Why building a house almost always costs more than calculated

Oh yes, quite a bit will be added over the next few years. The budget currently is around €6,000 just for the KNX components. In total, the electrical work costs around €16,000 and we are doing quite well with that so far.

I find that very little. Is that just the preparation? Regarding KNX, our additional costs are about €30,000-35,000! So we are not doing that. Possibly free@Home, but I am still waiting for a meeting appointment.

But then that's not just a little KNX anymore

Well, there are not only push buttons and actuators, but also wireless window contacts, LED control with Loxone including its MiniServer, motion detectors, etc.

I think that's very little. Is that just the preparation? Regarding KNX, our extra costs are about 30,000-35,000 EUR! So we don't do it either. Maybe free@Home but I'm still waiting for a meeting appointment.

Those are only the material costs, since we do the wiring and programming completely ourselves. Most of your 30,000€ is labor for programming, and most electricians charge a huge markup for the material.

Maybe the electrician just hoped to have found a cash cow to milk

Maybe the electrician just hoped to have found a cash cow there

Right, that would only be a 5% surcharge on the budget, the customer can surely handle that well

What exactly caused the budget to explode for the bathroom, electrical, and kitchen areas aside from the kitchen itself?

Glass fronts and the brand of the kitchen. Built-in fittings for the bathrooms and above-counter washbasins. For electrical, it was the network installation.

I have another one, which I have already described here:

Shortly after moving in, we went there again [Ikea] to buy some missing shelves for the Pax in the dressing room. When we were leaving, my wife then asked me, "Is this still all within our budget?" My answer: "Yes, of course, I had already included that in the special budget for 'black storage boxes because the red ones no longer match color-wise.'" Then my wife: