House purchase single-family house built in 77 how to assess?

Since my parents-in-law have a prefab house of 74 in the same district and I live only a little south of it, I think I know the area well. It is presumptuous of people who claim you are too stupid to look or that 30 km further away is also fine. If, for whatever reasons, you want to stay in the town and nothing is being sold there, then so be it. [Die Neue Heimat] or their bankruptcy and political entanglement were famous and notorious, but they only sold single-family houses from other manufacturers. If the manufacturer cannot be determined, I would definitely commission an expert for pollutant measurement and opening of the interior wall. New electrical installations are not so easy with prefab houses. A new roof is not necessary. Insulation can also be done from the inside. The house is surely still inhabited, and the people survive as well. If you can do a lot yourself and are willing to have a construction site for years, you can and should buy. If the local savings bank already estimated 340,000€ (280+60) in 2018, the increase from 2019-2021 should be added, which was partly 10% per year. I consider the price from the real estate agent to be clearly too low; he just wanted a quick sale since little is currently being bought on the market.

Uh, inheriting is not a change of ownership? Not a tricky question, it could be environmental law related...

then a new burner and a pseudo wood stove in the corner is enough

I was of the opinion that the top floor ceiling must also be insulated if the minimum thermal protection is not met. But I don't know for sure.

It is presumptuous of the people who claim you are too stupid to search or that going 30km further away is also fine.

I have not read that anywhere here either. And at least I even advised against increasing the search radius (others unfortunately advised to do so).

If for whatever reasons you want to stay in the place and nothing is sold there, then that is simply how it is.

Where really nothing is sold, there are reasons (obstacles that can be identified and dealt with).

If the manufacturer cannot be determined, I would definitely hire an expert for pollutant measurement and opening of the interior wall. Rewiring is not so easy with prefabricated houses. A new roof is not necessary. Insulation can also be done from the inside.

The manufacturer is practically irrelevant for this generation of timber frame houses, as can be understandably read in the treatise discovered by the OP. I already recommended thermography and would normally, as long as it is inconspicuous, rather refrain from opening. The possibility of insulating from the inside also applies to exterior walls otherwise. In the specific case, I would replace the insulation (old into the roof, new into the wall) and take the opportunity to retrofit the electrical installation – possibly even by a whole installation level.

then a new burner and a pseudo wood stove in the corner is enough

I do not understand the remark. The question was about the energy retrofit obligation also upon transfer of ownership by inheritance. As far as I know, such an obligation exists after a transfer of ownership, and had asked whether inheritance is treated differently in this regard. As far as I know, basically not, however, the triggering change notification is probably that of the land register (and often a property is transferred to a child earlier than "the old farmer goes to the grave").

If for whatever reason you want to stay in the place and nothing is sold there, then that's just how it is.

Exactly. You just can't complain that you still haven't found anything after 5 years.

since my parents-in-law have a prefab house from '74 in the same district and I live just a little south of it, I think I know the area. [...]

Thanks for the explanations and thanks also to everyone else who is still involved.

With very high probability, the current wall structure looks like this:
8 mm asbestos cement boards
20 mm air
10 mm wood chipboards FP/Y DIN 68761 glued V100
90 mm timber frame
80 mm mineral wool
vapor barrier (transparent plastic foil)
18 mm gypsum plasterboard

The acquaintance who made the offer is currently carrying out a core renovation for a friend on exactly such a Streif house from the year '77.

We are still waiting for the information from a local carpenter about what the renovation of the exterior walls including insulation and the renovation of the roof (insulation + covering + photovoltaics) would cost, because that must be plan B if the plan with the acquaintance falls through.

My wife at least wants to get rid of the asbestos cement boards before we move in—regardless of whether they are harmless as long as they are left undisturbed or not... And leave the rest of the wall as it is. So no new insulation from the inside, only the roof and the windows.
But if the electrical system really has to be redone, then one could insulate from the inside as well.

Tonight we are again thinking of cancelling or negotiating down from €365,000 to €315,000... which is unrealistic and would be equivalent to a cancellation. The new life partner of the sellers—who apparently has a lot to say—already said he is not willing to go down by even a single cent.