Is the architect's cost estimate realistic?

I would have calculated/verified: Complete renovation 105sqm at €2,500/sqm New build 50sqm at €3,000/sqm plus additional construction costs So €412,500 + €62k additional costs (simply assumed by the architect) ==> €464,500 + 10% buffer €40,000 ==> total €514,500 For me, the kitchen is separate since it has nothing to do with the renovation. So approx. €530k off the top of my head. The architect is not doing badly at all and at least quite cautious. And the expectations from the other thread are confirmed. Even if it hurts.

But you are still missing the €150k for the plot.

I am chiming in here because we are pursuing a similar project (semi-detached house from 1930, 1.5 stories, with 100sqm full renovation, followed by a 90sqm extension, two stories, timber frame construction). We have also calculated €2500/sqm for the renovation of the existing building (everything except the foundation walls removed and rebuilt, including a new pitched roof) and €3000/sqm for the extension, because we find that figure to be a realistic range everywhere. Is that realistic? Or aren’t there overlaps? For example, the heating system is only installed once. Is it not roughly included both in the €2500 and the €3000? The same goes for photovoltaic systems, for example.

Is that realistic? Or aren't there overlaps? For example, the heating is only installed once. Isn't it roughly included both in the €2500 and the €3000? The same applies to photovoltaics, for example.

If you only want to heat the existing building or only the extension, then of course it will be cheaper... You have to install the underfloor heating everywhere. There are overlaps, but not to the extent that the numbers would fundamentally change...

Of course, I am aware that, for example, radiators etc. have to be installed in all rooms. But what about the heat pump that is installed outside? Or the costs for the front door? Costs for the bathroom? That should amount to a few thousand, right?

Of course, I’m aware that, for example, radiators etc. need to be installed in every room. But what about the heat pump, which is installed outside? Or the costs for the front door? Costs for the bathroom? That should amount to a few thousand euros, right?

3000€/sqm is a guideline for a standard house, simple and practical, plastered. Standard bathroom, no high-end luxury bathroom. Plastic front door, no wood, no aluminum.
It’s cheaper to build in the north, more expensive in the south. If you want to use higher-quality materials or improve the KfW standard with photovoltaics, these costs are added on top.