Basement construction - accept installation of external insulation in January?

It is quite possible to successfully install insulation in December/January (for example, this was done with us), but it depends on the temperatures & weather conditions.

What might even lead to bigger problems is your in-situ concrete - the floor slab will surely be cast as in-situ concrete, and I strongly assume that your precast walls as well as ceilings will then also have to be filled with in-situ concrete. This is all possible in winter as well, but it must be accompanied and protected extremely carefully to ensure proper execution.

By the way, the insulation does not have to be installed immediately - it is quite conceivable, for example, to have the floor slab, walls & ceilings done in January, then insulation & backfilling at the end of February / beginning of March. Depending on the wall area, assembly team & cooperation with the civil engineer, this can be completed within 2-3 days.

Explanation: We have to order the excavation work, the prefabricated house company orders a basement builder who installs the basement into the "hole". And of course, you can securely insulate and seal everything in January as well, but every expert will confirm that if the temperature is -2°C and sleet on that day, these are not good conditions to apply well-adhering insulation. And insulating later (within 4 weeks, hoping the weather is better then) might be an option, but it would certainly involve additional costs in the four-digit range again...

And of course, you can also securely insulate and glue everything in January, but any professional will confirm that if the appointment is at -2° and sleet, these are not good conditions to install a well-adhering insulation.

And insulating later (within 4 weeks, hoping for better weather then) might be an option, but it would certainly be associated with four-figure additional costs again...

But that is not your problem at all. That is the problem of the construction company that owes you a professionally installed insulation. And if the weather is bad and, for example, the adhesive is not approved for these conditions, then the contractor has to wait until the conditions are right.

Accompany it with your expert and sit back and relax. Don't make the construction company's problem your problem.

But that is not your problem. That is the problem of the construction company, which owes you a professionally installed insulation. And if the weather is bad and, for example, the adhesive is not approved for it, then the contractor has to wait until conditions are right.

Accompany it with your expert and relax. Don’t make the construction company’s problem your problem.

From experience, I can say that construction companies build in such a way that it (initially) holds; during the 5-year warranty period, they want peace.
With us, the problems at the first house appeared after 7 years; before that, everything was "spun positively" ("built according to the state of the art," "nothing will happen...").
Conclusion: 40,000 euros paid for renovation. But that is another matter; that’s why I’m cautious about a statement like "That is the contractor’s problem" (in an emergency, they go bankrupt after 2 years, and then I have nothing left from the warranty and construction legal protection...).

With a statement like "That’s the problem of the construction company" (In an "emergency" they go bankrupt after 2 years and then I myself have nothing left from the warranty and construction legal protection...)

But that has nothing to do with your initial question. Because work can also be done in January. And defects can (and probably will) always occur, even when installing insulation in the sunny spring. Poor workmanship is not due to the season.

From experience I can say that construction companies build so that it (initially) holds, they want to have peace during the 5-year warranty.
In our case, problems with the first house appeared after 7 years; before that, everything was "sweet-talked" ("built according to the state of the art," "nothing will happen...").

That can and will always happen from time to time. But "sweet-talking" to me means that problems already occurred during the construction phase or at move-in/start. You have to stay on it right away and not let yourself be postponed. But that is actually another topic.

Your basement will not be able to be installed in "one go" anyway. The foundation slab also needs time to become load-bearing, the walls as well, ceiling elements too (especially in winter). At least a few days lie between. Furthermore, the ceiling supports can only be removed after a certain time (for us it was almost 1 month), i.e. they will have to come by again later anyway.