New construction after triplet birth. Looking forward to your ideas.

Well, you also have to calculate the 2k/m² for the new build, it's basically the same. But with the new build, there are many things you already have. Infrastructure, outdoor facilities, kitchen, garage, etc. It's all already there. Plus the whole stress of a new build, starting from planning, dealing with authorities, getting loan offers, and the construction itself. I won't even start with the move, selling the old property, and so on.

I don't know what prices are like for you, but do you think you would get the difference between an extension and a new build through a sale of your property?

If you are otherwise happy in your house, I would also recommend extending, provided a suitable solution is found for it.
The other option would be way too complicated and time-consuming for me...

An alternative would also be to build onto our current house. For this, an architect has estimated €2000 per sqm and estimates the costs for the living winter garden (40 sqm) at approx. €80k.

Do you already have sketches for this? Possibly attach them as images in post 1, as well as a dimensioned sketch of the existing plot and floor plan of the house.
Why in post 1? Because then it can be found again more quickly.

You can also add a text in post 1, such as:

EDIT: Floor plan images etc. added on xx.xx.xxxx for easy retrieval.
And once you have done that, write a new post here in the thread and point it out.

Then some people here might take half an hour to think along with you.

Interesting perspective from you that you would recommend an extension to us. We've discussed it a lot too, but I fear that you really burn money with an extension!? Or is it (per square meter) not such a big difference whether you extend or build new?

Explain, I dropped out in the middle. Where do you burn money when enlarging the place? You can achieve a lot for 150k, and I would be surprised if that is enough as an extra cost for a new build.

Enlargement means that the additional requirement is added on, the existing building remains.

New construction means: the entire requirement is newly built = a new plot of land is required plus the replacement of the existing building costs the current construction price, the sale of the old building brings the sales proceeds including the increase in value compared to the original construction price, minus fees and taxes associated with the property transfer.

Building an extension on the existing land already saves costs. For the extension, renovation is also needed (an exterior wall now becomes a load-bearing interior wall, windows become passage doors, heating pipes need to be extended etcetera).

Often the cheapest option is an additional storey instead of an extension (i.e. more usable attic space through raising the roof or similar) – you can make sensible speculations here if you know the existing building and its development plan.

Extension or additional storey means a temporary accommodation during the construction period, new construction means money for the old place only comes when you can move out – whereby we are currently elaborating this particular aspect elsewhere:

And if it's actually a new build, then I would build it in such a way that a granny flat can be separated later, which can be rented out. So a two-generation house with one wing just for the children, which is then separated later. You may then possibly be left with a ground floor area or a kind of semi-detached house.

Voluntarily subjecting yourself to a new building? Never. Would definitely choose the extension. Financially also by far the better option.