Enlarge and fully renovate a single-family house or demolish and rebuild?

But how do you see it with the walls of the ground floor, which are all supposed to be removed?

I do not see any indications in the plans of bricks with higher compressive strength or calcium silicate bricks, and certainly no differences between the individual interior walls. Except in the basement, only 11.5 cm walls are visible. Due to the shallow depth of the house, it is conceivable that it was built without a load-bearing central wall.

I would immediately fear that these support the ceiling elements (hence probably your question about the ceiling panels) or that the walls also have stiffening functions, even if they are not load-bearing.

The ceiling plan would provide clarification about what kind of ceilings we are dealing with here. A 24 cm wall only in the basement and not above can be an indication of different types of ceilings. A few years earlier, it would have been common to have a reinforced concrete ceiling over the basement, a wooden beam ceiling between the ground floor and attic, and between the attic and the roof space a wooden beam ceiling that structurally already belongs to the roof frame – apparently, this is not the case here. Two assumptions are therefore plausible, which the ceiling plan would answer: either these are also massive reinforced concrete ceilings with typically spans covering on average two rooms, in which case they would (usually at the edges) have to rest on load-bearing walls. No such walls are recognizable from the wall thickness on the floor plan, so it would have to have been solved using bricks with higher compressive strength; these walls are obviously not dispensable and are complicated to substitute. Or, for example, hollow core slab ceilings were used, with (probably parallel to the gable here) continuous beams and elements supplemented with topping concrete. Non-load-bearing stiffening walls would not be dispensable, but replaceable. Blind faith alone would neither carry loads nor resist wind forces, so clarification is necessary.

I didn't mean the building file in the sense of grandpa's folder for the house construction, but the box in the city archive with the building permit documents from back then. We can discuss this provisionally without it here, but then it becomes quite speculative, and the structural engineer doesn't work with a crystal ball either ...

There are no building plans for our house either. Let alone the ceiling plans. I even went to the city's building file archive, and there was only the building permit there as well. Unfortunately, something like that doesn't exist for every house. And ours is only 100 years old, so you would think something like that should still be available. We simply opened up a spot in our house and looked at how the ceilings are constructed, which beams we have at what distances. All nicely noted down.

There are no construction plans for our house either. Let alone the ceiling plans. I was even in the city's building records archive, and there was only the building permit left. Unfortunately, something like that does not exist for every house. And ours is only 100 years old, so you would think something like that should still exist.

No, on the one hand it is actually quite normal that there are (and were) no ceiling plans. On the other hand, something would have to be present there purely by chance, since a house from around 1920 has after all already experienced the Second World War. More archives were bombed out there than Napoleon once said before that stuff from the Caesar era could go into the shredder ;-) In the Middle Ages, there was still a lot of chaos and the urban settlement form was still new, the main driver of the evolution of building regulations were devastating fires. The first development plans were aimed at combating frayed street edges by specifying building line guidelines — so development plans were still very simple: there was a building line on the street side, and the ridge height requirement "not higher than the church tower." Even in the imperial era, there were few regulations: for example, in Berlin there was an eaves height regulation measured by the fact that a house facade could hypothetically collapse like a felled tree before the row of houses opposite, and in the courtyards the turning radius of the fire engine was the measure of all things. Demanding static calculations for the building application is rather recent and there are no iron reinforcements at all in wooden beam ceilings.

We simply opened up a spot at our place and looked at how the ceilings are constructed, what beams we have at which spacings. All nicely noted.

Wooden beam ceilings are very friendly for building forensics, but in the present case this only applies to the one between the attic and the loft, while the ceiling that requires clarification here is the one between the ground floor and the attic.

We currently have a very similar project and have just decided on demolition and complete new construction. Since the house currently has a basement, the hole for a new basement is at least already there. The house is a basement bungalow with just under 80 m² on the ground floor on almost four-digit large land in a very good location, but otherwise has no value or special features that would make it definitely worth preserving. The structure is (unfortunately) quite good, which is why the demolition will hurt just a little bit.

The reasons after two architect appointments were ultimately:

- Adding a floor is ruled out because the floor on the ground floor would have to be raised due to underfloor heating, and then all windows and doors would be too low; so much would have to be done to the masonry that the ground floor could just as well be redone entirely
- Demolishing the ground floor down to the basement is ruled out because it would mean too many compromises (pipes, accesses, the floor plan itself); additionally, an extension leans on the ground floor
- Great uncertainties in the calculation in almost every trade because of "we'll have to see what awaits us"

The structural engineering would have allowed it, but in the end it was the combination of too many compromises and uncertainties.

We currently have a very similar project and have just decided on demolition and complete new construction.

I hope not here and consider it very likely to be more than unnecessary.

Since the house currently has a basement, the hole for a new basement is at least already there. [...] Demolishing the ground floor down to the basement is out of the question because it would mean too many compromises (pipes, access, the layout itself)

So you are now doing a deep demolition and are using nothing but the excavation pit, although OKKD would have also been suitable in terms of height?

This is how you get a nice warm insulated basement with sufficient ceiling height :)