Buy a house, renovate or build new?

Floors need to be renewed
The facade needs to be painted
Walls need to be wallpapered

PS: This is more or less minor stuff. And you can move in first without painting the facade and do it later sometime.
If you can live with the bathrooms or only do partial renovations there: You save a huge amount of money.

The rest of the equipment (bay window etc.): Top and often very expensive in new buildings.

Is there an information page somewhere or can someone interpret the following u-values for me?

Steel concrete surface wall: 0.435
Masonry surface: 0.396
Walls against soil: 0.503
Wall to unheated basement: 0.660
Roof surface: 0.252
Ceiling to outside air/bay window: 0.305
Ceiling to unheated basement: 0.509
Basement floor against soil: 0.582

And one more thing, who knows a good expert in the [Frankfurt] area?

Google please: U-values new building. The first results have corresponding tables. I have looked at the values, mostly it is naturally better (or must be better, requirements) 20 years later (today). See my post on heating costs above: However, the house is certainly not an energy guzzler, as you can read there. Most existing properties are probably (significantly) worse. Here: What counts are not the U-values (after all, you don’t want KFW funding), but ultimately YOUR heating costs/year; these are manageable at about 1000. The fairly new heating system + solar is a big plus. I don’t know any expert from FFM. Maybe someone else can help here with a tip? Cheers Thorsten

Well, we definitely want to get funding from the KfW through the two programs "Energieeffizientes Sanieren" + "Altersgerecht Umbauen". It would be nice to somehow reach the KFW 100 standard. However, I think that will be difficult to achieve with the house.

Why? The house is certainly not bad.

Just for comparison:
A KFW-70 from 2013/14 has a Q_H of about 50 kWh/sqm/a.

The pellet heating system has a very good Q_p. The TSA adds to that. So the property is not that far from KFW-100 (according to the old regulation, not the current one!) at first approximation.

Of course, an expert must assess the property on site to determine what should be done.

But why the effort? It’s about the costs, I believe the energy renovation is not even remotely worthwhile here. For 40/month or less in savings? If the house had a Q_h of 160, then one could start thinking about it.

Invest money: Only where it makes sense.

In addition, the house has already been partially energy renovated to some (clear) extent 6 years ago through TSA and pellet heating.