Approximate cost for 50 sqm extension

Yes, sorry, I should have addressed that: the plot ratio is currently maxed out at 0.14. However, I had already called the responsible lady at the building authority and she said the area is now at 0.2, so in principle she sees no problem with that. But of course, you are only 100% sure once you have the building permit.

I also think that unfortunately your lower limit is not sufficient. Eight years ago, for a 40 sqm single-story extension, we ended up at €3400/sqm (high-quality parquet, floor-to-ceiling glass all around, “only” designer radiators, elaborate raised ground floor veranda) including all work phases completely through an architect and with local craftsmen. Unfortunately, the general rule is that an extension is usually not cheaper than a new build. The cost advantage due to the existing structure is eaten up by the relatively small volume and the fiddly work, at least if you don’t do much yourself. What I notice: you write 50 sqm extension plus roof terrace, don’t you have to calculate costs for the terrace as well? A roof terrace is also elaborate. My advice: before buying, get a cost estimate from an architect who knows about such things (= knows suitable craftsmen and current prices). And have you already used the search function here in the forum on the topic “Anbau”? Good luck!

We had planned a similar extension almost two years ago by now and came to almost €3000/sqm, and then stopped the project. We had planned with a timber frame construction. And normal standard.

Yes, sorry, I should have addressed that: the floor area ratio is currently maxed out at 0.14. However, I had already called the responsible lady at the building authority and she said that the area is now at 0.2, so she basically sees no problem with that. But of course you are only 100% sure once you have the building permit.

Problem: you can mention a lot over the phone. Either it is a 0.12 area or it is a 0.2 area. Building plans also get changed over time, but then that's how it is and not "the area is". On the other side of the street it might be 0.2, with you only 0.12. That's just how it is. I would file a building inquiry: drawing into the site plan and that's it. Then you have certainty.

You write 50 sqm extension plus roof terrace,

He wants 35 sqm downstairs and 15 sqm upstairs, the rest will be roof terrace. But you are kind of right.

My experience with building authorities is also that, on the phone or even during a non-binding appointment, everything is basically possible for reasons of conflict avoidance. If the use depends on an expansion for you, I would not buy the house without a written commitment from the responsible specialist department. If you have the time for a preliminary building enquiry.