Costs for renovation and extension of a single-family house from the 70s

Depending on the property and the floor area ratio, in my opinion, an extension would also be an economical option.

What is the (additional) requirement? Depending on the plot and floor area ratio, in my opinion, an extension would also be a cost-effective option.

It is a zone 34, as he says. According to that, an extension would certainly also be possible. Be that as it may: a forum made up of builders cannot give you exact information about costs. However, the demands on technology are not insignificant… that and the roof structure survey costs, costs, costs. Let your architect advise you, that is what he is there for and you are in good hands. I mean, there is nothing here, no floor plan, no section, no photo, on which one could base an assessment. Therefore, everything can only be embedded in well-meaning tips.