Plot for new house construction with basement on a slope - construction costs?

Hello, I wanted to ask, many write here that for a property with a slope, building a basement is recommended. How do you determine that?

Slope = inclined

if you didn’t have a basement, all floors would be above ground, so your foundation slab would be at the level of the upper slope side.
Below that, you would now have a lot of air that you would have to massively fill with gravel and underpin and support with huge foundations.

It is obvious that the lower floor is therefore placed "in the excavation pit," so that part of this floor is underground. This is called a basement.

Basement does not mean that everything has to be concrete. For us, all walls that are underground are made of waterproof concrete, all above-ground walls are built with masonry.

If my answer was not visual enough, imagine this.
Draw a 45° slope (totally exaggerated, yes, but it explains the matter well).
And now draw a house with a foundation slab and no basement on it.
Either your house has to be able to fly or you build a basement underneath.

What do you base that on?

I base it on the rough rule of thumb "200 cm = 100 %," regarding how "urgently" I recommend a basement or advise against omitting one.

If the terrain is sloped, you practically have to put walls under the house (I probably don’t need to add anything to the illustrative explanation by ). As soon as these walls are as high as a basement, you basically have a basement. Although it is filled with earth and cannot be used, and it has no interior walls either, it does not become significantly cheaper because of that.

At one meter height of these factual "basement exterior walls," I estimate (of course roughly) about half the cost compared to having built "with a basement." In other words, from about two meters height, the savings of a "no-basement" are, contrary to the rule of thumb, not quite zero, but so insignificant that it’s not worth it. At least when you factor in a "basement replacement room," the formula should actually hold completely.

At the moment, it seems to be trendy to want to fill the entire hillside plot all around up to the highest point with earth, and to draw these "basement walls" along two or three sides at the property boundaries accordingly. From my point of view, this is pretty much the height of folly.

Hillside plots don’t only have disadvantages, but also have their own charms. Unfortunately, more and more people are currently rushing towards hillside plots who cannot appreciate them and have no idea other than to "flatten" them.

But there are certainly alternatives to my view "the steeper the slope, the more basement": also has a "slope," namely toward "split level." Around 1980, that was very fashionable: dividing floor areas so that the "halves" are offset by half a floor. Or in other words: you attach half of the floor basically to the intermediate landing of the stairs. This works ideally with two equally long stair flights, so with a terrain difference (related to the floor plan) of about 120 to 160 cm.

I can say how we did it.

There were contracts with the neighbors on the left and right with boundary distances that had to be observed. We went to the municipality and clarified with them how we would like to build and what we had planned.

We left the old retaining wall standing. It is also bigger than the new house.
The reasons for this were
- no disposal
- no slope support
- no risk that the slope will slide (42° in the undeveloped part of the property)
- pretty rubble stone wall in the garden
In the area of the house and garage, the new wall is in the ground floor house wall and retaining wall.
We don't have a classic basement, otherwise the garden to the south and west would only be accessible by stairs and a basement is not necessarily needed.

We only had a total of 60 cubic meters of excavation.


I would say it depends on the property whether to have a basement or not. In our case, many hillside properties no longer have a classic basement. Oil tanks, wood, and preserves are hardly used anymore. Most "basements" are real living spaces. The times when basements were dark and damp are over.