Demolition/New construction/Renovation/Building on an old basement - ideas & experiences?

As I already wrote in several places, we bought a plot of land with a small settlement house (semi-detached house) from the 50s on it. The house is about 90 m2 in size and (presumably) partly cellar. The other half of the settlement house, to which we also have to build again, is not cellar. This leads to the fact that if the cellar is demolished, we would probably (?) have to have underpinning done, which sounds costly and not quite straightforward. Therefore, we have now considered whether it might be "easier" to only demolish the house, leave the cellar standing, and rebuild on top of it. Or to renovate the old house and build an extension (but here probably again the problem of different settlement behavior?). We would not only build on the cellar area or where the house now stands, but want to become significantly larger overall (about 200 m2). Therefore, my question now about experiences with building larger on an old cellar? Has anyone here done this? Is that even possible? Is there another option besides having to do the underpinning when demolishing? (Originally I thought you could just fill in the cellar. But apparently that doesn’t work (?)

I would advise against building larger on a basement or floor slab from the 50s - the masonry, foundations, and structural engineering are likely not up to today's standards.

As I have already written in several places, we bought a plot with a small settlement house (semi-detached house) from the 50s on it. The little house is about 90 m2 in size and (presumably) partially basemented.

Have we anywhere - in unfortunately not yet - spoken in plan and picture about the situation? How can a little house be "presumably" partially basemented - are you afraid to go down into the basement?

I would advise against building larger on a basement or slab from the 50s - the masonry, foundations, and statics are probably not up to today's standards.

I do not see it that way. Although I am not formally an engineer, I would not rule it out from the outset. Seeing begins with looking closely, that can clear some fog. Without further examination, I would not want to exclude finding a clever solution for an overbuild that would be statically flexible.

Have we spoken anywhere - in unfortunately not yet - in plan and picture about the situation?
How can a little house be "presumably" partially basemented - are you afraid to go into the basement?

:D
Yes, yes.
But I wouldn’t bet my life on there being no surprises in this property.
At first glance it looks partially basemented.
That means the basement probably does not directly border the neighbor’s house (foundation).

I don’t see it that way. I’m not formally an engineer, but I wouldn’t swear to that from the start. Seeing begins with looking carefully, you can clear some fog that way. I wouldn’t want to rule out without further inspection finding a clever solution for an overbuild that would be statically smooth.

That already sounds somewhat positive.
We will review the building files next week. Until then I only have photos of the exterior of the property, I don’t think that helps much?

From the looks of it, it is partially basemented.
That means the cellar probably does not border directly on the neighboring house (foundation).

That means you were in the cellar, but without a tape measure; and/or you are not sure...

But I wouldn't bet my life on the fact that no surprises will come to light with this property.

... whether an apparent exterior wall is not actually just bricked-up skeletons or hides the secret passage to the nearest Edgar Wallace castle?

We will inspect the building files next week. Until then I only have photos of the property from outside, I think that is not very useful?

The likelihood that you can't make anything out of it at all is rather low.

Do not demolish the entire basement, but only as deep as to not interfere with a new building. Fill the basement and compact it in layers.