reaches only a maximum value and that the excess water is then pumped into a sewage pipe which I laid above ground in the garden. I cut some cross-slits into this pipe so that by rotating it accordingly, I can more or less set where, in a case of emergency, more or less water should run out.
Regarding the appearance, this can be more or less well concealed by appropriate planting.

As for the tank size, have a look under “Rainwater tank calculation” or similar terms to find out what size you might need. But beware, I found that with the same data, different websites may give different results.
I can only say that my tank was partially emptied several times by the pump in spring 2016, and I could have used that water well in summer. This means better to build 5 m³ more than 1 m³ too little tank capacity. To put it that way.

I cannot give the exact material costs. But roughly:

Tank €750
Pipes, elbows, etc. €100
two pumps at €40 each €80
Water level switch €50
Drainage channel €250 (cheaper options were also available)
Miscellaneous €100

Totaling approximately €1300.
But all as DIY.

How it looks for you in the end you have to calculate yourself.

Sorry this text got a bit long. But I hope I have answered the questions about the cistern as well as possible.