Plot on a slope; embankment - retaining - costs?

Good day everyone.

We have viewed a plot of land that we like. It is 380m² in size and is located on a (gentle) slope. (Unfortunately, attaching pictures does not work). The plot is intended for the construction of a semi-detached house, the first half already exists. This first half has already fully utilized the allowed ridge height.

"Our" house would stand slightly further forward towards the street than the existing one. We would like to have the ground floor as high as possible. Since the street rises from the neighbor’s to "our" plot by about 60cm and we would build the knee wall lower, we would gain about 1m and thus be about 1m higher than the neighbors.

However, for this we would have to fill up the back of the plot – we also want a level garden. The plot itself is not very steep; I estimate about 10°. However, at the back of the plot it goes down again a bit towards the rear neighbor. Unfortunately, this is not visible in the photos. Here we would have to construct a retaining wall, I estimate about 2m high! Normal L-shaped concrete blocks will probably not be sufficient here, so we need reinforced angle supports on a concrete foundation (right?). At the neighbors on the left and right, L-shaped concrete blocks will also have to be installed. A (partial) basement is of course planned. I hope I have explained everything sufficiently.

Now my questions:

What would be the approximate cost of the earthworks including excavation for the basement, the backfilling at the rear, and the reinforcement all around?

Due to the hillside water, we need a drainage system. But what happens to the hillside water when it hits the angle supports? Does it flow away through the joints? Then you would need some kind of fleece in front so that the soil is not washed away? What else should be considered regarding water on the slope?

What else should we keep in mind? What additional costs could still arise?

Do you have any ideas on how to solve the whole thing cost-effectively? Is there a cheaper alternative to the angle supports (it does not have to look nice since from our side you can’t see this side)?

Many thanks in advance for lots of opinions! If I have forgotten anything, please ask!

Jonibi

Ah, the pictures are there after all

Profile similarity in semi-detached houses? So you have to build the same way as your neighbor? Have you read the regulations about this in the development plan? I would check that first. Often, heights are also specified in development plans, then your consideration is pointless anyway.

The development plan specifies a maximum ridge height of 7.70m, but no profile uniformity. So we are allowed to build further forward and higher. I assume that the 7.70 is measured from the top edge of the street at the lowest point in front of the house. At least that is the case with the neighboring building according to the section. The street slopes up towards us by about 60 cm. Does no one have any idea what the earthworks and the retaining cost?

I think the costs for the earthworks and the [Abfangung] vary greatly by region. We requested quotes from several civil engineers and received quite different offers. The offer we ultimately accepted was also almost honored at the end. It is really best to get several quotes.

No one can tell you in the end what the earthworks will cost.

How do you come up with the 2m? Is that the current height, or does it already include the topsoil removal? If not, in the end you will have to fill between 1.50m and 1.80m on average over 380 sqm. That would be, in the best case, 1000 tons of gravel. (just under 600m³) For the filling material alone, you will pay something between €10,000 and €20,000. Then comes delivery, compaction, and disposal of the remaining topsoil. Your plot is too small to temporarily store the material, so landfill costs for temporary storage may also apply.

Do you have a soil report? If not, there may still be one or the other surprise waiting.

If I had to guess, your earthworks will cost at least €30,000. I wouldn’t estimate less. We paid €22,000 for our earthworks. 300 sqm filled and compacted on average about 1.10m.

Other questions you need to ask yourselves: where is the sewer? At the street up top... that means you probably need a lifting station. And calling it a gentle slope is an understatement, right? Check if building a basement may slowly become financially more sensible.

Do you already have someone who understands construction? An architect? I consider the plot not so easy, and I also see your ideas critically when I look at the neighboring buildings.