Flat rate cost for house renovation - what is realistic?

That means I could theoretically also reverse the estimation, for example by deducting 20% from, say, 3000 EUR new construction?

Basically, the scale should basically be right, but of course it depends a lot on the standard you want to have afterwards, etc. We inspected the existing condition together with the architects to get a rough feel; a flat rate naturally still carries a lot of uncertainty at first. The estimate with the 20% difference was enough for us to say that renovating is really not worthwhile.

Demolition and disposal are not cheap. Old buildings often have larger plots in established locations. Of course, you can buy a building plot – but new housing estates often lack charm. Not to mention the resource consumption at all.

Hello dear forum, If that is the case, why renovate such an old house at all and not just tear it down? Or maybe even forego the purchase altogether and look for a building plot? Because then I pay for land+old house+renovation, instead of just land+new build... Thank you very much and best regards

Demolition and disposal are not cheap. Older buildings often have larger plots in established locations.
Of course, one can buy a building plot - but new development areas often have little charm.
Not to mention the resource consumption.

For context: The demolition and disposal (120 sqm + basement) costs us a total of about 40,000 euros.

And you are right: The issue of resource consumption is indeed still an important argument; a somewhat more efficient new building will never make up for that.

i.e. theoretically, I could also reverse the estimation, for example deducting 20% from a 3000 EUR new build?

... and then you add the 20% back on, because the new plot has to be developed, building applications along with planning have to be created, outdoor facilities with garden/terrace etc. have to be built, and so on.

As a rule, renovation is quite a bit cheaper. But it’s true, you have to be able to live with the existing structure.

Our construction site mantra is: the house already tells us what it wants.

Usually, renovation is quite a bit cheaper. But it's true, you have to be able to live with the existing structure.