Forgetting perimeter insulation

I spoke with the insolvency administrator myself. He was very friendly and immediately pointed out that it is his job to collect money and that he will reissue the last invoice with more emphasis right at the start of the proceedings, and that we should, to be safe, find a court-appointed construction expert who will determine the value. We should then withhold this amount ...

you should discuss that first with your lawyer. why should you prove how much of the section was done? actually, he should prove that the requested amount was properly executed for the work performed. (whoever wants money must also be able to prove its legality) it is very likely that the defects are not as high-priced as expected according to expert valuation, so that you might actually still have to throw some money behind it. many defects can be easily compensated cheaply through alternative methods (theoretically). practically, however, you probably won't find anyone willing to do that. if you already have an expert there, he can certainly tell you approximately how much the removal of the defects will cost. is the amount roughly at the installment value that the insolvency administrator wants to collect?

at least he wants the money right away and doesn't come with it only in a few years.

whoever wants money must also be able to prove its legitimacy

That may be true, but in practice, when building a house, the contractor will invoice at his discretion and ultimately initiate the legal dunning process. Then the invoice recipient must(!) take action and needs conclusive evidence that the claim is not justified.

Payday: The theory is probably correct. But if I wait until something like this gets through, I will be bankrupt myself before then. Therefore, now the inventory and use this amount of the insolvency administrator's claim to counteract. At least this way I can keep going. Otherwise, I lack all evidence to fend off claims.

ultimately initiate the judicial dunning procedure. Then the invoice recipient must(!) take action and they need solid evidence that the claim is not justified.

I had the "pleasure" of conducting such a dunning procedure against a debtor last year and can therefore say that this is not true. The debtor is contacted by the dunning court and can respond. If they reject the claim, this is communicated to the creditor or a procedure is directly initiated if the creditor requested this when applying for the procedure. In this judicial dunning procedure, no one examines the content, so there are no judgments. It is more of a warning shot for the debtor, as they (if desired) receive the dunning notice from the bailiff. If they say "not true" – which is just a checkmark on the form – then that’s that for the time being. If they ignore it or resign themselves to their fate, you get an enforceable title for little money and in relatively short time. Good thing.

(In my case, the debtor did not respond, let all deadlines expire, so in the end I held an enforceable title. I then sent the bailiff to seize assets, but there was nothing to seize or everything was below the seizure threshold. But the debtor is still young, the title is valid for 30 years, interest accumulates. Eventually ...)

Exactly as Alex wrote, that's how it is! In the dunning procedure, no one checks the claim. No one has to prove anything, neither creditor nor debtor. The creditor can very easily apply for a [Mahn­bescheid] (and thereafter a [Vollstreckungs­bescheid]) without providing any proof of the legitimacy of their claim. The debtor can then, in turn, very easily file an objection to the [Mahn­bescheid] or an appeal against the [Vollstreckungs­bescheid] by simply ticking a box on a form, without having to provide any reasoning or proof, and thus the matter is (for the time being) settled. Then the creditor is under pressure; if they want to pursue the case further, they must assert, justify, and prove their claim in a regular civil court proceeding. After that, the debtor must/can present and prove their perspective. After the evidence has been taken, a judgment is usually issued.

@ TE: I would definitely first talk to your lawyer and consider which course of action is tactically wise before commissioning an expert. But in any case, prepare yourself for the fact that it is not unlikely the matter will have to be settled in a civil court proceeding. The insolvency administrator is obliged to collect outstanding invoices for the insolvency debtor in order to satisfy their creditors. If necessary, also through court proceedings. It is not uncommon for the insolvency administrator to sue over disputed and unpaid invoices. I once worked for almost two years at an insolvency administrator before I ended up in the judiciary. And that was our "daily bread".

A brief update from us:

The surveyor was at the construction site, first photographed everything and already described the defects that are present as very serious in terms of the contract content.
In other words: To achieve the condition we ordered, the building would have to be torn down.
However, he also said at the same time that we can of course achieve a similar U-value through other means than the one we "ordered". This somewhat relieves the emotional burden....

In the meantime, I have gathered some offers and if all goes well, it will still be financially somewhat bearable. The shell builders are of course not exactly competing for the order and point out that they do not want to assume any warranty for the defective substructure – which I almost don't care about anymore...

Our termination is still not finalized because unfortunately I misunderstood the lawyer and must first set a deadline for defect rectification to both the insolvency administrator and the construction company. Once this deadline has passed, we can finally terminate. Only then do I probably have full entitlement to damages – even in case claims are directed at us (which the insolvency administrator has already announced), we would have more weight in our argumentation this way.