WDVS from a specialist company! Additional costs for a few cm more insulation?

If I had an indication of what a fair price would be, I would look for alternatives or address him once about the [unseriöse Angebot].

For me, the question is what a fair surcharge is for using 2 or 4 cm more insulation.

already told you in post #2 what the material causes in additional costs. From my experience, a markup on the material of about 30% is usual. Your provider is charging 400%.

or address him once about the unprofessional offer.

already told you in post #2 what the material causes in additional costs. From my experience, a surcharge on the material of about 30% is usual. Your provider is charging 400%

Well; what does unprofessional really mean; or how high the surcharge actually is, especially with a general contractor/provider who delivers turnkey, is always difficult to predict.

Tendentially, in such businesses, the standard in the construction service description is rather tightly calculated to have a “competitive” offer on the market. The actual profits are then generated with any add-on.

I also understand that the ISO subcontracts; then it is even more likely that he wants to make more than just the ongoing costs.

Also, if he installs 95% or more as quasi standard in such a case, there is organizational additional effort involved; also regarding remnants etc.

And only he can tell you what his purchase costs are.

Either you leave out the additional insulation; or you take the trade out (although the credit from the general contractor will probably be less than expected) and have it done elsewhere.

However, what becomes interesting is a reduced consumption of my heat pump (according to the Energy Saving Ordinance for heat approx. 12,500 kWh/a regarding the design of the photovoltaic system.

Heat demand? Then / 4 = your possibly expected electricity consumption. Seems high to me.
We live in a cold area of the country (yes, there is still snow here), need almost 3,400 kWh of electricity including controlled residential ventilation and hot water...

As my physics teacher would have written: Units! Or to deliberately misunderstand you: 4 euros surcharge for one centimeter thicker insulation on the entire house is dirt cheap...

4 euros is cheap, I recently bought 10cm panels and the price compared to the 8cm thick ones was about 2 euros per m2 higher, okay, hardware store prices but still comparable.

But then you probably need longer dowels, which also increases the transport volume because instead of 10 panels, there are only 8 in the package and so on.

What about the window sills, who installs them?

I find the price okay.