Order of renovation single-family house

Well, can you really say that so generally? From 1.4.21 there are still 7.81 cents per kWh of electricity, provided there is something left after own consumption.

With a 10kW system you get approx. €900 feed-in tariff. Costs about €11,000. Thus amortized after almost 12 years. With 30% own consumption you are at 8-9 years. With an electric car maybe after 6 years. I don't think that's a bad investment.

I am not a fan of facade insulation due to the enormous costs. We actually just want to see if we can achieve an efficiency level with new windows and doors and basement ceiling insulation.

Especially with old buildings (your house is borderline here), problems are repeatedly pointed out when installing new windows without improving the exterior insulation, for two reasons:

1.) Greater airtightness allows less air exchange
Modern windows are as airtight as a plastic bag. This requires great discipline when ventilating – which many occupants fail at, causing humidity to rise. Uninsulated walls are cooler than well-insulated walls, which makes dew point undershooting more likely – with the consequences: damp walls, mold growth.

2.) Moisture no longer condenses on the window
The effect from 1.) is disproportionately intensified if the triple-glazed window also insulates better than the uninsulated wall. Then the window would be warmer inside than some spots on the interior wall and almost all moisture would then condense on the latter. The window should always be the coldest point in the room during the heating period, because condensate causes the least damage there – and is also directly visible.

In the 1980s, there was sometimes a bit of thermal insulation (e.g. 6 cm Styrofoam). This could possibly ease your problem somewhat. You still have to keep an eye on it.

We renovated a 70s end-terrace house from the inside last year. Starting with the complete gutting. Then the major trades like removing walls, water pipes, chasing for new electrical wiring, etc. Then everything was redone. The windows were replaced quite early on, when the rebuilding gradually began again. By the way, doors come almost at the end. I find it much more sensible for the floor coverings to already be laid rather than laying them around the door frames afterwards.

We used triple-glazed windows and left the facade as it is. So far no problems, but we also like to ventilate.