Construction supervision via Bauherren-Schutzbund, Association of Private Builders, TÜV, DEKRA, independent expert surveyor, or "xyz"...?

2. Invoices are not submitted to KfW Bank, but are settled with the approved and prepaid repayment grant

This was about the funding of the construction supervisors. So Program 431. You submit the invoice and application to KfW after completion of the measure and receive the grant paid out. However, with the repayment subsidy in KFW 153, you are right, it is offset against the remaining debt after the measure is completed.

We consciously decided against an expert, as we feared that this would negatively affect the relationship between us and the construction company.

We are not quite at the end yet, but so far I would draw a mixed conclusion. As with every construction project, some unforeseen things have also happened with us. In almost all cases we discovered * - not necessarily always defects in the sense of construction defects, but also planning inaccuracies - the construction company has accommodated us. Sometimes not immediately and only after urging, but then sometimes even on a Sunday, for which we still want to give our site manager something proper as a gift . Of course, I still had some sleepless nights (especially at the beginning).

I believe it wouldn't have been different with an expert. I think in some cases one could have insisted more vehemently on one's rights and certainly could have negotiated price reductions – but the downside would surely have been that the general contractor would have scrutinized the contract very closely and "shown his appreciation" elsewhere – at least that's my assumption.

I am curious to read about other builders’ experiences with experts.

If I could start again, I might build with an independent architect who takes over all phases including detailed planning. To not exceed the budget – I am firmly convinced that good planning costs accordingly more – I would probably then build about 25 m² smaller.

* we looked very closely and read a lot, but certainly overlooked some things due to lack of technical knowledge and also "unlawfully" demanded other things – I think this is exactly where a key point of the discussion will lie.

First of all: The survey will be very unrepresentative, since the people who click on the thread are more likely those who have commissioned one; many who think it is also possible without one are not interested in the thread at all.

I think a construction expert is useful because as a layperson you can easily be talked into the ground, whereas the construction expert can talk to the construction company on equal footing.

We have one from the Bauherren-Schutzbund, he costs €312 per site visit (a total of 9 visits).

I would involve him from the very beginning. He usually knows all regionally relevant construction companies and knows which companies have had construction defects before or not, and can advise one accordingly when selecting. He can also check the contract documents and already pay attention to a correct customer-friendly contract design.