Assessment of Renovation Costs for End-Terrace House from the 80s - Experiences

if the attic is only used for storage or similar, insulate the top floor ceiling (preferably a ventilated cold roof, then simply roll out 2x24mm mineral wool)

Thank you for the post. As already mentioned here, the house does not have an attic. The rooms on the upper floor are very high and are simply clad with wooden boards. I don't know what this means in practice, but I could imagine that increasing the insulation in this case would not be too difficult. I will add the building description here so that anyone who understands more about it than I do can take a look.

Here is the construction description with more information about the roof, etc.

The numbers are based on a consumption certificate. The question is, if no demand certificate is available, how can the buyer find out?

If there is only a consumption certificate, you only have the consumption. Although it is individual, if three years are taken into account, it is significantly more realistic than a demand certificate.
And for the current purchase, always have the last three years verified (gas bills, heat pump meter, oil consumption with tank invoices, etc.).
Personally, I don’t think much of the demand certificate.